PELAGIC NEARFSHORE ABUNDANCE OF INVERTEBRATES IN LAKE MICHIGAN COMPARED TO ENTRAINMENT AT THE LUDINGTON PUMPED STORAGE POWER PLANT By Rick Ligman A THESIS Submitted to Michigan State University in partial fulfillment of the requirements ' for the degree of MASTER OF SCIENCE > Department of Fisheries and Wildlife 1981 Au» va- 5‘ a ABSTRACT PELAGIC NEAR-SHORE ABUNDANCE OF INVERTEBRATES IN LAKE MICHIGAN COMPARED TO ENTRAINMENT AT THE LUDINGTON PUMPED STORAGE POWER PLANT By Rick Ligman Estimates of day/night distribution, abundance, and survivorship of macroinvertebrate drift organisms cycled through a pumped storage power plant were made in 1979. Bi-weekly sampling with 3511; meter nets yielded estimates of organism abundance in adjacent Lake Michigan and at the plant site. Lake collections were dominated by Mysis relicta, four chironomid subfamilies, three species of'amphipods and naidid oligochaetes. These groups were also collected at the plant though order of abundance was not identical. Densities were highest in night collections. Mysis densities peaked lakeward of the 6m contour. Highest total chironomid densities occurred shoreward of the 6m contour. Amphipod density increases were associated mainly with release of Juveniles in mid-summer. Roughly 3% of entrained mysid were returned to Lake Michigan with values of 10h, 55, and 20% recorded for chironomids, Gammarus sp. and Pantoporeia Sp. Loss estimates were principally affected.by low release rates. ACKNOWLEDGEMENTS I wish to acknowledge Michigan State University, Department of Fisheries and Wildlife for providing the equipment and facilities that enabled me to complete this study. I am very grateful to both the Consumers Power and Detroit Edison Companies for providing funds and access to the study site. I sincerely thank Dr. Charles R. Liston for serving as my major professor and for providing this research opportunity. I also thank my committee members Dr. Niles R. Kevern and Dr. Richard R. Merritt. I am grateful to Dr. Edward J. Grafius for substituting for Dr. Merritt at my oral examination. The encouragement and humor of Dan Brazo, Field Director of the Ludington Research Laboratory, enabled me to continue during stressful times and I am grateful. Mr. Joseph Bohr's wizardry with Fortran and knowledge of statistics helped me complete what seemed an insurmountable task, and I am grateful. Fellow graduate students and cadworkers Fred Koehler, Rich O'Neal and Greg Peterson are thanked for the many long hours and sleepless nights spent helping me collect this information. The following undergraduate students aided in the 1979 - 1980 data collections, often under adverse conditions: Steve Andrews, Donna Brewczak, Sara Chubb, Tom Graf, Steve Lambert, Mike Stroyan, Mary Whalen, Bob Williamson, Steve Wilson and Rich Yanusz. ii Mr. Leo Yeck, boat captain of the R/V’fbbert L. provided much in the way of overall knowledge, safety consciousness and worldly philosophy for which I am grateful. A special thanks is offered to Ms. Barbara Poppema for her typing ability, humor and perfectionist attitude. Finally, a special thank you to my parents, Harold and Berneice Ligman and the other members of my family. I hope that they realize my appreciation for the support they provided, though it is not often displayed. iii LIST OF TABLES . . . . LIST OF FIGURES . . . INTRODUCTION . . . . . DESCRIPTION OF SITE . mmons O O I O . O O 0 TABLE OF Farfield . . . . . . . . . Entrainment - Extrainment Reservoir . . . Mbrtality . . . RESUIlTS O O O O O O O Farfield . . Entrainment . . Reservoir . . . Extrainment . . Mysis relicta . Farfield . Entrainment Reservoir . Extrainment Losses to Lake Michigan Chironomidae . . . . Farfield . . . Entrainment Reservoir . Extrainment ' Gammarus spp. . Farfield . Entrainment Reservoir . Extrainment CONTENTS . . . . . . . . . . . . . . 1 . . . . . . . . . . . . . . 4 . . . . . . . . . . . . . . 8 . . . . . . . . . . . . . . 14 . . . . . . . . . . . . . . 16 . . . . . . . . . . . . . . 16 . . . . . . . . . . . . . . 18 . . . . . . . . . . . . . 18 . . . . . . . . . . . . . . 20 . . . . . . . . . . . . . . 22 . . . . . . . . . . . . . . 24 . . . . . . . . . . . . . . 26 . . . . . . . . . . . . . . 26 . . . . . . . . . . . . . . 30 . . . . . . . . . . . . . . 32 . . . . . . . . . . . . . . 32 . . . . . . . . . . . 35 . . . . . . . . . . . . . . 35 . . . . . . . . . . . . . . 35 . . . . . . . . . . . . . . 43 . . . . . . . . . . . . . . 45 . . . . . . . . . . . . . . 48 . . . . . . . . . . . . . . 48 . . . . . . . . . . . . . . 48 . . . . . . . . . . . . . 58 . . . . . . . . . . . . . . 58 . . . . . . . . . . . . . . 63 iv Pontoporeia hoyi Farfield . Entrainment Reservoir . Extrainment Oligochaetes . . Farfield . Entrainment Reservoir . Extrainment Minor Taxa . . . Farfield . Entrainment DISCUSSION . . . . . . Mysis‘relicta Chironomidae . . Amphipoda . . . Oligochaeta . . Minor Taxa . . . SUMMARY LITERATURE CITED . . . 84 84 98 104 109 112 115 120 LIST OF TABLES Table 1 Sampling dates, locations, and number of macroinverte- brate samples taken in 1979 at the Ludington Pumped Storage Project. 2 Estimated numbers of macroinvertebrates entrained in the Ludington Pumped Storage Reservoir on sample dates during 1979. 3 Number of macroinvertebrates entrained in the Ludington Pumped Storage Reservoir during the 0200 (1) and 0500 (2) sample periods in 1979. 4 Total number of macroinvertebrates estimated to be entrained and released at the Ludington Pumped Storage Reservoir during sampling in 1979. 5 Numbers of Mysis relicta estimated to be contained within contour intervals in a 2.4 x 9.7km hypothetical rectangle near the Ludington Pumped Storage Power Plant in 1979. 6 Total number of Mysis relicta estimated to be entrained into the Ludington Pumped Storage Reservoir. 7 Mean densities of Mysis relicta (#/1000m3) in samples from the Ludington Pumped Storage Reservoir during 1979. 8 Total number of Mysis relicta estimated to be released from the Ludington Pumped Storage Reservoir during 1979. 9 Numbers of Chironomidae estimated to be contained within contour intervals in a 2.4 x 9.7km hypothetical rectangle near the Ludington Pumped Storage Power Plant in 1979. vi Table 10 11 12 13 14 15 16 17 18 19 20 21 Numbers of Chironomidae pupae estimated to be contained within contour intervals in a 2.4 x 9.7km hypothetical rectangle near the Ludington Pumped Storage Power Plant in 1979. Total number of Chironomidae estimated to be entrained into the Ludington Pumped Storage Reservoir. Mean densities of Chironomidae (#/1000m3) in samples from the Ludington Pumped Storage Reservoir during 1979. Mean densities of chironomid pupae (#/1000m3) in samples from the Ludington Pumped Storage Reservoir during 1979. Total number of Chironomidae estimated to be released from the Ludington Pumped Storage Reservoir during 1979. Total number of chironomid pupae estimated to be released from the Ludington Pumped Storage Reservoir during 1979. Numbers of Gammarus pseudolimnaeus estimated to be contained within contour intervals in a 2.4 x 9.7km hypothetical rectangle near the Ludington Pumped Storage Power Plant in 1979. Numbers of Gammarus fasciatus estimated to be contained within contour intervals in a 2.4 x 9.7km hypothetical rectangle near the Ludington Pumped Storage Power Plant in 1979. Total number of Gammarus pseudolimnaeus estimated to be entrained into the Ludington Pumped Storage Reservoir during 1979. Total number of Gammarus fasciatus estimated to be entrained into the Ludington Pumped Storage Reservoir during 1979. Mean densities of Gammarus pseudolimnaeus (#/1000m3) in samples from the Ludington Pumped Storage Reservoir during 1979. Mean densities of Gammarus fasciatus (#/1000m3) in samples from the Ludington Pumped Storage Reservoir during 1979. vii 42 44 46 47 49 50 55 57 59 60 61 62 Table 22 23 24 25 26 27 28 29 30 31 32 Total number of Gammarus pseudolimnaeus estimated to be released from the Ludington Pumped Storage Reservoir during 1979. Total number of Gammarus fasciatus estimated to be released from the Ludington Pumped Storage Reservoir during 1979. Numbers of Pontoporeia hoyi estimated to be contained within contour intervals in a 2.4 x 9.7km hypothetical rectangle near the Ludington Pumped Storage Power Plant in 1979. Total number of Pont0poreia hoyi estimated to be entrained into the Ludington Pumped Storage Reservoir during 1979. Mean densities of Pontoporeia hoyi (#/1000m3) in samples from the Ludington Pumped Storage Reservoir during 1979. Total number of Pontoporeia hoyi estimated to be released from the Ludington Pumped Storage Reservoir during 1979. Numbers of naidid Oligochaetes estimated to be contained within contour intervals in a 2.4 x 9.7km hypothetical rectangle near the Ludington Pumped Storage Power Plant in 1979. Mean densities of naidid Oligochaetes (#l1000m3) in samples from the Ludington Pumped Storage Reservoir during 1979. Total number of naidid Oligochaetes estimated to be released from the Ludington Pumped Storage Reservoir during 1979. Numbers of Heptageniidae estimated to be contained within contour intervals in a 2.4 x 9.7km hypothetical rectangle near the Ludington Pumped Storage Power Plant in 1979. Numbers of Siphlonuridae estimated to be contained within contour intervals in a 2.4 x 9.7km hypothetical rectangle near the Ludington Pumped Storage Power Plant in 1979. viii 64 65 68 70 72 73 76 79 8O 81 83 Table 33 34 35 36 Survivorship of Mysis cycled through the Ludington Pumped Storage Reservoir in 1979. Survivorship of Mysis cycled through the Ludington Pumped Storage Reservoir in 1980. Survivorship of amphipods cycled through the Ludington Pumped Storage Reservoir in 1979. Survivorship of amphipods cycled through the Ludington Pumped Storage Reservoir in 1980. ix Page 95 96 110 111 ll Figure LIST OF FIGURES Macroinvertebrate sampling stations, Ludington Pumped Storage Project. Schematic drawing of the aluminum sled with attached plankton net used for sampling at the 1.5m contour. Density (No./1000m3) of Mysis relicta at different stations and contours near the Ludington Pumped Storage Power Plant in 1979. Density (No./1000m3) of chironomids at different stations and contours near the Ludington Pumped Storage Power Plant in 1979. Density (No./1000m3) of chironomid pupae at different stations and contours near the Ludington Pumped Storage Power Plant in 1979. Density (No./1000m3) of Gammarus pseudolimnaeus at different stations and contours near the Ludington Pumped Storage Power Plant in 1979. Density (No./1000m3) of Gammarus fasciatus at different stations and contours near the Ludington Pumped Storage Power Plant in 1979. Density (No./1000m3) of Pontoporeia hoyi at different stations and contours near the Ludington Pumped Storage Power Plant in 1979. Density (No./1000m3) of Oligochaetes (Naididae) at different stations and contours near the Ludington Pumped Storage Power Plant in 1979. 12 27 36 40 51 53 66 74 INTRODUCTION The littoral area of Lake Michigan has been documented to be used as both a spawning site and nursery area by most fish species (Liston et a1. 1980, Brazo and Liston 1979, Jude 1977) and as an area of high invertebrate production (Mozely and Garcia 1972, Robertson and Alley 1966). The literature describing macroinvertebrate fauna deals almost exclusively with depths greater than 10m. Quantitative treatment of macroinvertebrates inshore of the 10m contour is nearly nonexistent. The littoral zone of lakes occupies the interface between the terrestrial and aquatic ecosystems. Allochthonous organic inputs coupled with auto- chthonous production produce a diverse and dynamic community of organisms. The role of the littoral biota is significant in this respect, since organisms remove and concentrate nutrient inputs from both the terrestrial and aquatic environments as biomass. Anthropogenic activities may have a significant impact on this portion of the aquatic ecosystem via point and non-point source perturbations. Operational effects of hydroelectric power generating facilities singly, or in combination, may have a significant adverse effect on organisms using the littoral zone for either a portion or all of their developmental sequence. Macroinverte- brates provide a large portion of the forage base for fish species in eastern Lake Michigan such as yellow perch, lake whitefish, round white- fish, burbot, ninespine stickleback, trout-perch, sculpins, adult bloaters and immature salmonids (Yanusz 1979; Ligman 1978; Mikus 1978; Armstrong et a1. 1977; Bauer 1975; Brazo 1973). Impact assessment of operational effects of electric power gener- ating facilities on macroinvertebrate populations has recently received increased attention. Environmental studies conducted at both nuclear and fossil fuel generating stations have indicated mortalities of less than 1002 for organisms entrained in condenser cooling water (Cannon et a1. 1977; Ginn et a1. 1977; Carter 1977; Nalco 1976). Pilot studies conducted at the Ludington Pumped Storage Power Plant in 1978 indicated that mortalities incurred by macroinvertebrates entrained in the source water were below 1002 (Liston et a1. 1980). High survivorship was expected since water cycled through the power plant is not used for cooling purposes, nor are biocides added to the flowing water. However, turbine passage does subject organisms to increased turbulence, rapid hydrostatic pressure changes, and mechanical abrasion through contact with internal metal surfaces. Macroinvertebrate mortality evidenced is a response to the singular or combined effects of these stresses. These potential stresses coupled with the huge volumes of water (maximum of 341m3/s pumping; maximum of 358m3/s generating, per unit) cycled between the upper reservoir and Lake Michigan further underline the importance of determining survivorship for organisms passed through the turbines. This investigation was directed towards assessment Of the effects of plant operation on drifting macroinvertebrates in Lake Michigan near the Ludington Plant. The following aspects were studied: 1. Species composition and relative abundance 2. Spatial and temporal distribution of macroinvertebrates 3. Entrainment into and release of macroinvertebrates from the upper reservoir 4. Survivorship associated with turbine passage The composition and abundance of that portion of the-macrobenthic community migrating into the water column was studied by five general approaches: (1) Day-night distribution of macroinvertebrates in the water column at various depths in Lake Michigan surrounding the power plant (farfield area), (2) Macroinvertebrate withdrawal from Lake Michigan in the intake canal (entrainment), (3) Macroinvertebrates held in the reservoir, (4) Release rates of macroinvertebrates from the reservoir (extrainment), and (5) Mortalities associated with turbine passage. Major emphasis has been placed on amphipods, mysids and chironomids due to their importance as fish forage organisms. DESCRIPTION OF SITE The Ludington Pumped Storage Facility is located approximately four miles (6.4km) southeast of Ludington, Michigan, on the eastern shore of Lake Michigan. The plant site consists of an excavated reservoir above the power house 2.5 miles (4.02km) long, .75 miles (1.21km) wide and 6 miles (9.7km) in circumference (Figure 1). ~The reservoir bottom is composed of 5 feet (1.5m) of compacted clay, except for a limestone scour pad 1,200 (366m) x 800 feet (244m) directly in front of the upper intake structure. Approximately 18 billion gallons (8.04 x 107m3) of the 27 billion gallon (1.02 x 10°m3) total volume are available for daily power generation. Maximum reservoir water depths range from 97 feet (29.6m) in the south to 112 feet (34.1m) in the north end. Protective appurtenances surrounding the power house consist of two jetties 1,600 feet (490m) long and a 1,850 foot (565m) breakwall built parallel to the shore. The breakwall, constructed of large lime- stone boulders, rises 10 feet (3m) above Lake Michigan and is positioned about 2,700 feet (825m) west of the power house and 1,300 feet (396m) from the jetties. The jetties, identical in construction to the break- wall, are separated by a 1,100 foot (335m) channel, dredged to a minimum depth of 28.5 feet (8.7m). The draft tubes (2 per turbine) for the six Francis-type reversible pump-turbines, each revolving at 112 rpm, open to Lake Michigan 38 feet .uomfioum mwmuOum omossm :Ouwcwoaq .maowumum wcaaaamm oumunouuo>cwouumz .H ouswam MACROINVERTEBRATE SAMPLING STATIONS LUDINGTON PUMPED STORAGE PROJECT LAKE 0.8. 3| MICHIGAN MICHIGAN I \ I BUMMIT M 7°“us PAR“ LAKE “3:31.943 Ll" use LAKE (11.6m) below the surface and extend to the dredged bottom at the 70 foot (21.4m) depth. No screens other than coarse trash racks are present. Six penstocks 1,300 feet (396m) long, increasing in diameter from 24 feet (7.3m) to 28.5 feet (8.7m), serve to transfer water from the turbines to the upper reservoir. Maximum velocity in the penstock is 28f/s (8.5m/s) during generation and 24.6f/s (7.5m/s) during pumping. Data taken in 1972 - 1974 indicate that the only physical-chemical parameters modified by plant activity are turbidity and transparency. Water temperature, pH, dissolved oxygen, alkalinity, and dissolved solids are unmodified by plant Operation (Liston et al. 1976). Physical- chemical parameters indicate the oligotrophic conditions of Lake Michigan near the plant site. Reported values are: pH, 7.8 - 8.5; dissolved oxygen, 9.1 - 14.0 ppm; alkalinity, 104 - 136 ppm; dissolved solids, 170 - 190 ppm; water transparency measured by secchi disc, 0.8 - 7.2m; and turbidity 0.3 - 8.70 NTU (Liston et a1. 1976). Seasonally, water temperature in the near-shore area varies from 4 - 23C with temperature variations of 10 - 15 degrees within 24 hours associated with upwellings. Patterns of temperature variation are caused mainly by offshore winds. METHODS Macroinvertebrates were taken from tows made to capture pelagic fish larvae. All samples exclusive of mortality were taken with General Oceanics 1.0m conical plankton nets of 350v NitexR mesh. General Oceanics (Model number 2030) flowmeters equipped with low speed rotors were mounted 1/3 off-center to minimize turbulence vortices created by the tow bridles (Tranter and Smith 1968). Four kilogram.brass depressors were attached to the tow bridle eye to plane the nets. A one liter, 350v mesh windowed, collection bucket was affixed to the net end. The sampling year was apportioned into three periods found to generally coincide with climatic changes in the study area: spring, 1 April - 1 June; summer, 2 June - 31 August; fall, 1 September - 1 November. All entrainment, extrainment, farfield and reservoir meter net collections were preserved in the field in a solution of 10% formalin to be picked in the laboratory. All samples were picked in both black and white benthos pans. Complete removal of organisms was ensured by use of lighted magnifiers (10x). After organism removal, samples were concentrated in 121ml bottles and retained in 75% isOpropyl. Approx- imately ten percent of these retained samples were picked a second time to gauge picking efficiency. In the laboratory specimens were identified, sexed, counted, straightened and measured to the nearest millimeter. A random sample of 9 a maximum of twenty individuals for a specific taxon was drawn from each field collection for analysis, with each size frequency class represented in pr0portion to its dominance. Mysids were measured from the tip of the rostrum to the tip of the telson. Males and females smaller than 7mm were indistinguishable. Amphipods were measured from the base of antennae 1 to the tip of the uropods. Lengths for aquatic insects were taken by measuring from the most distal portion of the head capsule (excluding antennae) to the tip of the abdomen. Macroinvertebrates were identified with the aid of an Olympus variable power binocular microscope using either 10 or 20x oculars. Pontgporeia, Mysis and Oligochaeta were identified using keys presented in Pennak (1978). Gammarid amphipods were identified to species following Holsinger (1976). Aquatic insect identification followed Merritt and Cummins (1978) and Hilsenoff (1975). Identified invertebrates were preserved in a solution of 752 ethanol with glycerin and retained. Farfield Farfield sampling to determine organism abundance and species com- position in Lake Michigan was accomplished by biweekly sampling at four stations (Figure 1). Stations 1 and 4 were located approximately 4.8km south and north of the plant breakwall. Stations 2 and 3 were .8km south and north of the breakwall. Substrate type at each of the sample stations was analyzed on 30 June by making random casts with a ponar grab on a transect at stations 1 - 4 extending outward from shore to the 40 foot (12.2m) .contour, coupled with scuba observations at stations 1 and 2. Substrate type was described in order of decreasing percentage dominance. Station 10 1 displayed a gravel swash step near shore followed by a band of coarse sand interspersed with gravel or cobble-sized stones extending lakeward to approximately the 10 foot (3.0m) contour. Substrate type shifted to fine sand with some gravel roughly extending to the 35 foot (10.7m) contour. Hardpan clay outcroppings with some fine sand patches were encountered lakeward of the 35 foot (10.7m) contour. Station 2 was found to be composed of coarse sand with patches of cobble to a depth of 10 feet (3.0m), followed by fine sand with some large rock beds extending to 20 feet (6.1m). Hard clay overlain with a thin layer of detritus interspersed with rock beds was encountered to 40 feet (12.2m). Station 3 substrate was composed of coarse sand and fine gravel from.shore out to 15 feet (4.6m). Fine sand with scattered large boulders dominated to 30 feet (9.1m), with hard clay and sand patches encountered thereafter. Station 4 evidenced coarse sand with some fine gravel near shore, extend— ing to the 30 foot (9.1m) contour. Hard clay outcroppings overlain with sand patches were encountered out to 40 feet (12.2m). However, the near- shore zone is a highly dynamic environment, with major substrate altera- tions associated with seasonal climatic variations. Bar formation and banding of sediments are a consequence of sediment sorting, which occurs primarily during summer. Fall and winter storms tend to scour the wave- zone as does winter ice cover. In spring, after ice cover is removed, these coarse sediment zones and bars are much less distinct. Day and night samples were taken consecutively beginning mid-April through October and consisted of five minute duplicate stepped oblique tows made at the 10 (3.0m), and 20 (6.1m), 30 (9.1m) and 40 foot (12.2m) contours for each series from the RV Ebbert L. Sampling commenced approximately 0930 - 1500h for day tows and between 2100 - 0130b for night 11 tows with sampling station sequence randomized over the season. Two replicate 5-minute tows per station were made at the five foot contour using an aluminum sled mounted meter net that allowed maximum clearance of 11 inches when towed over the bottom (Figure 2). All nets were washed- down by bucket or pump. Boat speeds for all farfield tows varied as a function of ambient wind and current direction but normally approached 1 knot. A finite area was delineated in Lake Michigan surrounding the power plant to provide a comparison with entrainment estimates. Macroinverte- brate estimates within the rectangle were based on night farfield organism densities since entrainment would only occur at night. This rectangle had a width from the shoreline lakeward to the 45 foot (13.8m) contour (approximately 2.4km) and extended three miles north and south (9.7km total) of the plant. The volume of water contained within this area was estimated to be 188,499,840m3 which is approximately six times greater than the nightly average of water moved (approximately 35,000,000m3) between Lake Michigan and the upper reservoir. Estimation of the volume contained within the rectangle was obtained using a naviga- tion chart (number 14907) with soundings corrected to current lake ele- vations (1979), and a polar planimeter. Contour tows made from the RV Ebbert L. were centered between con- tour intervals for calculation purposes. For example, tows made at the, 10 foot (3.0m) contour were used to represent all water from the 5 foot (1.5m) to 15 foot (4.5m) contours; tows at the 20 foot (6.1m) contour represented all water from.the 15 foot (4.5m) to the 25 foot (7.5m) contour. This technique was continued to the 45 foot (13.8m) contour. .Macroinvertebrate densities from the shoreline to the 5 foot (1.5m) 12 .HSOucou an.“ onu um mafiaaamm pow tom: boa scuxcmaa oonomuum :ufia omam snowesam mnu mo wowsmuo ofiumaonom .N shaman 14 contour were estimated from tows made at the 5 foot contour. Numbers of organisms in the rectangle were estimated using combined station density estimates per l000m3 at discrete contours and extrapolating to the total volume of water contained within the contour interval. These contour interval estimates were then summed to obtain point estimates for sample dates of the total number of organisms estimated to be contained within the rectangle. These values were used as a basis for comparison with macroinvertebrate entrainment estimates on corresponding dates. Entrainment - Extrainment Entrainment samples were taken within the confines of the power plant jetties in an area where current velocities averaged 1 knot (Figure 1). Sampling technique consisted of two series of four sequential stepped oblique tows, each of 5 minutes duration taken at 0200 and 0500h to compensate for variable pumping rates during the pumping mode. The biweekly sampling schedule was initiated in mid-April and continued through the end of October when fall storms forced termination. Estimates of organisms pumped into and released from the upper reservoir were made in the following manner. The total number of organisms obtained for a taxon from the quadruplicate tow series was divided by the sum of the four volumes strained for that series, yielding a mean density for the time period sampled (#lma). The volume of water passed through the plant for the sample period was calculated from reservoir elevation records provided by Consumers Power Company. The invertebrate entrainment estimate in each time period was cal- culated by: Ne 3 DV (1) 15 where Ne - estimated invertebrate entrainment in a time period D - density of macroinvertebrates (#/m3) V = volume of water passed through the plant (m3) The number of macroinvertebrates entrained or extrained during an opera- tional mode was estimated by: m N-EN (2) t t-l e,t and by direct substitution from equation 1 m n-znv (3) t '311:: where Nt - total entrainment for the sample day density of macroinvertebrates in the tth time period volume of water moved in the tth time period U I < I m - number of sample periods for the day The total number of organisms entrained annually was estimated by: P N d t . N a}: —(£ V) (4) TE c-1 Vt 1-1 1 where NTE - annual estimate of macroinvertebrates entrained Nt. - total number of macroinvertebrates entrained on a sample day from equation 3 V - total volume of water moved on a sample day V - volume of water on the 1th day of the sample period d - number of days in sample period P - number of sample days in year Use of this model necessitates the assumption that macroinvertebrate density and vulnerability to turbine passage are similar throughout the sample period to allow calculations. The ratio of the organisms entrained to the volume of water pumped was used as the midpoint for the interval between entrainment sample dates and was multiplied by the volume of water 16 pumped on each date in the interval between sample periods. For example, the ratio of entrained organisms to volume of water pumped on 1 May was used to estimate entrainment for the period 15 April through 8 May. These products were summed to yield the estimate of organisms entrained during the sampling year. Extrainment samples and estimates were made similarly on the generating mode during daylight and night to obtain data on organism release rates from the upper reservoir. Organism release rates during darkness were determined from limited tows made from 2100 - 2200h. Man- power constraints limited the number of dates sampled. Most samples were taken during 1000 - 1300b and 1500 - 1830b. Reservoir Reservoir sampling was initiated in an effort to obtain information on residence times and day-night distribution of organisms in the reservoir. Sampling consisted of two series of five minute duplicate stepped oblique tows made at two north-south stations in the reservoir on dates when entrainment and farfield tows were made (Figure 1). Mortality Survivorship of invertebrates cycled through the power plant was estimated from net tows made between the jetties and at a control station south of the plant. The sampling gear and technique employed was chosen to subject captured organisms to minimal stress inducing conditions i.e. mechanical buffeting and temperature elevation. A 2.0m 350u mesh plankton cone net employed in a slow vertical tow appeared to give best results based on pilot studies done in 1978. In 1979 quadruplicate samples were 17 obtained between the jetties on pumping and generating modes and at the 30 foot contour control station (south). Samples were immediately returned to the laboratory and picked, using lighted magnifiers over black and white benthos pans. Live organisms were transferred to aerated aquaria at ambient lake temperature and held 24 hours for latent mortality determination. In 1980 sampling in the reservoir was eliminated because plant impacts were based on the number of viable organisms returned to Lake Michigan, (organisms entrained into the reservoir were assumed to be "lost" to the Lake Michigan system until released during the generating mode). A series of six samples were taken in generating currents emanating from the plant. The control samples were taken at night, three each at both a shallow (1.5m) and deep (9.1m) site to both minimize avoidance and sample when greater numbers of organisms were assumed to be concentrated at the sample site. The shallow control samples were taken with a 1.0m sled-mounted net. A model developed to estimate ichthyoplankton losses was used to determine macroinvertebrate losses due to plant operation (Liston et a1. 1981). Macroinvertebrates lost were those organisms removed from Lake Michigan either remaining in the reservoir or killed when cycled through the pump-turbines. The number of macroinvertebrates lost was estimated by: N2 =- NTE-{NTX [1 - (Mg - Mcfl} (5) where N, a number of macroinvertebrates lost NTE . number of macroinvertebrates entrained from.equation 4 NTX - number of macroinvertebrates extrained from equation 4 Mg a mortality factor on generation mode and M = mortality factor at control site C RESULTS Farfield Night sampling in the area of Lake Michigan immediately surrounding the power plant was initiated on 16 April and ceased 25 September. A total of 397 samples were taken on 11 dates in 1979 (Table 1). Spring storms delayed the initiation of day sampling until 15 May. A total of 342 samples were collected on nine dates. Macroinvertebrate organisms frequently identified in sample tows were chironomids, Mysis relicta Loven, Pontoporeia hoyi Smith, Gammarus pseudolimnaeus Bousfield, Gammarus fasciatus Say, and the naidid oligo- chaetes Stylaria‘gp;_and'Ngigugp; ‘Less frequently collected taxa were Ephemeroptera, Plecoptera, Trichoptera, Ceratopogonidae, Chaoboridae and Tubificidae. Farfield macroinvertebrate collections were dominated in order of decreasing abundance by Mysis relicta, Pontoporeia hoyi, Chironomidae, Gammarus pseudolimnaeus, naidid oligochaetes, Heptageniidae, Siphlonuridae, Gammarus fasciatus, Perlodidae, Hydropsychidae and Ceratopogonidae. Chironomid larvae predominated in day tows in spring. Low numbers of Mysis relicta and naidid oligochaetes were taken during daylight, while no amphipods were collected. Pontoporeia hoyi, Gammarus pseudolimnaeus, Chironomidae and Mysis relicta were the predominant occurrents in spring farfield night tows. 18 19 mu no em co aw ham «cm HmuOH o OM\OH m c o w o: co mN\a Na wN\m n q o m on on 5N\w q o o w an on mH\w 3 gm m q c w an oq Hm\m m q o m co co o~\m 1» m? o q o m oc mm wN\o NH ~N\o m N c m «N am ~H\o Na n\© o o c m o: mm @N\n m ¢N\m q o c m an oq m~\m NH an NH o w 5N H\m n mm ou\q muwamuuoz uooacwmuuxm umwwz hon uaoscumuuam unwaz hon mama uwo>ummom anwwnuwz oxma .uaoam mwmuoum ooaadm souwcaooa as» am anafi ca amxmu moanfidm oumuoouum>Cwouuma mo Humans tom .mdowumuoa .moumo mafiaeamm .H manna 20 Perlodids, Siphlonurids and Heptageniids were infrequently collected in spring samples. Chironomids and naidid oligochaetes were the most frequently collected taxa in summer day tows. ‘My§i§_dominated night collections, followed by Chironomidae, Pontoporeia hoyi, naidid oligochaetes and Gammarus spp. Fall collections were dominated by Chironomidae, Mysis relicta, Pontoporeia hoyi, Naididae, Gammarus app. and Heptageniidae. Entrainment A total of 89 biweekly collections were made from mid-April through October to outline macroinvertebrate entrainment during field sampling in 1979 (Table 1). Taxa encountered in entrainment samples in order of decreasing abundance were Mysis relicta, chironomid larvae, Amphipoda (Gammarus sp3, Pontoporeia sp.), Oligochaeta (Naididae, Tubificidae), chironomid pupae, Ephemeroptera (Siphlonuridae, Heptageniidae, Ephemeri- dae), Chaoboridae, Isopoda, Plecoptera (Perlodidae) and Trichoptera (Hydropsychidae) (Table 2). Mysis relicta composed nearly 812 of the estimated total macroinvertebrates entrained during sampling in 1979. Chironomids, amphipods and oligochaetes composed approximately 12, 4 and 22 of total macroinvertebrate entrainment, respectively. Entrained amphipods were identified as PontOporeia hoyi Smith, Gammarus pseudolimnaeus Bousfield and Gammarus fasciatus Say. Oligo- chaetes identified in entrainment samples were the naidid oligochaetes Nais sp. and Stylaria sp. and occasionally members of the family Tubificidae. Taxa encountered sporadically in samples were Ephemeroptera (Isonychia sp., Heptagenia sp., Ephemera sp.), Plecoptera (Isoperla sp.), 21. _ N: n :u an. an EN a: = a: a: « acqa~§ ooo.on_.n nn~.n«o._ onc.osn.~ oka.mau ago-eautumm . is. o o o o o o o o «an.oc o o o onuaouuussa cease o nso.oe~ oso.oo~ o «la.an _-.¢_~ moo... «aa.oa o o c o euuocouasu c o o o a o o o o c o o-._n equate-ass» a c o a o o nn~.on nn~.ac «no.4 aun.ck o o - o-vauoso-eu o o o o o o o o o o «ca._~ o-._n «unavouuum o o n_o._m noo.loe.a o o o-.~a s-.e¢n “no.o_e o aus.n~ a «nagging nom.oo o o o o o o o o o «n..cn a «cousconouaon a noo.as o a o o o o o o o o seasons o o o «ca.no o o o can.kn o o ace.- ooa.aa_ occupaaoanaum o o o o o o o -~.nc o a oka.nk a-.~n oauaeoaoaoueaa adomcawmovaflm o ne~.ks_ .na.no an“... o o onh.o« can.~n nan.oo_ o o “no.5“ nataaaao asuauuuou o mne.oc_ ~n~.non o nan.~o nan.oe c sen..o o c o o nauuaaau «no: «Nn.nn_ can.no~ o «54.5co n_o.o~c o nn~.on «al.5n ann.n~ o oo~._o Nuk.o_— «autou0ucoa ona.on~ c~—._nn o__.non.. ouc.nnn onn.ann “an..n_ can.ak~ ._o.n~o oem.eoo ans.c~k.l som.-~.~ «so.no. auaaoaotaau uuuuduu ask.¢~u nan.oao._ ~n¢._~o.e~ eo_.o_o.~ nn~.n_o.hn a~o.o~c.¢a loo.~no.n ~sn.neo .hs.ckn.~ .so.on o_~._a_ noe.aa~ can»: aNuanwaqnllnnumuumwnnINNNMuNu” a~\n~\u m-.n\k «ANS—x“ wswmweo «A\~_\o ok\o~\n ohxnaxn AN\_\A ak\o_\s .mnma wcfiuso mount oaaamm so ufio>uomom mwmuoum omoasm couwswosa onu ca omaamuuco moumunmuum>afiouoma mo assess: omumawumm .N mHan 22 Isopoda (Asellus sp.) and Trichoptera (HydrOpsyche sp.) Nearly all taxa were captured in higher numbers during the first sample period (0200h) throughout spring, except on 15 May when all taxa were collected during the second (0500h) sample period (Table 3). With the exception of Mysis all taxa continued to be collected in higher numbers during the first sample period throughout summer and fall (Table 3). Macroinvertebrate entrainment ranged from the low on 16 April (895,979) to a peak occurring on 1 August (38,458,611; Table 2). The 1 August peak was caused by a marked increase in entrained mysids which comprised nearly 662 of the total entrainment value. Total macroinvertebrate entrainment increased during summer sampling. Peak total entrainment occurred on 1 August, with secondary modes on 10 July and 27 August (Table 2). High entrainment estimates on these dates were mainly due to marked increases in numbers of entrained.My§ig, Fall samples indicated a decline in total entrainment. All taxa I entrained during fall sampling appeared to be decreasing with the excep- tion of heptageniid mayflies (Table 2). Over 602 of entrained macro- invertebrates in fall samples were indicated by the peak value for entrained chironomid pupae occurring on 25 September. Reservoir A total of 74 collections were made in the Ludington Pumped Storage Reservoir in 1979 (Table 1). Night sampling resulted in 34 samples on 9 dates. Day collections totaled 40 samples on 10 dates. Major taxa en- countered in order of decreasing abundance were Chironomidae (larvae), 2:3 .. I. I. I. u. u. I. .n o In I. a I. .. nu N o c o o o a noo.oo a a o o o NAN.ONN NNn.Nn_ NNN.NNN a NN\on\c_ o .N..NN a a o c a o o o NNN.NN «no.Nn .cN.No_ .oN.No_ NNN.Nnc._ N c NNN.NNN o o o o a «No.Ne o o oNN._n on_.¢N ooN.NoN NNN.NN NNN.NNS N NNNNNNN c «N_.NN a a o o o a c c o o qe~.NNN o can.meo N o NNN.NN_ o o o N_N..n o o o a NNN.noN NNN.NN .NN.N¢N o non.onn _ NNNNNNN o o o c o ooc.noN.. o o c o o o o NLN.NN coo.o_c N o c c o a oo_.oN_ o o .Noa.no o a NAN._o NNN.NNN omm.eNN on.Noc.N _ NN\N_\N o o o o c o o o o o o o n_o.NN «AN.NNL onN.NNo.N_ N o N.N.NN o o o a o o a o NNN.N¢ o NNN.oN one.NNN NNN.NNN.N_ _ NN\_N\N o NNN.oo_ o o o a a o o o o o c o N_N.NNs.o_ N o .NN.N¢ a o o o o o o o non.oc o NNN.NN_ o n_a.oan.n _ NNNoNNN o NNN.NN a a a NNN.NN o o o o o o NNN.NN c N_N.oNN.N N c ANN.oc o NNN.NN .o coo.nn c o o o o ANN.o¢ Noa._oN NNN.NN cen.sNN._ _ NNNNNNS o NN_.NN o o o o o o ooN.NN a o NNN.NN Noc.NsN NAN.NN «oe.NnN N o ANN.NN o NNN.N. o .NN.NNN o a o NNN.N¢ cen.NN o _.N.oon c Nn_.ooe a NN\N_\N o o o Nno.e a o a o o c o Nna.c o NNN.NN NNN.NN_ N NNN.NQ o o o o ana.c_c o a o o c NoN.qo~ can.sao o oeo.ooN._ . NNNNNNN o c o NNN.oN a a o o o o o o No¢.eNN._ a .Ns.oN N c o o o a c o a o o o o a a o _ NN\N_\N a a o o a a o a o o o o oNN.Ncn o aeN.oN N o c a o No» NNN.NN NN_.oN o NoN.NN oNN.NN a o I NNN.NNN.N NoN._o NoN.oN_ _ NN\_\N II II II II II II II II II II II II II II II N o c NNN NN o NNN.NN o o o ooo.ua~ NNN..N a Nno.NN eco.no_ NNN.N__ NcN.NNN _ NN\o~\s voNuom one: 6 .u .s a. he a a. aw z .m MN . N my N h» .1ea. 9 M. N N .. u a w . N m . a» .r h... ”M. 0 I am. 8 \l % O O J 00 O O A. .% .n .N An N. a. a. % hm. rm a. 2% N... m x v p. m. . a. .m a. mu Aw m. pm e N». D. 3 NW 6 ” W '0. a I a a O W magnet uao>uommm omeOum omefiam .NNNH aN meoNNma oNaamm ANS cone New ads ooNo was seawawong usuaw owcfimuuam mmumunmuum>awouomfi mo nonaaz .m manme 24 Mysidacea and Naididae. Minor taxa collected in reservoir tows were Pontoporei§_hoyi, Tubificidae, Gammarus pseudolimnaeus, Gammarus fasciatus, Ephemerella sp. and Hexagenia sp. Generally, peak pelagic densities during day collections were recorded in tows made in the north end of the reservoir (Station 9). Highest macroinvertebrate pelagic densities during night tows were noted in collections from the south end (Station 7). Extrainment Sixty-nine samples were taken on ten dates during the period May through September to outline macroinvertebrate release rates from the Ludington Pumped Storage Reservoir (Table 1). Taxa encountered in extrainment samples in order of decreasing abundance were Chironomidae (larvae and pupae), Mysis relicta, naidid oligochaetes, gammarid amphipods, tubificid oligochaetes, PontOporeia hoyi, Isopoda, Siphlonuridae (Ephemer- 0ptera), Heptageniidae (Ephemeroptera) and Hydropsychidae (Trichoptera) (Table 4). Chironomid larvae and pupae composed 32.5 and 25.42 of extrained macroinvertebrates, respectively. Approximately 202 of the invertebrates returned to Lake Michigan from the upper reservoir were ‘Mysis relicta. The amphipods Pontoporeia hoyi and Gammarus app. con- tributed 2.3 and 4.8%, respectively, to the total extrainment estimate in 1979. 25 Table 4. Total number of macroinvertebrates estimated to be entrained and released at the Ludington Pumped Storage Reservoir during sampling in 1979. Taxon Entrainment Extrainment Mysidacea Mysis relicta 1,295,101,546 67,092,310 Chironomidae Chironomid larvae 168,992,283 109,457,724 Chironomid pupae 19,427,860 85,485,209 Amphipoda Pontoporeia hoyi 34,807,055 7,805,142 Gammarus spp. 29,217,664 16,230,582 Oligochaeta Naididae 37,437,472 32,545,127 Tubificidae 599,556 8,932,065 Ephemeroptera Siphlonuridae 4,817,272 3,450,751 Heptageniidae 3,604,282 1,407,312 Ephemeridae 462,243 0 Diptera Chaoboridae 2,435,176 0 IsOpoda Asellus sp. 1,083,813 4,062,550 Plecoptera Perlodidae 739,004 0 Trichoptera HydrOpsychidae 2,176,638 65,103 Total Invertebrates 1,600,901,864 336,533,875 26 Mysis relicta Farfield Few My§i§_were captured in day tows during spring sampling (Figure 3). All Mysis were captured on 29 May at the 20 (6.1m) and 30 foot (9.1m) contours at stations 2 and 4, respectively. These individ- uals were all immature (1 - 5mm). .Hlflifi distribution during night sampling in spring exhibited a trend of lakeward increase at all stations. Lowest overall densities occurred at stations 1 and 4 (Figure 3). Greatest concentrations of mysids were noted at the 30 (9.1m0 and 40 foot (12.2m) contours at stations 2 and 3. Peak concentrations 0f.Hl§$§ occurred on 16 April when densities of-344/1000m3 and 204/1000m3 occurred at the 40 foot (12.2m) contour at stations 2 and 3, respectively. Nearly 922 of the Mysis estimated to be contained within the rectangle were distributed at this contour (Table 5). .Mygig captured on this date were mostly subadults, with some adults in reproductive condition noted at the 10 (3.0m) and 20 foot (6.1m) contours. .Mzgi§_were seldom captured in day tows made during summer (Figure 3). The majority of organisms captured were collected at the 30 (9.1m) and 40 foot (12.2m) contours. Peak day collections occurred at the 30 foot (9.1m) contour at stations 1 and 2 on 31 July. Relatively few mysids were captured at the shallow contours (<30 ft) during day tows. Most of these individuals were juvenile (<11mm) instars. Farfield night tows made during summer contained numerous mysids. Most Mysis captured at night were taken at the 40 foot (12.2m) contour (Figure 3). Summer sampling revealed highest densities at station 2. 27 .mmaH ad unmam Nosom wwmu0um omeasm couwswvsq may some musouaoo can mcowumum ucmummwfio um muowaou mNmNm mo Amaooo~\.ozv uufimcoo .m shaman 28 in Q 0— ‘ 20:.(5 .m_...r:C:_2 .3. n 20. 7‘; n5 :9 {*5 2 an N: < m « ZO_.—<._.w . TSP: 3r: _ 20. .25 :00— :00N :000 :00? ¥00n .000 .005 29 NNN.NNN.NQN NNo.NmN.on oNo.NmN.NoH «mm.NNN.N lNN.nHN.N NNN.NN Nance omm.omw.a omm.oNN.l oHN.~oN NAN.GN Nam.n o NN\NN\N mmo.NHN.NN CNN.GNN.NL NoN.NNl.N omo.NNN qu.aN NHL.N NN\NN\N NNN.NON.NN owl.oeN.oN on.oNN.LL NNL.moo.H Nae.oNN o NN\NL\N NNN.NNs.o0m ooN.¢lN.Nos ooe.NNN.NoH mam.NcN.N NNN.oNN o NN\lN\N oom.eNN.NN ONm.oNN.Ne onH.NNN.NN soo.NNN.N www.mem o NN\oL\N NNm.oeN.le oem.oNN.mN NNN.Noq.o NGN.GLN ONN.NN~ oNN.N NN\NN\G NNN.NGG.N Nom.eel.N oNs.moN.N NNN.GNN o mom NN\NH\G NNN.omN.oH NNN.NNo.N ANN.NNN.N qu.HNH «mm.sN NNN.H NN\NN\N «NN.NNN.N NmN.mNN.N mms.mnn NNN.NN o o NN\NN\N mNN.Nno.H Nel.eeN Nem.oqm Nlo.mN lom.me on.N NN\L\m emN.NHN.NN on.oNN.NL «NL.NNG.N NmN.NNL NNN.GN mmm NN\ol\q Nance as on oN on m mama Sumo: unoucoo .mmmfi :H uamHm uosom wwmuoum omaasm souwaaosa msu you: oawamuomu Hmowuonuommn exn.a x q.~ m a“ mam>uouau uncucoo casuHB toawmuaoo on ou moumawumm muoHHou mama” mo muoaasz .m magma 30 Figure 3 indicates marked density increases occurred at the 10, 20 and 30 foot contours on 28 June. ‘My§i§_densities peaked on 31 July when sub- stantial increases were exhibited at the 40 foot (12.2m) contour at all stations. Nearly all Mysis collected shoreward of the 30 foot (9.1m) contour were juveniles. Few mysids were taken from the 5 foot (1.5m) contour during summer sampling. No Mygig_were collected in daylight fall tows made on 26 September (Figure 3). Low numbers of My§i§_were collected at all stations in night tows with most in the 6 - 10mm length category (Figure 3; Table 5). Entrainment A precipitous decrease in Mysis entrainment occurred on 15 May (Table 6). However, estimates of Mysis in Lake Michigan increased on this date (Table 5). Sampling on 29 May indicated a significant increase 19.!Zfiifi entrainment. Eighty—six percent of the entrained mysids were immature (<11mm), with most entering the plant during the early portion of the pumping mode (Table 3). Entrainment estimates for Mysis continued to increase over the course of summer sampling to the peak value recorded on 31 July decreasing. thereafter (Table 6). Most (>902) of the Mysis collected during summer were immatures (<11mm), with the majority of these captured during period 1 (Table 3). Adults were captured during the second sampling period (Table 3). Collections of entrained Mysis in fall continued to be dominated by immature instars. However, the percentage in the 6 - 10mm length cate- gory increased. 31 Table 6. Total number of Mysis relicta estimated to be entrained into the Ludington Pumped Storage Reservoir during 1979. Sample Number Estimated Number ' Date Entrained Entrained for Interval Interval 4/16/79 239,403 3,482,266 4/12 - 4/24 5/1/79 191,210 2,426,486 4/25 - 5/8 5/15/79 30,941 487,465 5/9 - 5/22 5/29/79 1,874,471 23,232,258 5/23 - 6/5 6/12/79 645,562 10,600,408 6/6 - 6/20 6/28/79 3,651,061 41,754,522 6/21 - 7/4 7/10/79 14,020,628 204,603,313 7/5 - 7/21 7/31/79 37,613,133 850,603,482 7/22 - 8/8 8/15/79 2,619,164‘ 42,372,312 8/9 - 8/21 8/27/79 14,021,452 48,312,617 8/22 — 9/11 9/25/79 1,686,345 38,317,365 9/12 - 10/12 ‘10/30/79 814,748 28,909,052 10/13 - 11/12 1,295,101,546 4/12 - 11/12 32 Reservoir Mysis relicta was not collected in day tows until 28 May when peak numbers were recorded at station 9 (Table 7). Densities recorded in day tows ranged from 0 - 908 organisms per 1000m3 of water. Highest daytime densities occurred at station 9, with the exception of the 28 May sample date. .My§i§_were collected in night tows at the inception of sampling. Densities 0f.!2§$§ ranged from 3 - 1292/1000m3 at stations 7 and 9. Peak reservoir density occurred on 27 August. Higher pelagic densities reg- ularly occurred at station 7 during night sampling. Extrainment Estimated Mysis release was highest at initiation of extrainment sampling on 1 May (1,830,218). Adult and subadult instars (6 - 10 and 11 - 16mm) dominated in collections made on this date (Table 8). Release rates of Mysis from the reservoir declined throughout the remainder of spring sampling. Extrainment estimates averaged approximately 592 of entrainment values during spring collections. ‘Mygig released from the pumped storage reservoir varied sub- stantially. Interval estimates of extrained organisms ranged from 0 on 28 June to 47,647,715 on 15 August. An average of 282 of entrained mysids were estimated to be returned to Lake Michigan during summer sampling. Mysis extrainment declined substantially in September from late summer values (Table 8). The extrainment estimate on 26 September represented .82 of the estimated number of organisms entrained during the previous night. All of the extrained Mysis released on this date were 6 - 10mm individuals. 33 Table 7. Mean densities of Mysis relicta (#/1000m3) in samples from the Ludington Pumped Storage Reservoir during 1979. Total Reservoir Station 7 Station 9 Density Date Day Night Day Night Day Night 5/10/79 0 -- O -- 0 --- 5/15/79 0 271 0 --- 0 271 5/28/79 0 432 908 73 454 252 6/12/79 0 258 0 134 0 196 6/28/79 .5 256 0 219 2 238 7/10/79 6 868 16 103 11 486 7/31/79 0 992 78 3 39 497 8/15/79 0 31 0 340 0 185 8/27/79 0 1,292 0 285 0 788 9/25/79 0 247 2 247 1 247 34 Table 8. Total number of Mysis relicta estimated to be released from the Ludington Pumped Storage Reservoir during 1979. Number Estimated Number Date Extrained Moved for Interval Interval 5/1/79 1,830,218 3,710,346 4/25 - 5/8 5/15/79 0 0 5/9 - 5/22 5/29/79 47,560 526,786 5/23 - 6/5 6/12/79 196,023 5,420,153 6/6 - 6/20 6/28/79 0 0 6/21 - 7/4 7/10/79 408,816 5,050,069 7/5 - 7/21 8/1/79 162,822 2,854,612 7/22 - 8/8 8/15/79 3,919,013 47,647,715 8/9 - 8/21 8/27/79 99,924 1,613,883 8/22 - 9/11 9/26/79 12,856 268,747 9/12 - 10/12 67,092,310 4/25 - 10/12 35 Losses to Lake Michigan As stated previously, Mysis losses to Lake Michigan were estimated from equation 5. The entrainment estimate for the 1979 sampling year was 1,295,101,546 (Table 6). The corresponding extrainment estimate for mysids was 67,092,310 (Table 8). Chironomidae Farfield Chironomid larvae dominated farfield day collections in spring. Few chironomids were captured in day tows in comparison to night collections. Chironomids were generally collected at the 10 (3.0m) and 20 foot (6.1m) contours during spring sampling (Figure 4). Highest density (31.2/1000m3) occurred at the 20 foot (6.1m) contour at station 1 on 29 May. Chirono- mids were occasionally sampled at the 5 (1.5m) and 40 foot (12.2m) contours in daylight. Chironomid larvae were collected at all stations when night tows were initiated on 16 April (Figure 4). Catch per effort was higher in night tows versus day tows. Peak pelagic densities occurred at the 10 foot (3.0m) contour (5990/1000m3) at station 1 and the 5 foot (1.5m) contour (2555/1000m3) at station 4 during May sampling (Figure 4). However, most pelagic chironomids were distributed lakeward of the 20 foot (6.1m) contour (Table 9). Numbers of chironomid larvae in the water column exhibited a general shoreward increase as spring sampling pro- gressed until 15 May, declining thereafter. Overall, night larval chironomid densities in spring appeared to be greatest at station 2. Diamesa sp., Chironomus sp., Eukieferiella sp. and Glyptotendipes sp. 36 . a new meow%Mwm HGWHMWMNWQMMmmMWMMMum tuneup aouwaaoau baa umoa muscuaoo omoaaoaouanu mo A Boo . N o~\ ozv huwmamn .q snow , Ah 37 v 20_ 70.5 n ZO:.<._.m << m 20:<._.w 2 _ 2024.; 38 NNN.oNl.Nm¢ «No.Nom.eoN «NN.NN¢.oNL oeN.NNN.NN NNN.NSN.NN Nao.NNl.N Nmuoa NNN.NNN.N oNN.eNN.N Noq.NNm LAN.lNN NAN.¢NN NNN.SHN NN\NN\N qu.ooN.NH NNN.¢NN.N loN.mNN.N Noe.ona.s ooe.NNN NNN.NNN NN\NN\N NNq.oem.Nl NAN.NHG.N oNN.NNN.oL NNN.Noo.N Noe.ooN NNN.NeN NN\NL\N «NN.ONN.NN omo.NHN.NH oLN.oNN.NN «NN.sNo.N omo.oNN.ll NoN.HNN NN\H\N ANN.NNo.o NNN.NNN.N NNN.GNN NNm.eNl NoN.NsN Nae.om NN\oL\N Nae.omn.mm ooN.Noo.NN mwa.ome.m ooe.NNN NN_.NNN NNN.om NN\NN\G NAN.NNN.NN oNN.eNe.NN mme.Lea.N NNN.eoN.s NoN.oNN NNN.nel NN\NH\© NHN.NNo.ao omN.on.Nm ooN.Nmo.NH NNN.NNe.L NGN.NNN NNN.NNN NN\NN\N NNN.oNN.NNL on.NNN.No oNN.emL.ls all.NeN.Nl oeN.NmN.oN Noa.soe NN\NN\n oNo.oNN.o omm.smm.m SNN.GNN.L mmm.NNN NMN.NNo.N «so.NNN NN\N\N Nlo.mNH.om oNe.mme.oe ANN.NNN.N oNN.eoN ANN.NoH NNN.N NN\NL\N Nance ON on oN on m canon Noouaou .mnmfi :N uamHm umsom ommNOum toaasm aouwawoaa mag some mamemuumu Hmowumnuoahn sxn.m x c.~ m aw mam>uouaw usousoo away“: oonwmuaoo on ou voumawumo mmofiaoaouwnu mo muomaaz .m manna 39 were identified most often in spring samples. Tanypus sp., Procladius sp. and Chironomus sp. dominated collections made at the 5 (1.5m) and 10 foot (3.0m) contours. Eukieferiella sp. was most abundant at the 30 (9.1m) and 40 foot (12.2m) contours. Chironomid pupae were first collected in spring day tows on 29 May. Greatest concentrations of pupae were recorded at the 5 foot (1.5m) and 10 foot (3.0m) contours (Figure 5). Farfield night tows collected chironomid pupae at station 1 at the 5 (1.5m) and 10 foot (3.0m) contours on 15 and 29 May, respectively (TablelO). Daylight sampling in the farfield area during summer (June - August) revealed that most larval chironomids were distributed in the water column shoreward of the 30 foot (9.1m) contour (Figure 4). Overall, larval chironomid densities were greatest at station 2 during day sampling (Figure 4). Night tows made during summer captured chironomid larvae at all stations and depths (Figure 4). Pelagic densities peaked in late July and early August shoreward of the 20 foot (6.1m) contour. Peak pelagic larval density (1798/1000m3) occurred at the station 1, 5 foot (1.5m)_ contour on 27 August (Figure 4). Chironomus sp. and Crytochironomus sp. were most abundant in samples. Most larvae were estimated to be distrib- uted at greater depths (>20 ft) as evidenced by collections made at station 3, 40 foot (12.2m) contour when tow densities of 1215/1000m3 were noted on 28 June. These samples contained many Eukieferiella sp. Farfield day tows made during summer revealed numerous concentra- tions of chironomid pupae in the water column. Overall, peak chironomid pupal densities occurred at station 1 (Figure 5). Densities increased as summer sampling progressed until 31 July when no chironomid pupae were 40 can Mwmwuwwmuwmwm umsom owmuoum ooaaam couwafioaq onu Home muscuaou ommwo an ocean ofieoaouwso mo Aneooo~\.ozv muwmcmo .n madman 41 .0? b .0N .0n Duh-Dhbb .0. = O 80....(hm n 3.h(hm N 20....‘hm . 20....(bm E.— .nn(.. .. 3(m(.... 3(m1bn—H_N3Nb(—m_M_—N. n—NIN—(O an H— C F— r 100 I00. _v. . ran. a N N N N N N N N N I r c = I u . .ooN NO I I a . bLmIN h N N} I r I t I 1 .- \Vo . o4 t / v 4V. . J x I v ‘04 . o/ T 00 r av r- ’0 y I .90. 42 oea.NNm.HN oNN.NNN.N NNN.NNN.N NNN.NNN NoN.NmN NNN.NN Nmuoa NNN.NN meo.om o NLN.NN NNN.NN ANN NN\NN\N NNN.NNN.N NNN.lNo.N cam.oom NNN.NoN «No.eN o NN\NN\N Nmm.ooe.l Nom.moN NoN.NNN.l o Noo.NN NNN.N NN\NN\N NNN.NNN.N NSN.NNN.L NNN.NNN NNN.NN o o NN\HN\N NNN.ooN NNN.NNN «No.3eN NNN.¢N NNN.NN NNN NN\oN\N NNN.NNN NNN.NNH NLN.NN Heq.NN o NNN NN\NN\N . ooe.NNN NNN.NNN «0N.oml o o o NN\NN\N NNN q o o o NNN.N o NN\NN\N . NNN N o o o o NNN.N NN\NN\N o o o o o o NN\l\m o o o o o o NN\NN\N Nance c. on oN. oN m comma Noouaou .mmaw “Huuamam nosom omMNONm omeasm aouwaaosa onu some oawomuoou Hmuauonuoa%m_axn.m x c.~ a a“ H muaw usoueoo canufia nonwoucou on cu omumawumm Annoumwnv omenm mmoaaoaouanu mo muomanz .o. nanny 43 encountered in day tows. Pelagic pupal densities increased after this date to a second peak recorded on 27 August. Distribution of chironomid pupae in night tows was sporadic. Over- all, highest densities were recorded at the 30 (9.1m) and 40 foot (12.2m) contours (Figure 5). Chironomid pupae were captured at all stations on 27 August. Greatest pelagic distribution of pupae was estimated at the 40 foot (12.2m) contour on this date (Table 10). Chironomid larvae were captured in day tows at stations 1, 2 and 4 during fall sampling (Figure 4). Peak night density (1011/1000m3) occurred on 26 September at the 5 foot (1.5m) contour. Pelagic densities of larval chironomids decreased lakeward. However, estimates of chironomids above bottom increased lakeward during fall (Table 9). Chironomid pupae were captured only in day tows made at the 5 foot (1.5m) contour at stations 1, 2 and 4 on 26 September (Figure 5). Night tows collected pupae at stations 2, 3 and 4, all at densities below those recorded in summer tows. Entrainment Numbers of entrained chironomid larvae peaked in spring samples on the night of 1 May. However, the interval estimate for the period 9 - 22 May yielded the highest value as a function of larger volumes moved (Table 11). Chironomid larvae entrained declined abruptly during sub- sequent spring sampling. Numbers of chironomid pupae encountered were increasing in all areas (Table 10). Entrained chironomid larvae declined steadily from the 12 June value (815,614), increasing again to a peak on 27 August (1,383,116; Table 11). Large numbers of 4th instar Cryptochironomus sp. larvae were noted in 44 Table 11. Total number of Chironomidae estimated to be entrained into the Ludington Pumped Storage Reservoir during 1979. Sample Number Estimated Number Date Entrained Entrained for Interval Interval 4/16/79 165,944 2,413,761 4/12 - 4/24 5/1/79 2,122,569 26,935,728 4/25 - 5/8 5/15/79 1,724,487 27,168,274 5/9 - 5/22 5/29/79 684,540 8,484,211 5/23 - 6/5 6/12/79 815,614 13,392,724 6/6 - 6/20 6/28/79 279,304 3,194,197 6/21 - 7/4 7/10/79 139,377 2,033,929 7/5 - 7/21 7/31/79 338,538 7,655,887 7/22 - 8/8 8/15/79 533,428 8,629,695 8/9 - 8/21 8/27/79 1,383,116 47,656,938 8/22 - 9/11 9/25/79 551,110 12,522,393 9/12 - 10/12 10/30/79 250,958 8,904,546 10/13 - 11/12 168,992,283 4/12 - 11/12 45 samples on this date. Highest larval chironomid estimates in the farfield area during summer were recorded on 1 August (Table 9). Chironomid larvae continued to be taken in greater numbers in summer during the 0200b sample period (Table 3). Numbers of entrained chironomid pupae fluctuated inversely with values for entrained larvae during sampling. Reservoir Chironomid larvae first appeared in day tows on 10 May at station 9 (Table 12). Daytime densities ranged from 0 - 38 organisms per 1000m3 of water. Highest densities consistently occurred at station 9 during day collections. Chironomid larvae were noted in night tows on 15 May (Table 12). Night densities peaked on 12 June at station 7 (3047/1000m3). Station 7 consistently exhibited higher densities throughout reservoir night sampling. Reservoir day collections captured low numbers of chironomid pupae (Table 13). They were noted initially in tows made on 28 May. No pattern of preference was visible during day tows for chironomid pupae. Night tows in the reservoir captured chironomid pupae initially on 28 May. Tow densities ranged from 0 at station 9 on 10 July to the mode of 836/1000m3 which was recorded on 12 June at station 7. Two density pulses were indicated from reservoir collections, one in early June, and another in late July to early August (Table 13). On dates when chironomid pupae were taken in night tows, station 7 repeatedly had higher densities with the exception of tows made on 25 September. 46 Table 12. Mean densities of Chironomidae (#llOOOma) in samples from the Ludington Pumped Storage Reservoir during 1979. Total Reservoir Station 7 Station 9 Density Date Day Night Day Night Day Night 5/10/79 0 -- 18 -- 9 -- 5/15/79 5 874 0 -- 2 874 5/28/79 0 912 38 156 19 534 6/12/79 0 3,047 -— 411 0 1,729 6/28/79 0 89 6 15 3 52 7/10/79 6 58 0 O 3 29 7/31/79 5 135 0 19 3 77 8/15/79 0 406 10 158 5 282 8/27/79 0 1,781 2 346 1 1,063 9/25/79 0 208 0 28 0 118 47 Table 13. Mean densities of chironomid pupae (#/1000m3) in samples from the Ludington Pumped Storage Reservoir during 1979. Total Reservoir Station 7 ‘ Station 9 Density Date Day Night Day Night Day Night 5/10/79 0 r -- 0 -4- 0 --- 5/15/79 0 0 0 --- 0 0 5/28/79 0 0 4 18 2 9 6/12/79 18 836 --- 234 18 535 6/28/79 11 169 0 113 5 142 7/10/79 0 12 6 0 3 6 7/31/79 0 359 0 122 0 241 8/15/79 2 679 0 219 1 449 8/27/79 5 561 8 35 6 298 9/25/79 ‘ 0 8 0 14 0 11 48 Extrainment Spring larval chironomid extrainment peaked on 1 May (8,588,705; Table 14). Extrainment estimates of larval chironomids averaged approxi- mately 312 of entrainment values during spring. Peak pupal release was recorded on 15 May (Table 15). Larval chironomid extrainment remained relatively constant over the summer until 15 August when numbers released exhibited over a ten-fold increase (Table 14). Entrainment rates of chironomids were lower but exhibited the same trend during summer (Table 11). Release of chironomid pupae (Table 15) fluctuated markedly during summer but normally remained substantially below entrainment estimates for summer sampling (Table 2). Extrainment of chironomid larvae in fall decreased to approximately half late summer estimates (Table 14). Release of chironomid pupae was nearly 252 of the entrainment value on 26 September (Table 15). Gammarus spp. Farfield Gammarus spp. were not captured off bottom during spring farfield day collections in 1979 (Figures 6 and 7). No clear trend was apparent in spring farfield Gammarus pseudolime naeus distribution (Figure 6). No Q; pseudolimmaeus were captured in night tows made on 15 May at stations 2 and 4 (Table 16). Peak density of §;_pseudolimnaeus (1092/1000m3) occurred on this date at the 5 foot (1.5m) contour at station 4. All 9; pseudolimnaeus collected in spring tows were mature adults. 49 Table 14. Total number of Chironomidae estimated to be released from the Ludington Pumped Storage Reservoir during 1979. Number EEEImated Number Date Extrained Moved for Interval Interval 5/1/79 8,588,705 17,411,624 4/25 - 5/8 5/15/79 183,748 2,648,674 5/9 - 5/22 5/29/79 148,130 1,640,721 5/23 - 6/5 6/12/79 83,968 2,321,773 6/6 - 6/20 6/28/79 90,800 1,038,996 6/21 - 7/4 7/10/79 419,414 5,180,985 7/5 - 7/21 8/1/79‘ 78,249 1,371,873 7/22 - s/s 8/15/79 3,054,570 37,137,738 8/9 - 8/21 8/27/79 1,782,470 28,788,892 8/22 - 9/11 9/26/79 570,050 11,916,448 9/12 - 10/12 109,457,724 4/25 - 10/12 50 Table 15. Total number of chironomid pupae estimated to be released from the Ludington Pumped Storage Reservoir during 1979. Number Estimated Number Date Extrained Moved for Interval Interval 5/1/79 0 0 4/25 - 5/8 5/15/79 286,793 4,134,028 5/9 - 5/22 5/29/79 87,617 970,469 5/23 - 6/5 6/12/79 340,857 9,424,908 6/6 - 6/20 6/28/79 110,827 1,268,147 6/21 - 7/4 7/10/79 748,984 9,252,139 7/5 - 7/21 8/1/79 0 0 7/22 - 8/8 8/15/79 877,514 10,668,898 8/9 - 8/21 8/27/79 3,034,570 49,011,726 8/22 - 9/11 9/26/79 36,112 754,894 9/12 - 10/12 85,485,209 4/25 - 10/12 51 .mnmfi ca ucmHm Hosom mmeOum omaasm souwawosa on» you: muaoucoo one mcowumum uaouommao um msmwaswaoosommxmaumeamu mo Anaooo~\.ozv Nuamcon .o muswwm 52 N 20.25 .m .24.“.“r2. _< T N n 20:53 can... a 202.5% _._:2__0? r—PNNN——_N NN—NN .....——.N— NFL. _ 4v 1r L Li .v .N Lr _p_— _bNPLN rNNNN-N_N _b_.p__—_. fi L Y / ’0 r l/ .. ., ca 6.0 .. e rs 53 .ammN ca unoam nosom mmmuoum poaeom :ouwowoaa onu have muscuaou new maofiumum uaouomuav um mauowommm maumeamo mo AnacooH\.ozv Swanson .N ousmam 54 V 20:.(hm n 20....(hm mama... N 20:.(bm _m_«_::+z.Fuou:« uncuaoo awauas toawmuaoo on On owumaaumo maumaummm msumaamu mo muomabz .5. manta 58 Entrainment Gammarus pseudolimnaeus entrainment peaked on 29 May (Tables 2 and 18). Peak §g_p§eudolimnaeus farfield density occurred at the 30 foot (9.1m) contour on this date at station 2 (Figure 6; Table 18). Gammarus fasciatus were identified in Lake Michigan tows made at the 40 (12.2m) and 5 foot (1.5m) contours on 16 April and 1 May, respectively, at station 2 in the farfield area (Figure 7). However, no G; fasciatus were identified from entrainment samples in spring (Table 19). Gammarus app. entrainment exhibited marked fluctuations during summer (Tables 18 and 19). Numbers of entrained Gammarus sp. appeared to be increasing in late August. All amphipods were captured in greatest numbers during the 0200h sample interval (Table 3). Numbers of Gammarus spp. decreased in fall entrainment collections (Tables 18 and 19). Most of these individuals were juveniles. Reservoir A total of 15 Gammarus pseudolimnaeus were captured during reservoir sampling in 1979. Most §g_p§eudolimnaeus were collected during night sampling with peak density occurring at station 9 on 28 May (Table 20). Densities were higher at station 9 on dates when E; pseudolimnaeus were sampled. Nine Gammarus fasciatus were taken during night tows made in the reservoir in 1979. Organisms were captured on 15 May and 27 August at station 7 and 9, respectively (Table 21). 59 Table 18. Total number of Gammarus pseudolimnaeus estimated to be entrained into the Ludington Pumped Storage Reservoir during 1979. Sample Number Estimated Number Date Entrained Entrained for Interval Interval 4/16/79 77,657 1,129,575 4/12 - 4/24 5/1/79 0 0 4/25 - 5/8 5/15/79 0 0 5/9 - 5/22 5/29/79 109,555 1,357,824 5/23 - 6/5 6/12/79 37,396 614,060 6/6 - 6/20 6/28/79 40,736 465,864 6/21 - 7/4~ 7/10/79 0 0 7/5 - 7/21 7/31/79 0 0 7/22 - 8/8 8/15/79 61,755 999,064 8/9 - 8/21 8/27/79 93,731 3,229,631 8/22 - 9/11 9/25/79 147,243 3,345,678 9/12 - 10/12 10/30/79 0 0 1 10/13 - 11/12 11,141,696 4/12 - 11/12 60 Table 19. Total number of Gammarus fasciatus estimated to be entrained into the Ludington Pumped Storage Reservoir during 1979. Sample Number Estimated Number Date Entrained Entrained for Interval Interval 4/16/79 0 0 4/12 - 4/24 5/1/79 0 0 4/25 - 5/8 5/15/79 0 0 5/9 - 5/22 5/27/79 0 0 5/23 - 6/5 6/12/79 91,544 1,503,192 6/6 - 6/20 6/28/79 0 0 6/21 - 7/4 7/10/79 40,505 591,093 7/5 - 7/21 7/31/79 42,313 956,880 7/22 - 8/8 8/15/79 0 O 8/9 - 8/21 8/27/79 365,732 12,601,753 8/22 - 9/11 9/25/79 106,638 2,423,050 9/12 - 10/12 10/30/79 0 0 10/13 - 11/12 18,075,968 4/12 - 11/12 61 Table 20. Mean densities of Gammarus pseudolimnaeus (#/1000m3) in samples from the Ludington Pumped Storage Reservoir during 1979. Total Reservoir Station 7 V Station 9 Density Date Day Night_ Day Night Day Night 5/10/79 0 -- 0 -- 0 -- 5/15/79 0 0 O _ --- 0 0 5/28/79 0 8 12 27 6 18 6/12/79 0 9 ’-- 12 O 11 6/28/79 0 0 0 0 0 0 7/10/79 0 0 O 0 0 0 7/31/79 0 0 0 6 0 3 8/15/79 0 0 0 17 O 8 8/27/79 0 0 0 O 0 0 9/25/79 0 0 0 0 0 0 62 Table 21. Mean densities of Gammarus fasciatus (#llOOOma) in samples in the Ludington Pumped Storage Reservoir during 1979. Total Reservoir Station 7 Station 9 Density Date Day, ,Night Day Night Day Nighg 5/10/79 0 -- 0 -- 0 -- 5/15/79 0 18 0 -- O 18 5/28/79 0 0 O O O 0 6/12/79 0 0 0 0 O 0 6/28/79 0 8 0 0 O 4 7/10/79 0 0 0 0 0 0 7/31/79 0 0 0 0 0 0 8/15/79 0 0 0 O 0 0 8/27/79 0 0 O 20 0 10 9/25/79 0 0 0 0 0 0 63 Extrainment Extrainment estimates of Gammarus pseudolimnaeus peaked on 1 May declining thereafter during spring sampling (Table 22). No Gammarus fasciatus were collected in spring extrainment samples (Table 23). Point estimates of numbers of Gammarus pseudolimnaeus extrained in summer ranged from 0 values recorded on three dates, to the summer mode on 15 August (511,498; Table 22). Percentage release of entrained Gammarus pseudolimnaeus exceeded 1002 on all dates except 27 August when no §;_p§eudolimnaeus were estimated to be released. Release rates of Gammarus fasciatus exhibited marked fluctuations during summer (Table 23). .2; fasciatus were taken in entrainment tows on three of six dates yielding estimates ranging from 0 to 3,733,099. Approximately 312 of the g; fasciatus entrained into the pumped storage reservoir were estimated to be returned to Lake Michigan. Extrainment tows made on 26 September collected no gammarids (Tables 4, 22 and 23). Pontoporeia hoyi Farfield No Pontoporeia were captured off bottom during spring farfield day collections made in 1979 (Figure 8). Highest night concentrations of Pontoporeia hoyi occurred at the 40 foot (12.2m) contour (Figure 8; Table 24). Most Pontoporeia appeared to be distributed at station 2, lakeward of the 10 foot (3.0m) contour (Figure 8). Overall, greatest numbers of Pontoporeia were captured on 64 Table 22. Total number of Gammarus pseudolimnaeus estimated to be released from the Ludington Pumped Storage Reservoir during 1979. Number Estimated Number Date Extrained Moved for Interval Interval 5/1/79 595,486 1,207,211 4/25 - 5/8 5/15/79 0 0 5/9 - 5/22 5/29/79 39,958 442,587 5/23 - 6/5 6/12/79 72,112 1,993,947 6/6 - 6/20 6/28/79 136,201 1,558,474 6/21 — 7/4 7/10/79 0 0 7/5 - 7/21 8/1/79 0 0 7/22 - 8/8 8/15/79 511,498 6,218,842 8/9 - 8/21 8/27/79 0 0 8/22 - 9/11 9/26/79 0 0 9/12 - 10/12 11,421,082 4/25 - 10/12 65 Table 23. Total number of Gammarus fasciatus estimated to be released from the Ludington Pumped Storage Reservoir during 1979. Number Estimated Number Date Extrained Moved for Interval Interval 5/1/79 0 0 4/25 - 5/8 5/15/79 0 0 5/9 - 5/22 5/29/79 0 0 5/23 - 6/5 6/12/79 15,667 433,198 6/6 - 6/20 6/28/79 0 0 6/21 - 7/4 7/10/79 0 0 7/5 - 7/21 8/1/79 0 0 7/22 - 8/8 8/15/79 52,903 643,203 8/9 - 8/21 8/27/79 231,136 3,733,099 8/22 - 9/11 9/26/79 0 0 9/12 - 10/12 4,809,500 4/25 - 10/12 66 .mum. ca unmam Nosom mwmuoum ooaaom acuwawosa one Home musouooo mam mcowumum acouomuwo um “No: mamuoeoueom mo Amaooo.\.ozv aufimaon .w ouswam 67 v 202.5% n 202?; a ZO...<..m . ZO..—<..m NNNN. ma... 2uouaw usouaoo aqnufis oocfimuaoo on cu mommaaumo who: mfiouomouaom mo muomeaz .cu manna 69 16 April. Mature males predominated in sample collections made on this date. Most Pontoporeia hoyi captured in night tows during summer near the Ludington Plant were collected at the 40 foot (12.2m) contour (Figure 8). The majority of PontOporeia were distributed at station 1. Numbers of Pontoporeia captured off bottom increased over summer, peaking on 31 July. Pontoporeia were captured in day tows on 26 September at the station 1, 40 foot (12.2m) contour (Figure 8). Nearly all Pont0poreia collected in night tows on this date were taken from stations 1 and 2 lakeward of the 10 foot (3.0m) contour. Fall densities of Pontoporeia had declined to approximate spring levels. Entrainment A precipitous decrease in Pontoporeia entrainment occurred on 15 May (Table 25). However, estimates of Pontoporeia in Lake Michigan were increasing (Table 24). Farfield densities at the impact stations were highest at the 40 foot (12.2m) contour. Entrainment estimates of Pontoporeia were extremely variable, occasionally exhibiting more than a ten-fold increase during summer sampling (Table 25). Significant increases were noted in late July and early August. The peak summer entrainment estimate of 607,474 occurred on 15 August (Table 25). Numbers of Pontoporeia decreased in fall entrainment collections (Table 25). Nearly all amphipods entrained in fall were juveniles. 70 Table 25. Total number of Pontoporeia hoyi estimated to be entrained into the Ludington Pumped Storage Reservoir during 1979. Sample Number Estimated Number Date Entrained Entrained for Interval Interval 4/16/79 118,772 1,727,608 4/12 - 4/24 5/1/79 61,708 783,082 4/25 - 5/8 5/15/79 0 0 5/9 - 5/22 5/29/79 25,359 314,304 5/23 - 6/5 6/12/79 37,159 610,168 6/6 - 6/20 6/28/79 39,253 448,906 6/21 - 7/4 7/10/79 0 O 7/5 - 7/21 7/31/79 426,815 9,652,215 7/22 - 8/8 8/15/79 607,474 9,827,585 8/9 - 8/21 8/27/79 0 0 8/22 - 9/11 9/25/79 263,878 5,995,881 9/12 - 10/12 10/30/79 153,522 5,441,306 10/13 - 11/12 34,807,055 4/12 - 11/12 71 Reservoir Low numbers of Pontoporeia hoyi were taken in reservoir tows during both day and night sampling. The only occurrence of Pontoporeia in day tows was on 28 May at station 9 (Table 26). The initial appearance of Pontoporeia in night tow samples also occurred on 28 May. Peak pelagic density was noted on 10 July at station 7 (Table 26). Most Pontoporeia were collected in night tows made at station 9 with densities ranging from 0 - 26 individuals per 1000m3 of water recorded. Extrainment Pontoporeia were collected in extrainment samples only on 15 August during summer sampling (Table 27). Pontoporeia were collected during extrainment sampling on four of six dates during summer (Table 4). No Pontoporeia sp. were captured in extrainment tows made on 26 September (Table 27). Oligochaetes Farfield The only collections of oligochaetes during farfield day tows in spring were made on 29 May at station 1 (Figure 9). The majority of naidid oligochaetes taken at night were also captured on this date with most collected south of the power plant (stations 1 and 2). Most naidid oligochaetes were collected at station 2. At stations where oligochaetes were taken there appeared to be a trend of lakeward increase in spring (Table 28). Peak pelagic abundance of naidid oligochaetes was evident during 72 Table 26. Mean densities of Pontoporeia hoyi (#/1000m3) in samples from the Ludington Pumped Storage Reservoir during 1979. Total Reservoir Station 7 Station 9 Density Date Day Night Day Night Day Night 5/10/79 0 -- 0 -- 0 -- 5/15/79 0 0 0 --- 0 0 5/28/79 0 0 17 18 8 9 6/12/79 0 0 --- 0 0 0 6/28/79 0 0 0 26 0 13 7/10/79 0 57 0 6 0 31 7/31/79 0 0 0 3 0 1 8/15/79 0 0 0 17 0 8 8/27/79 0 13 0 5 0 9 9/25/79 0 0 0 24 0 12 73 Table 27. Total number of Pontoporeia hoyi estimated to be released from the Ludington Pumped Storage Reservoir during 1979. Number Estimated Number Date Extrained Moved for Interval Interval 5/1/79 0 0 4/25 - 5/8 5/15/79 0 0 5/9 - 5/22 5/29/79 0 0 5/23 - 6/5 6/12/79 0 0 6/6 - 6/20 6/28/79 0 0 6/21 - 7/4 7/10/79 0 0 7/5 - 7/21 8/1/79 0 0 7/22 - 8/8 8/15/79 624,090 7,587,741 8/9 - 8/21 8/27/79 0 0 8/22 - 9/11 9/26/79 10,400 217,401 9/12 - 10/12 7,805,142 4/25 - 10/12 74 .mna. ea ucmam Nosom omeONm moaesm couwawosa m :u Home announce an meowumum ucwummwwo um Aoooaowmzv mmummzoowfiao mo Anacoo.\.ozv muammon .m muawfim 75 ~ v ZOESM :.1 __ n 20.735 . ZO_N<..m :___ N ZO...(..m m... _uoueN Noouaoo casuaa poaaoueou on cu moumaauoo mouoonoomwao outflow mo muonsbz .mN OHAMH 77 summer farfield tows (Figure 9). Highest daylight density (241/1000m3) was recorded on 15 August at station 1, 30 foot (9.1m) contour. Oligo- chaetes were collected at all stations on this date. MOSt naidids captured in day tows were taken at station 1. Peak night densities of naidid oligochaetes occurred at the 5 foot (1.5m) contour during summer sampling with the mode (290/1000m3) occurring on 31 July. Lowest pelagic densities during night sampling occurred lakeward of the 10 foot (3.0m) contour at stations 3 and 4. Estimated abundance within the hypothetical rectangle was highest at the 40 foot (12.2m) contour (Table 28). Naidid oligochaetes were collected in day tows made at the 40 foot (12.2m) contour at stations 1 and 4 in fall (Figure 9). Peak day collection density was noted at the 5 foot (1.5m) contour at station 2. Peak density (989/1000m3) for the sampling year occurred in night collections made at the 5 foot (1.5m) contour. Greatest numbers of naidids were estimated at the 40 foot (12.2m) contour as a consequence of volume increases with depth (Table 28). Entrainment Oligochaetes were collected on two occasions during Spring entrain- ment sampling (Table 2). All oligochaetes entrained during summer sampling were members of the family Naididae (Nais sp. and Stylaria sp.). Oligochaete entrainment values ranged from O - 1,461,605 during summer (Table 2). No oligochaetes were captured in fall tow series during entrain- ment sampling. 78 Reservoir The first collection of naidid oligochaetes during day tows occurred on 28 May at station 9 (Table 29). Peak day pelagic density occurred on this date. Collection of naidids was quite sporadic with densities ranging from O - 21 organisms per 1000m3. Initial appearance of naidid oligochaetes in night tow samples was delayed until 15 August (Table 29). Peak night pelagic density was recorded on this date at station 9. Definitive conclusions on naidid distribution patterns were obscured by their limited occurrence in samples. General trends indicated that the majority of organisms were concentrated at station 7. Extrainment Highest release during spring sampling occurred on 29 May for oligochaetes (Table 30). These were identified as mostly Egi§.§p;_with some Stylaria sp. also present. The entrainment value for naidid oligochaetes averaged roughly 62 of the corresponding summer extrainment estimate. Substantial numbers of oligochaetes were released from the reservoir in late August (Table 30). Minor Taxa Farfield Ephemeroptera were collected infrequently in spring farfield night tows. Members of the families Siphlonuridae (Isonychia sp.) and Hepta- geniidae (Heptagenia sp.) were collected at all stations. Heaviest con- centrations appeared to be shoreward of the 30 foot (9.1m) contour (Table 31) for figptagenia sp., with most distributed at stations 1 and 79 Table 29. Mean densities of naidid oligochaetes (#IlOOOma) in samples from the Ludington Pumped Storage Reservoir during 1979. Total Reservoir Station 7 Station 9 Density Date Day, Night Day Night Day, Night 5/10/79 0 -- O --- 0 -- 5/15/79 0 O O --- 0 0 5/28/79 0 O 21 0 10 0 6/12/79 0 O --- 0 0 0 6/28/79 0 O 0 0 0 0 7/10/79 8 0 O 0 4 0 7/31/79 0 0 10 0 5 0 8/15/79 0 1,617 10 3,977 5 2,797 8/27/79 0 1,640 4 15 2 827 9/25/79 0 8 O 0 O 4 80 Table 30. Total number of naidid oligochaetes estimated to be released from the Ludington Pumped Storage Reservoir during 1979. Number Estimated Number Date Extrained Moved for Interval Interval 5/1/79 27,702 56,159 4/25 - 5/8 5/15/79 0 0 5/9 - 5/22 5/29/79 76,287 844,978 5/23 - 6/5 6/12/79 40,526 1,403,452 6/6 - 6/20 6/28/79 0 0 6/21 — 7/4 7/10/79 0 0 7/5 - 7/21 8/1/79 89,235 1,564,485 7/22 - 8/8 8/15/79 1,377,006 16,741,760 8/9 - 8/21 8/27/79 738,914 11,934,293 8/22 - 9/11 9/26/79 0 0 I 9/12 - 10/12 32,545,127 4/25 - 10/12 81 N...A...A N.N...N.. N...N...N NAA.N.. N.N.... .o..NmN .muoe .m....N NNA.NAN o o o .A... aN\AN\A .NA..N .NA..N o o o o aN\NN\. o o o o o o mN\A.\. 0.... o o o 0 cm... AN\.A\N . o o o o o AN\..\N o o o o o o AN\.N\. m...A.. o ..N.... o o ..m.. AN\N.\. .AN.NNm A...AA .AA..o. NAN.N. N...A Aqm.. AN\AN\A .o...No.. mmN...N.. NA..ANA.. ....mA. No...o. ANA...N AN\A.\A Noo.NN. o .oo.... o...A. AAN.. .A..~ AN\.\A m.m..m. o A...A.. ....NN o o ANN..\. .muoN c. on oN o. A a... sumac uaousoo .mnmfi ca unmam nosom omeOum monabm doumcwvsa onu Home oawsmuomu Hmoauonuoahn ax~.m x ¢.N a fig mam>uouca uaousou casuws mocwmusoo on cu mounaaumo Annouaouoaonamv movwacowwuamm mo muogasz .fim manna 82 2. Siphlonuridae were distributed at all stations on 1 May but were captured mainly at the 40 foot (12.2m) contour (stations 2 and 3) during the 15 and 29 May sample series (Table 32). Members of the families Perlodidae (ISOperla sp.) and Chaoboridae (Chaoborus sp.) were also collected sporadically during spring farfield tows as well as members of the order Hirudinea. Mayflies (EphemeroPtera) were collected occasionally during far- field tows made in summer. Members of the families Baetidae (Baetis sp.), Heptageniidae (flgptagenia sp.),and Siphlonuridae (Isonychia sp.) appeared in samples. Heptagenia sp. and Isonychia sp. were captured primarily at the 5 (1.5m) and 10 foot (3.0m) contours (Tables 31 and 32), while Baetis sp. were taken in deeper water. Chaoboridae, Ceratopogonidae (Diptera), Tubificidae (Oligochaeta), HydrOpsychidae (Trichoptera) and Hirudinea also were identified from tows made at night in the farfield area during summer. Hydropsychid caddisflies (Trichoptera), heptageniid mayflies (Ephemeroptera) and tubificid oligochaetes were also collected in the fall sample series in low numbers. Entrainment Chaoboridae (Chaoborus sp.), Perlodidae (Isoperla sp.), Hepta- geniidae (Heptagenia sp:,Stenonema sp.), Isopoda (Asellus sp.) and Ephemeridae were infrequently collected during the course of entrainment sampling in 1979 (Table 2). Their occurrence in reservoir and extrain- ment samples was similarly low. 83 N.A.ANN.A A.....A.. .m..N.... .A..Ao. m.m.N. .m...A .m... o o o o o o AN\AN\A NN...A o N.N..A o o o.... AN\NN\. N.N.N o o o o NAN.N aN\A.\. o o o o o o AN\.A\N o o o o o o aN\o.\N .AN.. o o o o .AN.. mN\.N\. m¢A.oAA ....oAA o o o .om... AN\N.\. ....A. «OA.AN o o A...A o .N\AN\A .qm...N ..m...N .o o o o mN\A.\A .AN.o.A.N ..A..AN.. .Nm.o.o.. .A..Ao. .AN... N...A aN\.\A o o o o o o AN\..\. .m... o. oA oN o. A m... suaoa usouaoo .23 5 ”Em... 530.. owmuoum .595... .8352... on”. you: oawcwuoou 30305093 5.5m x e.~ m 5 mam>umuaa unouaoo canuw3 mocfimuaoo on ou voumafiuoo Amuwuaouoamnnmv movauaaoa59fim mo muonssz .Nm manna DISCUSSION Mysis relicta Mysis relicta was the most common taxa distributed in the farfield area and entrained into the pumped storage reservoir (Tables 2 and 5). .HZEEE were the third most abundant organism returned to Lake Michigan (Table 4). Mysis relicta is primarily a benthic organism abundant in deep waters (>25m), but has been recorded in the shallows in spring and fall (Carpenter et al. 1974, Holmquist 1959). Beeton (1960) documented the vertical migrations undertaken by mysids in the Great Lakes. Reynolds and Degraeve (1972) recorded migration across depth contours. These migrations are a year-round phenomenon in deep lakes in the temperate zone (Morgan and Beeton 1978, Brownell 1970). .Mzgi§_serve as a fish food source at various stages, times or seasons during their existence (Michigan State University, Ludington Research Laboratory, unpublished data). ‘ EZEEE were taken in spring farfield day tows only on 29 May (Figure 3). Their low incidence was either a consequence of gear avoidance during day tows or a negative phototactic response. Beeton (1960) recorded initiation of Mysis descent when surface light intensity increased from 10.3 to 10-2 ft-candle during night sampling, indicating a marked sensitivity to intense light. In laboratory experiments,at least two visual pigments were isolated, one with an absorption peak at 84 85 515mu and another with a peak at or below 395mu (Beeton 1959). He con- cluded that sensitivity at 515mu was important in orientation, and sensitivity to violet light (395mu) possibly initiated negative photo- taxis. Degraeve and Reynolds (1975) found mysids to be more tolerant of intense light at low temperatures. Peak My§i§_densities at the 12.2m contour during Spring night tows occurred on 16 April at stations 2 and 3 (Figure 3). High densities were also recorded on this date at the 6.1m and 9.1m contours. Table 6 lists the entrainment estimate on this date, indicating that organisms distrib- uted lakeward of the 6.1m contour at these stations (2 and 3) were more susceptible to pumping currents created by the plant. Most water entrained from Lake MiChigan on the pumping mode is drawn from depths lakeward of 6m. Table 5 lists the estimated number of mysids contained within the hypothetical rectangle. Approximately 1% of the mysids estimated to be distributed in this volume (188,499,840m3) were entrained on 16 April. Maturity data indicated that entrained Mysis were adult (11 - 15mm) and subadult (6 - 10mm) instars. Gravid females were evident in tow collections. Current data collected in 1978 revealed highest velocities between the 6 and 14m contours near the power plant (Liston et al. 1979). Peak spring entrainment occurred on 29 May when approximately 182 of the My§i§_within the hypothetical rectangle were entrained (Table 5). (Mysis densities at the 6.1m and 9.1m contours at stations 2 and 3 were roughly equivalent to values recorded on 16 April. However, maturity data for mysids indicated that most individuals collected on 29 May were juveniles (<6mm). It appears that juvenile [Mygig_are less able to actively avoid entrainment. Juvenile My§i§_move further and descend later than adults (Brownell 1970, Beeton 1960). 86 This behavioral characteristic may possibly increase both the degree and duration of exposure to pumping currents and subsequent entrainment. Lessened inshore abundance appeared to be the cause of the decline in adult (>11mm) mysids collected in farfield and entrainment tows as spring sampling progressed. Table 5 lists EQEEE distribution at depths in Lake Michigan. Those individuals taken shoreward of the 6.1m contour through 15 May were late instars (<9mm). Peak spring farfield concentration occurred on 1 May. Feeding on the spring bloom of Melosira was recorded by Bowers and Grossnickle (1978). Melosira is abundant during this period in the study area (Liston and Tack 1973). Reservoir maturity data indicated most mysids taken were adults concentrated at densities above spring farfield values (Table 7, Figure 3). The higher reservoir densities for this length category indicate prolonged residence after initial entrainment of Mysis. Extended residence seems likely since entrainment values were higher than extrain- ment values over corresponding intervals during spring (Table 4). Definitive conclusions are obscured by data gaps in reservoir and extrainment samples in early spring. The incidence 0f.!12$§ in day tows during summer sampling increased but still remained significantly lower than night sample densities (Figure 3). The day-night catch disparity was either a consequence of vertical distribution or gear avoidance. Most mysids captured in day tows were taken at the 12.2m contour as a consequence of negative phototactic response. Juveniles dominated day collections. Tattersall and Tattersall (1951) concluded that immature Mysis relicta were less sensitive to light. Holmquist (1959) encountered Mysis concentrated several meters off-bottom in 8." 20m of water on a cloudy, rainy 87 afternoon. Variations in Mysis distribution during day tows appeared to be a consequence of stage of maturity of the individuals collected, secondarily influenced by varying meteorological conditions. .§Z§£§ farfield night densities increased during summer sampling as mysids moved inshore on feeding forays (Figure 3). Major increases at inshore contours (<9m) were a function of escalated numbers of juveniles captured in collections. Release of young was recorded in May by Beeton (1960) in Lakes Michigan and Huron. Adult mysids were predominantly distributed at farfield stations at depths greater than 6m during summer sampling. Vertical migrations of adults was arrested at approximately 10m in offshore waters (Beeton 1960). This was attributed to active concentration near the metalimnion. Nocturnal Mysis migrations into a metalimnetic chlorophyll a maximum.were observed by Bowers and Grossnickle (1978). Grossnickle (1979) found these migrations to be a response to food availability. MeWilliams (1970) recorded remains of Cladocera sp., diaptomid copepods, Melosira sp., Tabellaria sp. and Stephanodiscus sp. in mysid digestive tracts. Smaller frustules of the same diatoms were found in juveniles. Lasenby_and Langford (1973) found mysids to be carnivorous at night and omnivorous by day, feeding on Daphnia sp., Kellicottia sp., algae and detritus. Juveniles <6mm fed exclusively on algae and detritus. Melosira sp. was recorded in high concentrations in April (35 - 40/ml) and late June (60 - 80/ml) in Lake Michigan (Liston and Tack 1973). Tabellaria fenestrata and Stephanodiscus also were noted at peak concentrations during the period late April - early May. Both Melosira sp. and Stephanodiscus sp. are euplanktonic, while Tabellaria fenestrata may be tycoplanktonic. These diatoms would be distributed in the water column. Water temperatures 88 during this period are normally 5 - 9C in the inshore zone. ‘Mysig_density increases on 31 July at the 6.1m and 9.1m contours at stations 1 and 2, and the 3.0m contour at station 2 were the consequence of an upwelling. Bottom temperature was found to have a greater influence than depth on shoreward distribution of mysids (Reynolds and Degraeve 1972). Shoreward increases were also noted during upwellings, and Beeton (1960) noted increased densities near surface associated with upwellings. Hulbert (1957) found horizontal migrations to be affected by currents or active seeking of more favorable substrate. ‘Mzgig_maturity data indicated that both adults and subadults increased in inshore tows made on 31 July. Brooks and Torke (1977) described an algal layer situated near the metalimnion in summer. As previously stated, Bowers and Grossnickle (1978) recorded E1212 migration into this algae layer. Large quantities of Cladophora sp. were noted in collections made on 31 July at depths above the matalimr nion. Larkin (1948) found Mysis abundant among Cladophora sp. in shallow bays of Great Slave Lake. .EZEEE densities on 31 July were greatest at the 6.1 and 9.1m contours at stations 2 and 3 (Figure 3). Concomitant entrainment increases were again noted with farfield density increases at the 6.1 and 9.1m contours at stations 2 and 3 (Table 2, Figure 3). As pre- viously stated, most water moved through the plant is drawn from the 6m contour lakeward (Liston et al. 1979). The accompanying entrainment increase (1396/1000m3; peak value for the collection term) was caused by either active migration to shallower depths at the impact stations (2 and 3) or passive transport in upwelling currents. Higthygig densities were also noted at the 6.1 and 9.1m contours at stations 2 89 and 3 on 10 July, resulting in high numbers entrained (Figure 3, Table 5). Bowers and Grossnickle (1978) recorded peak metalimnetic chlorophyll a concentrations (9mg/m3) to occur at inshore stations. Reynolds and Degraeve (1972) presented evidence for mysid migration across depth contours at their shallow stations (9 - 55m). .EZEEE possibly are con- centrated on the edge of the nearshore zone and move inshore when food is abundant, making them susceptible to entrainment. Mysis, particularly adult instars, avoided the nearshore zone after the formation of a well defined metalimnion in early August as indicated by declining farfield and entrainment densities (Tables 2 and 5). Beeton (1960) felt high epilimnetic temperatures repressed mysid migra- tion. McNaught and Hasler (1966) found approximately 752 of their population did not migrate across the metalimnion. Brownell (1970) found immatures (<6mm) to migrate approximately 10m past the thermocline at a change of 2c/m. Degraeve and Reynolds (1975) indicated that Mysis relicta can tolerate temperatures up to 13C, but mortality increased rapidly at temperatures above 13C. Lethal temperatures varied with exposure duration. Beeton (1960) recorded ascent rates ranging from 0.4m/min. to 0.8m/min. Using these ascent rates and the average range between hypolimmetic and surface water temperature for Lake Michigan near Ludington of 1.18C to 1.570 during stratification, Mygi§_would be exposed to temperature rate increases ranging from .47c/min. to 1.97c/ min. during migrations. The upper limit is approximately twice the rate of increase used by Degraeve and Reynolds (1975) which yielded a TL50 (median tolerance limit) of 20.40, with marked mortality increase above 13C. Water temperature in the inshore waters of Lake Michigan normally ranges from 13 - 18C during stratification periods (Liston and Tack 1973). 90 Gravid females again appeared in farfield night collections in late July through early August. Females in the 16 - 20mm size class were collected during this period and in spring (16 April - 29 May). This agrees well with frequency peaks of instar V females recorded by Morgan and Beeton (1978) in Lake Michigan. They noted that these females com? posed a significant portion of the breeding population. The brood produced in late summer would be their second released (Morgan and Beeton 1978). Their absence nearshore during early summer was probably related to avoidance of elevated temperatures during the early part of embryo development. Berrill (1969) found heartbeat to be initiated in nauplii approximately three months old by temperature elevations from 3 to 150. He also found periodic temperature elevation to stimulate the integration of activity rhythms (yolk movement, abdominal contrac- tion, appendage fluttering). Tattersall and Tattersall (1951) docu- mented that reproduction will not occur at temperatures above 70. Gravid females possibly avoid the warm epilimnion in the early summer during the initial stages of nauplii development. Their movement into the epilimnion at night during the final stages of nauplii development initiating integration of organ systems. Brownell's (1970) findings support this hypothesis. Increased farfield and entrainment representation by juveniles (<6mm) was a consequence of their proportional increase after release from the females' marsupia. Harder (1968) noted that young mysids showed no reaction to thermal stratification. Frequency peaks of <6mm individuals were noted in early April, and in late July through early August in sample tows in all areas. Morgan and Beeton (1978) found major peaks in the proportions of first instar individuals in tows made 91 in March, July and November. McWilliams (1970) found four periods of release of juveniles in southern Lake Michigan. Instar peaks and corresponding size frequency data collected corresponded well with observed size frequency peaks in my collections in 1979. ‘Mz§i§_distribution patterns in the reservoir during summer sampling . underscored their documented avoidance of intense light and currents. (Degraeve and Reynolds 1975, Gregg and Bergerson 1980). ‘My§i§_densi- ties in day tows were below farfield day densities at comparable depths with the exception of station 9 on 29 May (Figure 3, Table 7). Samples taken at station 9 on 29 May contained clay indicating that the net had bumped bottom. Those tows were not reflective of pelagic abundance. Mysids collected at station 9 evidenced higher pelagic concentra- tions during day tows (Table 7). .Mygig are possibly still disoriented from exposure to the pressure regime encountered during turbine passage. This, coupled with the tendency for "freshly" entrained water to be directed into the northern end of the reservoir resulting in the creation of severe currents possibly interfering with downward migration, may serve to keep the organisms suspended. Upward migration followed pressure increases in work done by Rice (1961). Light intensity varia- tions didn't change the pressure response. Night densities in the reservoir were either comparable or higher than farfield night densities at equivalent depths throughout the collection term. These data indicate extended residence after initial entrainment. Station 7 densities were higher than station 9 Mysis densities during night tows (Table 7). Current velocities are lower in the south end of the reservoir (Lawson 1977). Current directions and velocities have not been recorded in the reservoir because of assumed 92 variability produced by combinations of units Operating. However, the homeothermous condition of the reservoir (Liston et al. 1976) and daily cycling of water with Lake Michigan create severe currents. .Mygig exhibit avoidance of current (Gregg and Bergerson 1980, Janssen 1978). Robertson et al. (1968) have directly observed actively swimming H1212 to maintain position in currents of 5 - 10cm/sec indicating possible avoidance of extrainment currents by.§l§$§' Survival in reservoir current regimes may also be possible but feeding would probably be limited or nonexistent in the reservoir. Bowers and Grossnickle (1978) were unable to initiate feeding in mysid cultures when current was introduced. Gregg and Bergerson (1980) found My§i§_mortality on ex- posure to current to increase significantly over the 8-day experimental period. They also suggested that the adverse effect of turbulence increased with temperature elevation. Most (80 - 902) of the mysids captured in summer reservoir tows were juveniles (<11mm). Carpenter et al. (1974) documented Mysis increases in the shallows in fall. The incidence of mature (>11mm) mysids in farfield night tows increased in fall collections. Most were taken lakeward of the 6.1m contour at all stations (Figure 3). Entrainment estimates remained high for fall as a consequence of the high volumes of water withdrawn from Lake Michigan (Table 6). Fall reservoir densities were comparable to early summer estimates (Table 7). Extrainment of mysids was low over the ten sample series in 1979 (Table 8). Overall, approximately 5.2% of entrained Mg§i§_were esti- mated to be released by the plant (Table 4). Entrainment-extrainment comparisons analyzed seasonally, revealed highest percentage return of entrained mysids occurred in spring (14.3%). Percentage return values 93 decreased from summer (5.1%) through fall (.41). Organisms pumped into the reservoir may remain there for some time during periods of the year. Another important consideration was the frequency of entrainment- extrainment sampling in 1979. Low sampling frequency increased the possibility that large entrainment-extrainment peaks may have been missed, thus confusing the relationship between entrainment and extrain- ment. Greater numbers of Mysis were captured when samples were taken during periods of generation in darkness. Many organisms may leave the ‘reservoir during the short periods when the plant generates after dark. Estimation 0f.!l§$§ release was calculated using a weighting factor to compensate for the hypothesized increase in densities during periods when the plant generated in darkness. A ratio of density after sunset to total density was determined on three dates when night samples were taken. R B-T' A a density after sunset (6) T - "total" density R - density ratio The ratios were averaged over the dates available. Through algebraic manipulation it can be shown then that: . R x B 1 - R A B = density before sunset (7) This relation was used to calculate A on dates when only before sunset densities (B) were determined. Conversely, B could be estimated for dates when only A was available. The density estimates thus obtained were multiplied by the appropriate total volume for the sample period to produce estimated numbers extrained. In some cases the revised estimates were lower than the initial estimates, due mainly to changes 94 in partitioning of the water volume moved. A total of 75,484,303 Mysis were estimated to be released to Lake Michigan resulting in an estimate of 5.8% of the entrained mysids to be returned to the lake. Therefore, it would appear likely that a current related mortality factor is in operation in the reservoir. If.§l§l§ are entrained while concentrated inshore during upwellings and then avoid extrainment currents as data indicate, prolonged residence time in the reservoir would expose them to elevated water temperatures from volumes moved during subsequent pumping periods. Loss of Mysis following initial entrainment may also be a function of intolerance to high water temperature (Degraeve and Reynolds 1975). Survivorship of Mysis relicta cycled through the pumped storage power plant was extremely variable (Tables 33 and 34). Few mysids were captured both at the jetties and the control station during mortality sampling in 1979 and 1980. Sampling was geared primarily toward deter- mination of ambient and plant induced ichthyoplankton mortalities. Nets towed in an oblique fashion would possibly have been more effective in capturing mysids. However, captured organisms would be subjected to additional abrasion along the net surface attendant with towing in this manner, increasing sampling induced mortality. Samples taken on pumping and generating modes in 1979 indicated substantial survivorship independent of water temperature. Brownell (1970) noted that immature My§i§_were not markedly affected by water temperature elevation. It is important to note that, with the excep- tion of the 9 May samples all Mysis captured in tows were immatures (<11mm). Survivorship was 1002 for the 9 May trial based on 3 individ- uals captured. Few Mysis were captured at the plant site during 95 Table 33. Survivorship of Mysis cycled through the Ludington Pumped Storage Reservoir in 1979. - Water Generate-Pump Control Date Temperature Alive Dead Alive Dead 5/9/79 7.8 3 0 0 0 100% Survivorship -- 5/24/79 9.0 0 0 0 3 - Survivorship 0% 6/5/79 12.0 12 2 0 0 86% Survivorship -- 6/27/79 11.2 30 0 7 0 100% Survivorship 100% 7/5/79 8.0 2 0 -- -- 100% Survivorship -- 8/6/79 15.2 35 3 2 ' 1 92% Survivorship 67% 8/28/79 17.0 50 0 0 0 100% Survivorship -- Totals 132 5 9 4 Total Survivorship 96% 69% 96 Table 34. Survivorship of Mysis cycled through the Ludington Pumped Storage Reservoir in 1980. Water Generate-Pump, Control Date Temperature Alive Dead Alive Dead 4/30/80 7.8 0 0 20 0 -- Survivorship 100% 5/12/80 9.0 0 0 1 0 - Survivorship 100% 5/27/80 12.0 1 3 0 0 25% Survivorship -- 6/11/80 11.2 2 1 1 0 67% Survivorship 100% 6/26/80 8.0 0 0 0 0 - Survivorship -- 7/29/80 15.2 0 0 0 0 -- Survivorship -- 8/11/80 17.0 0 0 0 0 -- Survivorship - Totals 3 4 22 0 Total Survivorship 43% 100% 97 mortality sampling in 1980. This was a consequence of sampling during daylight generating periods when mysid release rate was lowest. As stated previously, plant impacts were based on the quantity of viable organisms returned to Lake Michigan in 1980. The low total survivorship at the plant evidenced in 1980 reflected the reservoir currentdwater temperature mortality factor. High survivorship in 1979 samples was a consequence of pooling samples taken on the generating and pumping modes since pumping mode samples contributed most to the total number of organisms captured. Sampling in 1978 also revealed high survivorship upon initial entrainment of mysids into the pumped storage reservoir (Liston et al. 1979). Mortality assessment as a consequence of plant activity for 1979 revealed substantial estimated loss 0f.!lfii§° Calculated loss to Lake Michigan was 1,240,756,775 individuals for 1979. This results in an estimate of approximately 97% 0f.!Z§$§ unaccounted for after initial entrainment into the Ludington Pumped Storage Power Plant Reservoir. Effects of losses of this magnitude to the entire Lake Michigan system are inestimable. lyygig provide a substantial portion of the forage base, eaten by smelt, Osmerus mordax (Hale 1960), adult and juvenile bloaters, Coregonus hoyi (Yanusz 1979, Wells and Beeton 1963), juvenile lake trout, Salvelinus namaycush (Dryer et al. 1969), burbot, Lota lota (Bailey 1972) and fourhorn sculpins, Myoxocephalus,guadricornis (Wells 1980). Actual losses of My§i§_at the Ludington Plant may be lower simply as a consequence of underestimation of organism release from the plant. Extensive sampling to determine Mysis extrainment during periods of plant generation after darkness was not possible due to manpower limita- tions in 1979. Large numbers of mysids are suspected to leave the plant, 98 particularly during periods of generation late in the week when reservoir volume is reduced. Since one of the variables in the model used to estimate losses is the number of organisms returned (extrained) to Lake Michigan, underestimation of organism release results in an over esti- mate of plant induced loss. Thus, the 1979 loss estimate is probably high but can be used as an upper-bound. Definitive conclusions with respect to Mysis relicta loss rate require the implementation of extensive field sampling to provide sufficient extrainment data to confidently address mortality determination. Chironomidae Chironomid larvae were the third most abundant organism distributed limnetically near the pumped storage plant (Table 9), and were second and first in dominance in entrainment and extrainment collections, respectively (Table 4). The family Chironomidae is subdivided into seven subfamilies, Orthocladiinae, Chironominae, Diamesinae, Tanypodinae, Podonominae, ‘Telmatogotoninae, and Aphroteniinae (Merritt and Cummins 1978). Ortho- cladiinae occur in both lentic and lotic habitats and are primarily distributed in colder regions. Tanypodinae and Chironominae are prin- cipally distributed in lentic habitats with higher numbers occurring in warm regions. The Diamesinae are, as a group, rheophilic, occupying well aerated habitats (Pennak 1978, Oliver 1971). Chironomid dominance in spring farfield day tows at the 3.0 and 6.1m contours appeared to be caused by either active seeking of pre- ferred substrates or passive transport in alongshore currents. Spring day densities were substantially below those recorded in night tows. 99 Chironomid limnetic activity peaked about 0200h based on entrainment sampling. Larvae developing in unfavorable substrates also actively migrate into the water column (Hilsenoff 1967). Turbulence created by storm activity may also cause pelagic migration in Chironomidae (MMndie 1957). The 1978 current data indicated peak velocities at 6 and 14m. Highest densities occurred at contours subjected to extrained water from the plant (Figure 4). Planktonic existence of first instar chironomids is a common dispersal mechanism (Davies 1974, Oliver 1971). Peak farfield night densities in spring occurred in May at the 1.5 and 3.0m contours at stations 4 and 2, respectively. Tanypodinae were first noted in samples and were probably associated with increased oligochaete densities occurring on 29 May. Greatest overall densities were recorded at station 2. Farfield density increases at the 6.1 and 9.1m.contours at stations 2 and 3 were followed by entrainment increases in May (Table 9, Figure 4, Table 11). Extrainment peaks coincided with entrainment peaks in spring. Highest day densities were recorded in the north end of the reservoir, thus maximizing exposure to extrainment currents. The dominance of Tanypus sp., Procladius sp., Chironomus spg, and Glyptotendipes sp. at shallow contours (1.5 and 3.0m) was probably related to food, temperature and substrate preference. Teter (1960) found Chironomus sp,, Crytochironomus sp. and Glyptotendipes to be restricted to shallow depths. Barton and Hynes (1978a) recorded Chironomus fluviatilis-grp. in gravel beds nearshore in spring in Lake Erie. McLachlan (1976) found Glyptotendipes paripes to prefer coarse substrates. Chironomus lugubris was found associated only with sub- strate types rich in micro-organisms (MCLachlan and Dickenson 1977). Hilsenoff (1966) found Chironomus plumosus to feed mostly on diatoms in 100 Lake Winnebago. Tanypus sp. and Procladius sp. are free living predators and are associated with food availability which would be high due to allochthonous inputs creating a rich faunal assemblage. Eukieferriella ‘22; and Monodiamesa sp. abundance at 10.0 and 12.2m was probably related to food and substrate preferences (Davies 1975, Dendy 1973), Thut 1969). Diamesinae were associated with rock or cobble substrates. A predom- inance of third and fourth instars was revealed in spring collections of Eukieferriella sp. The larvae overwinter as second and third instars and emerge in early summer the following year (Liston et al. 1978). Chironomid pupae were collected during night at station 1 on 15 and 29 May at the 1.5 and 3.0m contours. Tanypodinae larvae and Chironominae pupae were also present in reservoir collections. Peak emergence was recorded in late May (personal observation) and identified pupae were Chironominae, Diamesinae and Orthocladiinae. Hilsenoff (1966) linked Chironomus plumosus emergence to diatom density peaks in Lake Winnebago. This feeding stimulus was necessary for Q;_plumosus to pupate and emerge. Highest day pelagic chironomid densities in summer occurred at station 2 shoreward of the 10.0m contour, probably as a consequence of wind generated current disruption of the sediments. Again day densi- ties were substantially below those recorded at night. Hilsenoff (1966) found water currents to be an important determiner of g; plumosus distribution. Davies (1978) found chironomdd larvae leave the sub- strate repeatedly in response to increases in water current speed at the sediment-water interface. Oliver (1971) suggests that chironomid movement in lakes may be density dependent, initiated by crowding, re- duced resources, and/or unfavorable environment. These stimuli also may 101 initiate migration into the water column near the power plant. Entrainment peaks in summer occurred in early June and late August and were associated with density increases lakeward of the 6.1m contour at stations 2 and 3. Most entrained water is drawn lakeward of the 6.0m contour (Liston et a1. 1979). Current data revealed highest velocities at 6 and 14m during plant operation modes. Plant generated currents may serve to increase migration from the substrate into the water column, thus increasing the susceptibility of larvae to entrainment currents. Chironomid extrainment trends and composition generally mimicked entrainment during summer. The peak pelagic densities of chironomids during night tows in late July and August were partially a consequence of large numbers of third and fourth instar Chironomus sp, and Cryptochironomus sp. active in the water column. Late instar chironomid larvae commonly display premature pupal behavior (Davies 1974, Dugdale 1955). Peak pelagic activity culminated in emergence on 27 August. Similar pulses were noted in reservoir collections. Pupal densities were highest on this date at the 10 and 12.2m contours. Chironominae dominated pupal collections, but Tanypodinae and limited Diamesinae were also noted. Peak larval density occurred at the 1.5m contour at station 1 but overall densities were highest at stations 1 and 2. This may indicate either higher benthic density south of the plant or greater migratory activity displayed by larvae in this area. Possible differences in substrate particle size may also influence larval distribution (Cummins and Lauff 1969, McLachlan 1969, Marks and Henderson 1970). Duffy and Liston (1978) analyzing four years of benthic sampling in Lake Michigan found greater diversity evident in the benthic 102 community south of the plant, particularly at station 1. Chironomids and oligochaetes dominate the benthic community at stations 2 and 3, with chironomid benthic abundance greatest between 6 and 12m. The relative homogeneity of the substrate at station 1 compared to those encountered at the impact stations (stations 2 and 3; Table I‘IN_Duffy and Liston 1978) may account for the difference. Current data, collected in 1978 indicates plant generated currents are reduced at stations 2 and 3. However, the number of units operating, coupled with wind direction and ambient current conditions, can periodically subject benthos at these stations to current regimes above ambient levels during plant operation. Vertical migration exhibited by chironomids may be an avoidance response to this or other environmental disturbances (Davies 1978, Hilsenoff 1967, Bay et a1. 1966, Waters 1964, Mundie 1957). Most chironomids captured in fall day tows were taken at stations 1 and 4. Densities decreased lakeward with peak night density occurring at 2.0m on 26 September. Instar determination and pupal identification indicated that limited emergence of Orthocladiinae was occurring at this time. Mortality associated with turbine passage for chironomid larvae was determined in 1979. Survivorship for chironomids was in excess of 95% so mortality assessment was not attempted. Entrained chironomids were determined to colonize the reservoir (Lawson 1977). Reservoir tows in 1979 indicated a build-up of chironomid larvae in the southern half of the reservoir (Table 12). Most of these individuals were Chironomus sp. Lawson (1977) reported the rare occurrence of orthoclads in benthos samples in the southern end. Chironominae were found to dominate the southern third of the reservoir, possibly as a response to current and 103 food availability (Lawson 1977). The rheophilic species Monodiamesa sp. colonized the northern two-thirds of the reservoir. Major currents occur in this area and possibly, substrate and current regimes present in the reservoir may closely approximate those found in rivers. Day densities of pelagic chironomids were generally higher in the north end while night density peaks occurred in the southern portion of the reservoir (Table 12). This phenomenon was assumed to be associated with plant induced currents on the generating (day) and pumping (night) modes. Distribution and degree of exposure to plant generated currents appears to be a consequence of microenvironmental preference for chironomids. Dispersal of first instar larvae by active migration into the water column appears to be behavioral (Oliver 1971). Migration by older instar individuals is initiated in response to storm generated turbulence (Davies 1974, Mundie 1966); unfavorable substrate (Hilsenoff 1966); crowding (Paterson and Fernando 1971); and decreased dissolved oxygen concentration (Bay et al. 1966). The distribution of Chironomidae is assumed to be a result of the miCrodistribution patterns of current,substrate type and food. Wetzel (1975) states that most organic matter (75 - 99%) in lakes is decomposed in the water column before reaching bottom. In the inshore zone allo- chthonous production provides a rich substrate for both bacterial and detritivore activity. However, this material is not distributed uniformly on the substrate, creating a mosaic distribution pattern in the chironomid fauna. Variation in spatial distribution of chironomids may also be affected by some behavioral component of dispersion (Paterson and Fernando 1971). It is likely that the particulate organic matter pool in the nearshore area (particularly at stations 2 and 3) is 104 enhanced by plant activity and associated fish kills causing organic enrichment (Liston et al. 1981). Amphipoda Pontoporeia hoyi has been reported as the dominant benthic inverte- brate in the profundal zone of Lake Michigan (Marzolf 1965b, Teter 1960). Pontoporeia was the second most abundant organism estimated to be distributed in the farfield area within the hypothetical rectangle (Table 24), the fourth most abundant macroinvertebrate entrained and the sixth most abundant released (Table 4). Although Pontoporeia is not abundant in the nearshore area (<15m) of Lake Michigan (Duffy and Liston 1978), their large size magnifies their importance as a forage item. Pontoporeia has been observed in strata as shallow as 1.5m (Barton and Hynes 1978b, Wells 1968). Figure 8 indicates few PontOporeia nearshore in spring. Most Pontoporeia nearshore were subadult instars captured only during night tows. Barton and Hynes (1976b) recorded Pontoporeia as common on sand substrates at depths of roughly one meter. Nearly all of these indi- viduals were immature instars. Adult instars dominated farfield night collections on 16 April lakeward of the 6.1m contour. Marzolf (1965b) observed less than 8% of the total population to take part in diel migrations. Adult and subadult instars were the predominant migrants. The continual decline in Pontoporeia entrainment from the inception of farfield sampling through 15 May appeared to be a consequence of decreased density at the 6.1 and 9.1m contours at stations 2 and 3 (Figure 8). Pontoporeia entrainment increased again on 29 May as organism abundance increased at stations 2 and 3, increasing organism 105 exposure to plant entrainment currents (Figure 8). Pontoporeia abundance in the farfield area increased abruptly in late June as first instar individuals dominated collection at all depths. This coincides with the period of release observed previously in Lake Michigan (Liston et al. 1978, Duffy and Liston 1978, Mozely 1974). Fluctuation in amphipod populations was attributed to juvenile recruitment. High numbers of juveniles in samples in both 1978 and 1979 nearshore in tows support this conclusion. The majority of PontOporeia sampled at the shallow contours in early summer and after stratification in August were juveniles. Appar- ently juvenile instars are more tolerant of elevated water temperatures. Determination of 24 and 96 TLm (median tolerance limits) yielded values of 12C and 10.9C at an acclimation temperature of 6C (Rees 1972). These values indicated probable higher lethal temperatures. Pontoporeia may also migrate into the nearshore zone for a limited time, retreating to a colder deep water refugium. The marked increase in Pontoporeia entrainment on 31 July was a consequence of a massive increase in organism abundance at all contours in the farfield area (Table 24). Density increases at the 6.1 and 9.1m contours at stations 2 and 3 caused concomitant entrainment increases since these areas provide the majority of the source-water for entrain- ment. Approximately 14% of the total volume of water estimated to be contained within the hypothetical rectangle was pumped into the reservoir on this date. The peak summer entrainment value on 15 August was also related to Pontoporeia density at the 6.1, 9.1 and 12.2m contours at stations 2 and 3. Values remained at or above those recorded for 1 August while the total number of Pontoporeia within the rectangle 106 declined by approximately 50% due to density declines at stations 1 and 4 (Table 25, Figure 8, Table 24). Avoidance of rising temperature may Vhave initiated retreat to deeper water. No distinct reason is apparent for their paucity in farfield collections during this portion of the year. Release of Pontoporeia from the reservoir may have been under- estimated, as they are negatively phototactic (Marzolf 1965b). Reser- voir tow density data indicated low concentration of Pontoporeia in the water column with peak densities occurring in station 9 night tows. These organisms are possibly freshly entrained as most water is directed into the northern third of the reservoir (personal observation). Lawson (1977) and Olson (1974) recorded Pontoporeia among the reservoir benthos over the year. Their findings would suggest that they are more abundant than extrainment data indicate (Table 27). Pontoporeia abundance declined abruptly in fall (Table 24). Olson (1974) and Koehler (1975) noted increased abundance of Pontoporeia in the reservoir in October in benthos samples and drift net sets, respectively. Lawson (1977) recorded reduced numbers in fall. Mozely (1974) noted variations in fall Pontoporeia collections and attributed them to time of release of young. Station 1 and 2 displayed higher pelagic densities of Pontoporeia than 3 and 4 in fall. This phenomenon was also noted during summer collections and is probably related to substrate differences. Station 1 and 2 are dominated by sand substrate providing ideal colonization habitat for Pontoporeia. Barton and Hynes (1976) noted Pontoporeia's preference for sand, recording population densities of up to 30/m2 in nearshore areas. These densities are far below values recorded for deeper areas (Mezely and Alley 1973) but are 107 probably related to non-uniformity of the habitat and/or bacterial content and distribution in the sediment (Marzolf 1965a, Paterson and Fernando 1971). Gammarus fasciatus and Gammarus pseudolimnaeus combined were the fourth most abundant macroinvertebrate group estimated to be contained within the hypothetical rectangle (Tables 16 and 17). They ranked fifth in abundance in entrainment and extrainment, respectively (Table 4). Gammarus spp. have been found to primarily inhabit the breakwall and jetties. Colonization has been attributed to current, substrate and food (Duffy and Liston 1978). These species represented 46% of entrain- 5 ment and 68% of extrainment estimates for amphipods. Entrained Gammarus app. were drawn from the jetty area as evidenced by low farfield densi- ties (Figures 6 and 7). Adult §E_pseudolimnaeus tolerated maximum current speed of 54.86cm/sec, a value slightly below average current speeds recorded between the jetties (Rees 1972). Plant generated currents probably influence Gammarus spp. farfield distribution. High- est Gammarus_p§eudolimnaeus densities occurred at the 1.5m contour at station 1, generally. Barton and Hynes (1976) recorded them as abundant on boulder substrates. Rees (1972) documented their preference for gravel to cobble substrates. Gammarus fasciatus were recorded infrequently in collections in the farfield area in spring. May sampling in the littoral zone in Lake Erie produced similar results (Barton and Hynes 1976). Olson (1974) recorded Q; fasciatus on rock basket samplers from the jetties. Most pelagically active g; pseudolimnaeus occurred at the deep contours (6.1 and 9.1m) at station 2 during day tows in summer. Night 108 tows indicated peak activity at the 1.5 and 3.0m contours. Organisms sampled during daylight may be diapersed by plant generated currents or are simply active at these depths, migration to the shallows occurring _ at night. Barton and Hynes (1978a) felt that Gammarus app. move directly in and out of the wave zone during calm weather. Shallow contour collections of Q; pseudolimnaeus and Q; fasciatus revealed these individuals to be juvenile instars. Their absence in the water column during the day may also simply be a behavorial response to avoid predation. Entrainment samples during summer also were dominated by juvenile §§_fasciatus and §E_pseudolimnaeus. Gammarus app. entrainment increases were associated with release of young in summer. The low incidence of §E_fasciatus in farfield collections was probably a consequence of their close affinity for Cladophora sp. covered substrates (Barton and Hynes 1978b, Bocsor and Judd 1972). Barton and Hynes (1978b) also found §;_fasciatus in the gravel trough immediately below the swash step in summer. ‘Q; fasciatus remained in the shallows through fall, retreating to a deep water refugium with the onset of severe weather (Barton and Hynes 1976). The paucity of Gammarus app. in reservoir samples indicated low numbers of these organisms distributed pelagically in the reservoir, since Olson (1974) and Lawson (1977) recorded them as common members of the benthos during their studies. In fact, percent release of Gammarus pseudolimnaeus exceeded 100% of the entrainment estimate on several dates during summer, indicating biomass produced in the reservoir. Total release of Gammarus spp. was higher than the value recorded for Ponto- poreia but subordinate to Gammarus app. entrainment (Table 4). 109 All amphipods entrained into the reservoir on dates in 1979 and 1980 were combined for survivorship determination. Pont0poreia comprised roughly 54% of entrained amphipods with the remaining 46% being Gammarus spp. Results are admittedly scant, but entrainment survivorship appears high (Tables 35 and 36). Exposure of Gammarus app. to simulated turbine passage pressure regimes at the Cornwall Pumped Storage Power Plant pro- duced no significant mortality (Beck et al. 1975). Enright (1961) found a sensitivity threshold during rapid pressure increase between .007 - .015 atm. The vertical migrations of Pontoporeia hoyi and attendant hydrostatic pressure variation have been documented (Wells 1968, Marzolf 1965b). Survivorship determined for amphipods was 86% at the plant and 100% at the control stations, yielding generating mortality (Mg) and control mortality (Me) values of .14 and 0, respectively. Mortality due to mechanical effects at the Zion Generating Station was estimated at 10% a value slightly below that calculated at the Ludington Plant (Nalco 1976). The value determined for entrainment (NTe) was 64,024,719 with extrainment (NTx) estimated at 24,035,724 during the sample year at the Ludington Pumped Storage Power Plant. Calculated loss employing equation 5 (see Mortality Methods) yielded an estimate of 43,353,996 for the sample period. Again, as with Mysis this is probably an upper- bound estimate due to the low values for NTx Oligochaeta The naidid oligochaetes Stylaria SE; and Nais sp. were not common in the farfield area until late spring. Stylaria dominated collections throughout the year. Highest densities occurred nearshore during Table 35. 110 Survivorship of amphipods cycled through the Ludington Pumped Storage Reservoir in 1979. Water Generate-Pump Control Date Temperature Alive Dead Alive Dead 5/9/79 7.8 4 0 0 0 100% Survivorship -- 5/24/79 9.0 1 0 0 0 100% Survivorship -- 6/5/79 11.2 8 4 1 0 67% Survivorship 100% 7/5/79 8.0 1 1 O 0 50% Survivorship -- 8/6/79 15.2 I 15 1 1 0 94% Survivorship 100% 8/28/79 17.0 7 1 O 0 88% Survivorship -- Totals 36 7 2 0 Total Survivorship 84% 100% 111 Table 36. Survivorship of amphipods cycled through the Ludington Pumped Storage Reservoir in 1980. Water Generate-Pump Control Date Temperature Alive Dead Alive Dead 4/30/80 7.8 0 0 15 0 - Survivorship 100% 5/12/80 9.0 2 0 0 0 100% Survivorship -- 5/27/80 12.0 0 O 0 0 -- Survivorship -- 6/11/80 11.2 2 0 0 0 -- Survivorship -- 6/26/80 8.0 3 1 1 0 75% Survivorship 100% 7/29/80 15.2 0 0 '0 O -- Survivorship -- 8/11/80 17.0 0 0 0 O -- Survivorship -- Totals 7 1 16 0 Total Survivorship 88% 100% 112 farfield day and night sampling throughout the sample term (Figure 9). Increase lakeward for naidids was a consequence of increased volume with depth. Stimpson et al. (1975) found naidids distributed in greatest numbers at 3 and 6m. Abundance decreased lakeward with none noted at the 18m contour. Hiltunen (1967) collected Naididae from Lake Michigan between the 5.5 - 18.5m contours. He noted that some naidids are active swimmers, stating that others could be transported in alongshore currents. Wiley and Mozely (1978) also recorded Naididae active in the water column. Low densities at stations 3 and 4 were possibly related to naidids preference of sand substrates (Stimpson et al. 1975). Naidid densities remained high through early fall at the 1.5m contour (Figure 9). Estimates of Naididae entrainment were roughly equivalent to extrainment values (Table 4). Reservoir pelagic occurrence (Table 29) generally coincided with release peaks (Table 30). Olson (1974) did not record Stylaria sp. or §§i§_in reservoir benthos collections. Lawson (1977) grouped the naidids under "rare species" in his collections. They may remain active in the water column until release generation periods. The increased numbers in late summer and fall collections corresponds with peak maturity and reproduction for Naididae (Hiltunen 1967). He collected mature Stylaria sp. in September samples. Naididae feed primarily on algae and detritus (Pennak 1978). Minor Taxa Infrequently collected taxa were grouped under this heading. Their low abundance did not warrant mortality determinations. Collected taxa 113 include Ephemeroptera, Plecoptera, Trichoptera, ISOpOda and Diptera. Members of the Ephemeroptera collected during sampling included the families Siphlonuridae, Isonychia sp.; Heptageniidae, Heptagenia sp., Stenonema sp.; Ephemeridae, Ephemera sp. and Baetidae, Baetis sp. Isonychia sp. and Baetis sp. are active swimmers (Shapas 1976). Some of the Baetidae employ migration into the water column as a dispersal mechanism (Corkum 1978). Siphlonurids were relatively common in spring at the deeper contours at stations 2 and 3. Barton and Hynes (1978a) recorded Baetis sp. as common on cobble and boulder substrates. Hepta- genia sp. and Stenonema sp. also were noted on cobble size substrates. SCUBA observations at stations 1 and 2 revealed heptageniids to be distributed in crevices on rocks and boulders. Stenonema sp. was identified only in spring farfield and entrainment samples. Olson (1974) found Stenonema sp. throughout spring and summer on rock basket samplers at the jetties. He recorded one individual in collections in the reservoir in June. One Ephemera sp. was collected during entrain- ment sampling. Plecoptera collected consisted of the Perlodidae genus IsoEerla‘gp; Isoperla SE; was collected in spring farfield and entrainment samples. One Isoperla sp. was captured on boulders at the 6.1m contour at station 2 while diving. This individual was captured with a partially engulfed Diamesinae larva. Fahy (1972) found ISOperla sp. to be carnivorous with roughly 5% of its gut contents consisting of algae and detritus at productive habitats. Hydropsyche spp. were captured occasionally in all areas during sampling in 1979. They were taken infrequently in farfield tows in summer and fall. Benthic densities at station 2 were estimated at 114 20 - 30/m2 during dives in August. TrichOptera were observed to con- struct cases on the undersides of and crevices between rocks. Barton and Hynes (1978a) noted that net structure and alignment were highly variant hypothesizing that the erratic current pattern in the nearshore zone may restrict less flexible species. Isopoda, identified as Asellus spg, were collected in all areas. Asellus sp. were common inhabitants of the jetties and breakwall and the rock scour pad within the reservoir (Olson 1974, Lawson 1977). They are probably accidental inhabitants of the water column. Dipterans of the families Chaoboridae and Ceratopogonidae were infrequently collected during sampling. Chaoborus sp. was identified in farfield night tows in spring and summer. Two Ceratopogonids were captured in summer farfield night.tows. Kajak et al. (1978) noted migration to deeper contours as maturation advanced. Hirudinea were seldom collected in farfield and reservoir tows. Condition of captured specimens did not allow identification. Barton and Hynes (1978b) collected leaches occasionally in .Sm of water. SUMMARY During 1979 it was attempted to estimate day/night abundance, distribution, entrainment and release rates, and survivorship of macro- invertebrate drift organisms near the Ludington Pumped Storage Power Plant. Macroinvertebrates were sampled biweekly at four stations and five contours (1.5, 3.0, 6.1, 9.1, 12.2m) in Lake Michigan, one site between the jetties and two stations in the upper reservoir from 17 April to 30 October 1979. 'One meter plankton nets (351p) towed in an oblique fashion were employed to determine farfield abundance, reservoir densities and entrainment/extrainment rates, while mortality sampling employed use of a two meter plankton net in a vertical haul. Impacts of power plant operation were compared to estimated organism abundance in a hypothetical rectangle (2.4 x 9.7km) in Lake Michigan surrounding the plant, for assessment. A total of 1045 collections were made on 19 dates in 1979 (739 in farfield day/night collections; 89 for entrainment; 74 reservoir; 68 extrainment; and 75 mortality samples). Farfield collections were dominated by Mysis relicta, four chironomid subfamilies, two genera of amphipods (Pontoporeia and Gammarus) and naidid oligochaetes. Entrain- ment/extrainment and reservoir collections were composed of the same taxa though their order of abundance was not identical. Mysis relicta was the most abundant organism collected in Lake Michigan on all dates, though abundance continually declined after 115 116 31 July. Densities of Mysis ranged from 0 - 7871/1000m3 exhibiting a definite lakeward increase. Lower numbers of Mysis were collected at the control sites (stations 1 and 4), and appeared to be caused by plant Operation. Chironomids were collected on all sample dates. Chironominae were captured on all dates, though peak concentrations were noted in farfield samples from June through August. Orthocladiinae exhibited a bimodal peak in late May and July through August. Orthocladiinae occurrence was low in early spring and fall collections. Diamesinae larvae were noted from June through August, and nearly absent in fall. The predaceous Tanypodinae were the least abundant of the chironomids, virtually absent in samples until late May - early June and again in late August. Total concentration of Chironomidae ranged from 0 - 5990/1000m3. Larvae were more abundant at stations 1 and 2 with peak abundance recorded at station 2. Amphipods were collected on all sample dates, though differences between Pontoporeia and Gammarus were substantial. Pont0poreia were collected on all dates with greatest abundance occurring in late June through August. Densities of PontOporeia ranged from 0 - 4O6/1000m3. A positive relationship between density and increasing depth was observed at all stations. Gammarus pseudolimnaeus were at all stations and depths but were concentrated in the shallows. First appearance in abundance was in early June with densities ranging from 0 - 1192/ 1000m3 recorded. These organisms appeared to be associated with cobble and gravel substrates. Gammarus fasciatus were the least abundant amphipod in pelagic collections. They displayed densities ranging from 0 - 30/1000ma in collections. Gammarus fasciatus were associated with 117 Cladophora sp. covered substrates. Spatially, Gammarus spp. appeared to be more abundant at stations south of the power plant. The naidid oligochaetes Stylaria sp. and N§i§_§p;_were recorded in tow collections in the farfield area beginning in early June, with abundance ranging markedly. Pelagic occurrence for these organisms was a combination of active entry of the water column and passive dispersal in strong water movements. Mysis relicta were collected in reservoir tows from the inception of sampling. Densities ranged from 0 - 9O8/1000ma during sampling. Peak day densities occurred in the north end (station 9) of the reservoir while night density modes were noted in the south end (station 7). Highest pelagic densities were recorded in the south end of the reservoir. This phenomenon was attributed to current avoidance associated with plant operational mode. Densities of chironomid larvae fluctuated from 0 - 3047/1000m3, after initial collection in the reservoir in.May. Station 7 exhibited highest night densities while peak day densities occurred at station 9. Highest densities occurred in station 7 during night tows. Chironomid pupae were captured sporadically, with initial appearance occurring on 28 May. Two density pulses were indicated from reservoir collections, one in early June, and another in late July to early August. Pupal densities ranged from 0 - 836/10001113 during sampling. Low numbers of both Pontoporeia and Gammarus app. were captured during day and night sampling in 1979. Pontoporeia hoyi and Gammarus pseudolimnaeus were collected initially on 28 May, while Gammarus fasciatus was first captured on 15 May. Gammarus spp. pelagic activity was low in comparison with concentrations recorded in previous benthic 118 investigations. Limited incidence of Pontoporeia in the reservoir was indicated by low tow densities and previous benthic sampling. Collection of naidid oligochaetes was quite sporadic. Densities in tows ranged from 0 - 3977/1000m3 in day/night samples. Distribution patterns in the reservoir indicated the majority of organisms to be concentrated at station 7. All the major groups of macroinvertebrates collected in farfield samples were observed in entrainment/extrainment samples. Mysis relicta were again the most abundant organism entrained and second in extrain- ment samples. Peak Mysis entrainment occurred in late June through July and a total of roughly 1.3 billion were entrained over the sample term. Sixty-seven million Mygig_were extrained. Chironomidae were the second most abundant organism entrained and the most abundant in extrainment samples. Midge larvae were composed of the same subfamilies collected in farfield samples. A total of 188 million chironomids were entrained and 195 million were released. Both species of amphipods were taken in entrainment collections while §;_pseudolimnaeus was the most abundant gammarid. More Gammarus spp. were released from the reservoir than Pontoporeia. A total of nearly 7 million Pontoporeia were released while Gammarus spp. extrainment was 16 million. Entrainment for EEEEST poreia and Gammarus spp. was roughly 35 and 29 million, respectively. Loss estimates of My§i§_indicated that approximately 97% of the initially entrained organisms were unaccounted for (1,240,756,775 individuals). Survivorship of My§i§_was generally high. Loss estimates were affected principally by low extrainment values and should be used as an upper-bound. 119 Survivorship of amphipods (Pontoporeia and Gammarus combined) was 86%. Estimated loss was set at 43,253,996 for amphipods over the sample period. This value is also affected by the low extrainment estimate. LITERATURE CITED LITERATURE CITED Armstrong, J. W. 1973. Age, growth and food habits of the round white- fish, Prosopium gylindraceum (Pallas), in central Lake MUchigan, M.S. Thesis, Mich. State Univ., Dept. of Fish. and Wildl. 76 pp. Bailey, M. M. 1972. Age, growth, reproduction and food of the burbot, Lota lota (Linnaeus), in southwestern Lake Superior, Trans. Amer. Fish. Soc., 101(4):667-674. Barton, D. R. and H. B. N. Hynes. 1978a. Wave-zone macrobenthos of the exposed Canadian shores of the St. Lawrence Great Lakes. J. Great Lakes Res., March 1978 4(1):27-45. and H. B. N. Hynes. 1978b. Seasonal variations in densities of macrobenthic populations in the wave-zone of north-central Lake Erie. J. Great Lakes Res., March 1978, 4(1):50-56. and H. B. N. Hynes. 1976. The distribution of Amphipoda and IsOpoda on the exposed shores of the Great Lakes. J. Great Lakes Res., Dec. 1976, 2(2):207-214. Bay, E. C., A. E. Ingram and L. D. Anderson. 1966. Physical factors influencing chironomid infestation of water-spreading basins. Ann. Ent. Soc. Amer. 59(4):714—717. Beck, A. P., G. V. Poje and W. T. Waller. 1975. A laboratory study on the effects of the exposure of some entrainable Hudson River biota to hydrostatic pressure regimes calculated for the proposed Cornwall Pumped Storage Plant. Pages 167-204 l2 S. B. Saila, ed. Fisheries and energy production: A symposium. D. C. Heath and 00., Toronto, Can. Beeton, A. M. 1960. The vertical migration of Mysis relicta in Lakes Huron and Michigan. J. Fish. Res. Bd. Can., 17(4):517-539. . 1959. Photoreception in the Opossum shrimp, Mysis relicta Loven. Biol. Bull., 116:204-216. Berrill, Michael. 1969. The embryonic behavior of the mysid shrimp, Mysis relicta. Can. J. 2001. 47:1217—1221. 120 121 Bocsor, J. G. and Judd, J. H. 1972. Effect of paper plant pollution and subsequent abatement on a littoral macroinvertebrate community in Lake Ontario: preliminary survey. .Im_Proc. 15th Conf. Great Lakes Res., Internat. Assoc. Great Lakes Res., pp. 21-34. Bowers, J. A. and N. E. Grossnickle. 1978. The herbivorous habits of Mysis relicta in Lake Michigan. Limnol. Oceanogr. 23(4):767-776. Brazo, D. C. and C. R. Liston. 1979. A study of the effects of installing and Operating a large pumped storage project on the shores of Lake Michigan, near Ludington, Michigan. The effects of five years of operation of the Ludington Pumped Storage Power Plant on the fishery resources of Lake Michigan (1972- 1977). 1977 Annual Rep., Ludington Proj. Vol. II, No. 1, Fisheries Research. Submitted to Consumers Power Co. Mich. State Univ., Dept. Fish. and Wildl. Ludington Res. Lab. 406 pp. . 1973. Fecundity, food habits and certain allometric features of the yellow perch (Perca flavescens Mitchill) before Operation of a pumped storage plant on Lake Michigan. M.S. Thesis, Mich. State Univ. 75 pp. Brooks, A. S. and B. G. Torke. 1977. Vertical and seasonal distribution of chlorophyll a in Lake Michigan. J. Fish. Res. Bd. Can. 34:2280-2287. Brownell, W. 1970. Studies on the ecology of Mysis relicta in Cayuga Lake. M.S. Thesis, Cornell Univ., Ithaca, NY. 67 pp. Cannon, T. C., S. M. Jinks, L. R. King and G. R. Laver. 1978. Survival of entrained ichthyOplankton and macroinvertebrates at Hudson River power plants. .23 71-91 L. D. Jensen, Ed. Fourth National Workshop on entrainment and impingement. E. A. Communications, Melville, NY. Carpenter, G. P., E. L. Mansey, and N. H. F. Watson. 1974. Abundance and life history of Mysis relicta in the St. Lawrence Great Lakes. J. Fish. Res. Bd. Can. 31:319-325. Carter, 8. R. 1977. Macroinvertebrate entrainment study at Fort Calhoun station. Pages 155-169 Im_Fourth National WorkshOp on entrainment and impingement. L. D. Jensen, Ed. Corkum, L. 1978. The influence of density and behavioral type on the active entry of two mayfly species (Ephemeroptera) into the water column. Can. J. 2001. 56:1201-1206. Cummins, K. W. and G. H. Lauff. 1969. The influence of substrate particle size on the microdistribution of stream macrobenthos. Hydrobiologia. 34.145-181. 122 Davies, B. R. 1974. The planktonic activity of larval Chironomidae in Loch Leven, Kinross. Proc. R. Soc. Edinb., 74:275-283. . 1978. Studies on the effect of wind induced water currents and temperature on the planktonic activity of larval Chironomidae in Loch Leven, Kinross. Davies, I. J. 1975. Selective feeding in some arctic Chironomidae. Verh. Int. Verrin. Limnol. 19:3149-3154. Degraeve, G. M. and J. Reynolds. 1975. Feeding behavior and temperature and light tolerance of Mysis relicta in the laboratory. Trans. Am. FiSho SOC. 104(2):394-3970 Dendy, J. S. 1973. Predation on chironomid eggs and larvae by Nanocladius alternatherae Dendy and Subletie (Diptera: Chironomidae, Orthocladiinae). Ent. News 84:91-95. Dryer, W. R., L. F. Erkkila and C. L. Tetzloff. 1965. Food of lake trout in Lake Superior. Trans. Amer. Fish. Soc. 94(2):169—176. Duffy, W. G. and C. R. Liston. 1978. An analysis of the percentage composition and abundance of benthic macroinvertebrates in Lake Michigan adjacent to the Ludington Pumped Storage Plant, 1972- 1976. Mich. State Univ., Dept. Fish. and Wildl. 1976 Ann. Rep. to Consumers Power Co., Limnol. Res. (Vol. II, No. 1). 97 pp. Dugdale, R. C. 1955. Studies in the ecology of the benthic diptera of Lake Mendota. Ph.D. Thesis, Univ. Wisconsin, Madison. Enright, J. T. 1961. Pressure sensitivity of an amphipod. Science 133:758-760. Fahy, E. 1972. The feeding behavior of some common lotic insects in two streams of different detrital content. J. Zool. Lond. 167:337-350. Ginn, T. C., G. V. Poje and J. M. O'Connor. 1978. Survival of planktonic organisms following passage through a simulated power plant condenser tube. .Ig_91-103, L. D. Jensen, Ed. Fourth National Workshop on entrainment and impingement. E. A. Communications, Melville, NY. Gregg, R. E. and E. Bergerson. 1980. ,Mysis relicta: Effects of turbidity and turbulence on short-term survival. Trans. Am. Grossnickle, N. E. 1979. Nocturnal feeding patterns of Mysis relicta in Lake Michigan, based on gut content fluorescence. Limnol. Oceanogr. 24:777-780. 123 Hale, J. 1960. Some aspects of the life history of the smelt (Osmerus mordax) in western Lake Superior, p. 25-41,'Im_Charles R. Burrows and Arnold B. Erickson, (Eds.) Minnesota Fish Game Investigation,Fdsh.Series No. 2, Minnesota Dept. Conserv. Harder, W. 1968. Reactions of plankton organisms to water stratifi- cation. Limnol. Oceanogr., 13:156-168. Hauer, F. R. 1975. Comparison of preoperational and operational abundance, age, length-weight relationships, and food habits of yellow perch, Perca flavescens (Mitchill), in Lake Michigan and the Ludington Pumped Storage Reservoir. M.S. Thesis, Mich. St. Univ. 75 pp. Hilsenoff, W. L. 1975. Aquatic insects of Wisconsin: with generic keys and notes on biology, ecology and distribution. Tech. Bull. No. 89, Dept. Nat. Res., Madison, Wis. 53 pp. . 1967. Ecology and population dynamics of Chironomus plumosus in Lake Winnebago, Wisconsin. Ann. Ent. Soc. Amer. 60(6):1183-1194. Hiltunen, J. K. 1967. Some oligochaetes from Lake Michigan. Trans. Amer. Micros. Soc. 86:433-454. Holmquist, C. 1959. Problems on marine glacial relicta on account of investigations on the genus Mysis. Lund. Berlinska Bokirychereit. 270 pp. Holsinger, J. R. 1976. The freshwater amphipods (Gammaridae) of North America. U.S. Env. Prot. Ag. Identification Manual No. 5. 89 pp. Hulbert, E. M. 1957. The distribution of Neomysis americana in the estuary of Delaware River. Limnol. Oceanogr. 2(1):1-11. Janssen, J. 1978. Feeding-behavior repertoire of the alewife, Alosa mpgeudoharengus, and the ciscoes Coregonus hoyi and g; artedii. J. Fish. Res. Bd. Can. 35:249-253. Jude, D. J. 1977. Entrainment of fish larvae and eggs on the Great Lakes, with special reference to the D. C. Cook Nuclear Plant, southeastern Lake Michigan. Third National Workshop of entrainment and impingement. 177-199. Kajak, Z., J. Rybak and B. Ranke-Rybieka. 1978. Fluctuations in numbers and changes in the distribution of Chaoborus flavicans (Meigen) (Diptera; Chaoboridae) in the eutrOphic Mikolajskie Lake and dystrophic Lake Floseic. Ekologia Polska (Ekol. Pol.) 26(2):259-270. Koehler, F. E. 1975. Analysis of the invertebrate and fish larval drift in the Ludington Pumped Storage Reservoir, 1975. Unpub- lished manuscript, Mich. State Univ. Ludington Res. Lab. 124 Larkin, P. H. 1948. Pontoporeia and Mysis in Athabaska, Great Bear and Great Slave Lakes. Bull. Fish. Rs. Bd. Can. 78:1-33. Lasenby, D. C. and R. R. Langford. 1973. Feeding and assimilation of Mysis relicta. Limnol. Oceanogr. 18:280-285. Lawson, D. L. 1977. The abundance and distribution of benthic macro— invertebrates in the Ludington Pumped Storage Reservoir. M.S. Thesis, Mich. State Univ., Dept. of Fish. and Wildl. 48 pp. Ligman, R. 1978. Food habits of burbot in Lake Michigan, near the Ludington Pumped Storage Power Plant. Unpublished manuscript, Mich. State Univ. Great Lakes Ludington Res. Lab. 25 pp. Liston, C. R., D. C. Brazo, R. P. O'Neal, J. Bohr, G. Peterson, and R. Ligman. 1981. Assessment of larval, juvenile, and adult fish entrainment losses at the Ludington Pumped Storage Power Plant on Lake Michigan. 1980 Annual Rep., Ludington Proj., Vol. 1, Submitted to Consumers Power Co., Mich. State Univ., Dept. of Fish. and Wildl. 276 pp. , D. Brazo, J. Bohr, R. Ligman, R. O'Neal, and G. Peterson. 1978. Preliminary report on progress of the 1978 aquatic research at the Ludington Pumped Storage Power Plant on Lake Michigan. 1978 Annl. Rep. Ludington Proj., Vol. I, NO. 1, Submitted to Consumers Power Co., Mich. State Univ., Dept. of Fish. and Wildl. 142 pp. , D. C. Brazo and P. I. Tack. 1976. A study of the effects Of installing and Operating a large pumped storage project on the shores of Lake Michigan near Ludington, Mich. 1974 Annl. Rep. to Consumers Power Co., Vol. II. Physical-chemical aspects. Dept. of Fish. and Wildl., Mich. State Univ. 65 pp. and P. I. Tack. 1973. A study of the effects of installing and Operating a large pumped storage project on the shores of Lake Michigan near Ludington, Michigan. Mich. State Univ., Dept. of Fish. and Wildl. 1973 Ann. Rep. to Consumers Power Co., Vol. I (Fisheries Research) 174 pp. Marks, R. J. and A. E. Henderson. 1970. An examination of the larval Chironomidae (Diptera: Nematocera) in Lennymore Bay, Lough Marzolf, G. R. 1965a. substrate relations of the burrowing amphipod Pontoporeia affinis in Lake Michigan. Ecology 46(5):579-592. . 1965b. Vertical migration of Pontoporeia affinis (Amphipoda) in Lake Michigan. Proc. 8th Conf. Great Lakes Res., Great Lakes Res. Div., Univ. Mich. pp. 133-140. 125 McLachlan, A. J. and C. H. Dickinson. 1977. Micro-organisms as a factor in the distribution of Chironomus lugubris Zetterstedt in a bog lake. Arch. Hydrobiol. 80(2):133-146. . 1976. Factors restricting the range of Glyptotendipes paripes Edwards (Diptera: Chironomidae) in a bog lake. . 1969. Substrate preferences and invasion behavior exhibited by larvae of Nilodorum brevibucca Freeman (Chironomidae) under experimental conditions. Hydrobiologia 33:237-249. McNaught, D. C. and A. D. Hasler. 1966. Photoenvironments of planktonic crustacea in Lake Michigan. Verh. Internat. Verein. MeWilliams, P. S. 1970. Seasonal changes in abundance and reproduction in the Opossum shrimp Mysis relicta Loven in Lake Michigan. M.S. Thesis, Univ. Sidney, 94 pp. Merritt, R. W. and K. W. Cummins. 1978. An introduction to the aquatic insects of North America. Kendall/Hunt Publishing Co., Dubuque, Iowa. 441 pp. Mikus, D. 1978. The food habits of the ninespine stickleback Pungitius pungitius (Linnaeus). Unpublished manuscript. Mich. State Univ. Great Lakes Ludington Res. Lab. 16 pp. Morgan, M. D. and A. M. Beeton. 1978. Life history and abundance of Mysis relicta in Lake Michigan. J. Fish. Res. Bd. Can. 35(9):1165-1170. Mozely, S. C. and W. P. Alley. 1973. Distribution of benthic invertebrates in the south end of Lake Michigan. Proc. 16th Conf. Great Lakes Res., Internat. Assoc. Great Lakes Res., pp 0 87-96 0 . 1974. Preoperational distribution of benthic macroinverte- brates in Lake Michigan near the Cook Nuclear Power Plant. pp. 5-138. ‘32 Seibel, E. and J. C. Ayers. 1974. The biolog- ical, chemical, and physical character of Lake Michigan in the vicinity of the Donald C. Cook Nuclear Power Plant. Univ. of Mich., Great Lakes Res. Div., Spec. Rep. No. 51, 475 pp. and L. C. Garcia. 1972. Benthic macrofauna in the coastal zone of southeastern Lake Michigan. Proc. 15th Conf. Great Lakes Res. 1972:102-116. Mundie, J. H. 1966. Sampling emerging insects and drifting materials in deep flowing water. Gewass. Abwass. 41/42:159-162. . 1957. The ecology of Chironomidae in storage reservoirs. Trans. Royal Ent. Soc. London 109(5):149-232. 126 Nalco Environmental Sciences. 1976. The effects of entrainment on Pontoporeia affinis in the vicinity of Zion and Waukegan gener- ating stations, March 1976. Rep. to Commonwealth Edison Co., Chicago, IL, by Nalco Environmental Sciences. Oliver, D. R. 1971. Life history of the Chironomidae. Ann. Rep. Ent. 16:211-230. Olson, G. R. 1974. The benthic macroinvertebrate populations in a new pumped storage reservoir and the adjacent coastal areas of central Lake Michigan. M.S. Thesis, Mich. State Uhiv. 220 pp. Paterson, C. G. and C. H. Fernando. 1971. Studies on the spatial heterogeneity of shallow water benthos with particular reference to the Chironomidae. Can. J. 2001. 49:1013-1019. Pennak, R. W. 1978. Freshwater invertebrates of the United States. John Wiley and Sons, Inc., New York. 803 pp. Rees, C. P. 1972. The distribution of the amphipod Gammarus pseudo- limnaeus Bousfield as influenced by oxygen concentration, substratum, and current velocity. Trans. Am. Microsc. Soc. 91:514-528. Reynolds, J. B. and G. M. Degraeve. 1972. Seasonal population character- istics of the opossum shrimp, Mysis relicta, in southeastern Lake Michigan, 1970-1971. Proc. 15th Conf. Great Lakes Res. (Internat. Assoc. Great Lakes Res.) pp. 117-131. Rice, A. L. 1961. The responses of certain mysids to changes in hydro- static pressure. J. Exp. Biol. 38:391-401. Robertson, A., C. F. Powers, and R. F. Anderson. 1968. Direct observations of Mysis relicta from a submarine. Limnol. Oceanogr. 13:700-702. and W. P. Alley. 1966. A comparative study of Lake Michigan macrobenthos. Limnol. Oceanogr. 11:576-583. Shapas, T. J. 1976. Feeding habits of Wisconsin's predominant lotic Plecoptera, Ephemeroptera and TrichOptera. Great Lakes Ent. Smith, W. E. 1972. Culture, reproduction and temperature tolerance of Pontoporeia affinis in the laboratory. Trans. Am. Fish. Soc. 101:253-256. Stimpson, K. S., J. R. Brice, M. T. Barbour, and P. Howe. 1975. Distribution and abundance of inshore oligochaetes in Lake Michigan. Trans. Amer. Micros. Soc., 94:384-394. Tattersall, W. M. and O. S. Tattersall. 1951. The British Mysidacea. London Roy. Soc. 460 pp. 127 Teter, H. E. 1960. The bottom fauna of Lake Huron. Trans. Am. Fish. Soc. 89:193-197. Thut, R. N. 1969. A study of the profundal bottom fauna of Lake Washington. Ecol. Menogr. 39:79-100. Tranter, O. J. and P. E. Smith. 1968 Filtration performance. 13. 27-57, Zooplankton Sampling. UNESCO Monogr. on Oceanogr. Methodol., Imprimeries Popularies, Geneva. Waters, T. F. 1964. Recolonization of denuded stream bottom areas by Wells, L. 1968. Daytime distribution of PontopOreia affinis off bottom in Lake Michigan. Limnol. Oceanogr. 13:703-705. Wetzel, R. G. 1975. Limnology. W. B. Saunders, Phila. 743 pp. Wiley, M. J. and S. C. Mozely. 1978. Pelagic occurrence of benthic animals near shore in Lake Michigan. J. Great Lakes Res. (Internat. Assoc. Great Lakes Res.) 4(2):201-205. Yanusz, R. 1979. Food habits Of juvenile and adult bloaters (Coregonus hoyi) near Ludington, Michigan. Unpublished manuscript. Mich. State Univ., Great Lakes Ludington Res. Lab. 23 pp.