v‘——v v 'v w.-. v‘vv- 'I-Iu-vv' '1 ' -—-w:u-vI-u. ‘o. -- .,..-’~so. 9‘0...“ ”Ho\o' o... ~O ‘0‘. v .-oo‘0‘l°_‘ DISTRIBUTION AND GROWTH . .. ... n ‘_ . . .— u. x . . _ _ . . o .1 o r ,. . . ¢ . . . .‘. < . . . . ‘ p . . . _ . . . . a . L . or :MMMURE SALVEUNUS NAMAYCUSH, HATCHERY - REARED LAKE TROUT. 0 IN LAKE MICHIGAN ........... 1.. .. .o.s ‘ .... ......?... ., . .... Thesis for the Degre off... . _ 2. ._ . I .41.. 3.23.: is c .. s e of M.» S. MICHIGAN STATE UNWERSlTY 3.. .o I... ls JOHN L. HESSE . 6 . ....:. . . .... i969 ......,..m..~r r. . . OI O‘O’lr ¢a.o‘ ’ O . o c. . .o 4 .< If... I??? .6 ...v..t .. . .3: o . . . .. .aa.’!?) 0 I; . r t . I I . '11....ullrffillo —. 1‘. :c.‘ . . no. ..r .. I, ‘ Ir. . .. Lif'v’fcll/r I. J-(waaJlr..¢‘. 2.. 3...; 3.51/35" I r . . O /. '. .. r’O‘ I 0. . . ' l M ,1 _ O_ A ,l D ’ I 'I O I ' O M? r '. _' o. ..(.l' r . O V ' “Ii-(,3; v . m mm m: nu mm 1mg; [fill 1!! fig!!! :11" I1 1:19am; f! L 3 1293 MAR I 3 1994 «PR I 7,1935 114 "' ABSTRACT DISTRIBUTION AND shown! or mm “mu-mun mu: rm, snmnms nmmusn, DI m HICHIGAN by John L. lease Lake trout Lnonitoring data from Michigan and Uisconsin waters of Lake Michigan were analyzed for the period of 1965 through 1967. O'lhe study is based upon 20,642 recoveries of juvenile hatchery- reared lake trout. The objectives were to determine the hathyletric distribution, the novuent or dispersal patterns, and the growth rate of the planted lake trout during their first three years at liberty. The greatest concentrations of juvenile lake trout were at 20-29 fatholss during the spring, sI-er, and fall seasons, and at 40-49 in the winter. Dispersal patterns away from planting sites are described for each of nine groups of narked lake trout. ‘i‘he aajority of the hatchery-reared trout remained within the general areas of release even after three years at liberty. However, soee extensive novuent did occur. Hove-ant away from the planting areas was generally . parallel to the shoreline. lo pattern of clocbsiae or counter- clockwise movement was evident. Extensive offshore novenent was linited to statistical district ill 3. The average lengths at capture for age groups I, II, and III ‘were 7.9, 11.3, and 15.7 inches, respectively. Back-calculated lengths at the first three annuli were 6.43, 10.34, and 14.34 inches. Compared to previous reports of lake trout growth in Lake'flichigan, the lake trout of the present study exhibited increased growth rates and were more robust. Lamprey scarring rates are presented and discussed. Gear selectivity of commercial gear types is reported. Reference is also made to the liadtations in using commercial fishery data for biological analyses. I‘!I.III I l l loll lrl|.l.!-| DISTRIBUTION AND’GIOHTK OP IHHATURE HATCIBBIBREARED LAKE TROUT, SALVELINUS'INHATCUSE, IN LAKE MICHIGAN By gi I“£‘ John L; nesse A THESIS Submitted to . Hflchigan State University in partial fulfillment of the requirements for the degree of HASTIR.0! SCIIICB Deparumant of Fisheries and'flildlife 1969 ACKNWLENMTS I wish to thank Hyrl Keller and Walter Crowe of the Michigan Department of Natural Resources for their cooperation in providing the data for this study and for their suggestions and guidance. I would also like to thank Mr. Russell Daly of the Wisconsin Department of Conservation, who willingly made data available from the Wisconsin lake trout monitoring program. iuy appreciation also is extended to Dr. Eugene Roelofs, chairman of my graduate con-ittee, and to connittee members, Br. Inward Johnson and Dr.‘noward Tanner. For financial assistance, I am indebted to the Bureau of Conmercial Fisheries, who gave support through a pre-doctoral fellowship over the period of September, 1965, through September, 1967. The computer analysis for this study was funded by the Agricultural Experiment Station, Michigan State University. Finally, my most sincere appreciation goes to ny wife, Harti, for her constant encouragement and patience. 11 TABLE OF comm IlTROMTION........... MEMSAIDHETIODS. . . . . . . Statistical Districts . . . . .. Release of Marked Lake Trout. . Collection of Data. . . . . . . Analysis of Data. . . . . . . . CEARSILECTIVITT......... sammc DISTRIBUTIOI . . . . . CIOCMICALHOVWTS. . . . . . "L9" Clip - Forth Shore . . . . "D" Clip - Reef and Island Area "RV" Clip - Grand Traverse Day. "RF" Clip - Multiple Locations. "D—RV" Clip - Ludington . . . . "IV" Clip - Kilwaukee Reef. . . "Ad" Clip - Door Peninsula and Kewaunee "LP" Clip - Door Peninsula and Kewaunee "D-LV" Clip '61?“ It, a e e e e e e 0 Discussion of nov-ents . . . . . . . . sun A: We 0 O O O O O O O O O 0 O O 1111 PAGE ##9 13 14 18 23 28 31 36 36 36 41 41 5 55 58 mes m-wnearnmnou..................69 mmnonsrsnumrs................. 75 smrmnomcrmmus.................. 80 immc1nn..................... 85 iv TABLE 1 . 2. LIST OF TABLES PAGE Marked lake trout in Lake Michigan (1965- 1967). O O O O O O O O O 0 O O O 0 O O O O O O O O 8 Length distributions of 20,551 lake trout caught in large mesh gill nets, small mesh gill nets, trawls, and trap and pound nets, 1966'1967eeeeeeeeeeeeeaeeeeeee15 The average number of lake trout caught per 1,000 feet of gill nets at different depths in Lake Michigan, during various seasons in 1966'1967eeeeeeeeeeeaeeeeeeeee 20 Location and number of recoveries in 1966 of hatchery-reared lake trout planted in various areas of Lake Michigan. Also year of plant- ingandmarkinguaed............... 26 Location and number of recoveries in 1967 of hatchery-reared lake trout planted in various areas of Lake Michigan. Also year of plant- ingandmarkingused............... 27 Percentage of recaptures according to statistical district for each of the fin- clips, 1966. Also total number of each fin-clip recovered . . . . . . . . . . . . . . . . 29 Percentage of recaptures according to statistical district for each of the fin- clips, 1967. Also total umber of each fin-cliprecovered...o..s...so.... 30 Length distribution of the age groups of marked lake trout recaptured in Lake Michigan, 1966 and 1967. . . . . . . . . . . . . . 56 Length distribution and area of capture for 402 lake trout fron which scale samples “r.0bt‘1n‘dsseeeeeeeeeeeeeeees 59 TABLE Ice 11. 12. 13. 13. 13. Total length at capture and lengths calculated by direct proportion from diameters of annuli on the scales of 'marked lake trout; age groups I, II, and 111. Year classes are combined; lengths are in inches. . . . . . . . . . . . Growth of lake trout for northern Lake Michigan, southern Lake Michigan, and areas combined. All values are from grand average increments based on calculated lengths at the and of the indicated years ofllfe................... Lengthdweight relationships for lake trout in the upper region, lower region, and Wisconsin waters of Lake Michigan; also for regions combined . . . . . . . . . . . . (a) Incidence of lamprey scarring on lake trout captured in upper Lake Michigan, 1966 and 1967. Data analyzed according to 1-1nCh length intchQIO. e e e e e e e e e e (b) Incidence of lamprey scarring on lake trout captured in lower Lake Michigan, 1966 and 1967. Data analyzed according to 1’1““ 1.11831 intew‘1.e e e e e e e e e e '9’ (c) Incidence of lamprey scarring on lake trout captured in Wisconsin waters of Lake Michigan, 1966 and 1967. Data analyzed according to l-inch length intervals . . . . vi PAGE 62 65 70 76 77 78 LIST OF FIGURES Statistical districts of Lake‘Michigan . . . . Percentage length distribution of lake trout caught in large mesh gill nets, small mesh gill nets, trawls, and impounhent “at O O O O O O O O O O O O O O O O O O 0 O 0 Areas of Lake Michigan from which samples "t. Obt‘i'ed, 1965-196? e e e a e e e e e e e Localities and number of returns of hatchery- reared lake trout having the ”LV" clip. Black circles are planting localities and open rectangles give the number of fish caught in each area; arrows indicate probable direction of movement . . . . . . . . Localities and number of returns of hatchery- - reared lake trout having the "D" clip. Ilack circles are planting localities and open rectangles give the number of fish caught in each area; arrows indicate probable direction of movement . . . . . . . . Localities and number of returns of hatchery- reared lake trout having the "IV" clip. Black circles are planting localities and open rectangles give the number of fish caught in each area; arrows indicate probable direction of movement . . . . . . . . Localities and number of returns of hatchery- reared lake trout having the "RP“ clip. Slack circles are planting localities and open rectangles give the number of fish caught in each area; arrows indicate probable direction of movement . . . . . . . . vii PAGE 17 25 33 35 38 nouns 8. 10. ll. 12. 13. 14. PAGE Localities and number of returns of hatchery- reared lake trout having the "D-EV" clip. Black circles are planting localities and open rectangles give the number of fish caught in each area; arrows indicate probable direction of movement . . . . . . . . . 43 Localities and number of returns of hatchery- reared lake trout having the "3V“ clip. Black circles are planting localities and open rectangles give the number of fish caught in each area; arrows indicate probable direction. of movement . . . . . . . . . 45 Localities and number of returns of hatchery- reared lake trout having the "Ad" clip. Black circles are planting localities and open rectangles give the number of fish caught in each area; arrows indicate probable direction of movement . . . . . . . . . 47 Localities and number of returns of hatchery- reared lake trout having the "LP” clip. Black circles are planting localities and open rectangles give the number of fish caught in each area; arrows indicate probable direction of movement . . . . . . . . . so Localities and number of returns of hatchery- reared lake trout having the "D-LV” clip. Black circles are planting localities and open rectangles give the number of fish caught in each area; arrows indicate probable direction of movement . . . . . . . . . 52 Calculated growth in length (from sunsha- tion of increments) for the present study, from Cable (1956), and from Vanoosten and Eschmeyer (1956) . . . . . . . . . . . . . . 67 Lengthdweight relations of lake trout of Lake Michigan. . . . . . . . . . . . . . . . . . 73 V111 IMTROMTION No studies have been conducted on the bathymetric distribu- tion, geographic distribution, or growth rate of juvenile lake trout, Salvelinus namaycush (Walbaum) , in Lake Michigan since their reintroduction in 1965. In light of drastic ecological changes which have occurred in the Great Lakes since the 1940's, new studies in these areas should be conducted and all previous available information be used as a yardstick of comparison. Van Oosten and Eschmeyer (1956) reported briefly on the bathymetric distribution of small lake trout collected during 1930-32. Smith and Van Costen (1940) conducted a study of geographic movement patterns, and studies by Cable (1956) , Van Oosten and Eschmeyer (1956) and Smith and Van Oosten (1940) provide documentation of the growth rates of juvenile lake trout in Lake Michigan prior to 1946. before the mid-1940‘s, the lake trout had long been a species of primary importance to the Lake Michigan fishery. Co-ercial catch records show a co-ercial take of 4 to 9 million pounds annually for the period of 1885 to 1945 (Duettner, 1965). Beginning in 1946, the stability of the fishery broke and production dropped catastrophically to 342,000 pounds by 1949 (Mile, Escheyer, and Lunger, 1951). Smith (1968) has attributed the decline to a combination of increased preda- tion by the sea lamprey, PetromLzon marinus, and to over-exploitation by the co-ercial fishery in the period just before the decline. Dy the mid-1950's, the population had reached near extinction (Feel-eyer, 1957). A similar crash had been already experienced in Lake Muron (Mile and Buettner, 1954) , and it was also evident that the stocks in Lake Superior were being severely reduced (Duettner, 1965) . As the lake trout stocks declined, _the con-ercial fishery was forced to switch its aphasia to chubs (Leucichthys s . . At the same time, the lamprey, with its supply of lake trout becoming limited, began praying heavily upon the larger species of chubs. Subsequent abrupt changes in the deepwater fish fauna of the Great Lakes resulted (Moffett, 1957; Smith, 1964, 1968) and culminated with the invasion and population explosion of a marine species, the alewife, _A_l_o_s:_ pseudoharengug. According to Smith, (1968) the Great Lakes had reached a state of biological instability by the mid-1960's that is almost unparalleled in the history of fishery science. Attempts to restore a useful fishery balance in the upper Great Lakes have been undertaken and the progress being made is encouraging. .A massive effort to control the sea lamprey using a toxicant that selectively destroys sea lamprey larvae in tributary streams has met with good success. A State and Federal restoration program of re-establishing predatory species in Lake Michigan was begun in 1965 with the planting of 1.3 million fin-clipped yearling lake trout. This has been increased to over 2 million annually and will be continued until natural reproductionis ra-established. In addition to the lake trout, plantings of steelhead trout. (SL193 gairdnerii) have been increased and coho (Oncogynchus kisutch) and chinook salmon (0ncorhynchus tshawytscha) have been introduced from the west coast. Following the reintroduction of lake trout in Lake Michigan, research is needed to learn something of their habits and to appraise the success .of the stocking program. A study of the feeding habits has been completed by Wright (1968). The objectives of the present study were to: 1) determine bathymetric distribution of planted lake trout; 2) gain knowledge of the movement or dispersal patterns during their first three years in the lake; and 3) estinte and compare the growth rates to those of juvenile lake trout in Lake Michigan previous to the population decline. MATERIALS AND METHOIB Statistical Districts For convenience and standardization in tabulation of fishery data, the Great Lakes and related waters have been subdivided into statistical districts (Smith, Duettner, and.Rile. 1961). Districts for Lake Michigan and Green Day are shown in Figure l. The author has conformed to these boundaries throughout this study. However, certain of the statistical districts have been grouped into general lake regions closely comparable to areas as described by Cable (1956). Three general regions'were formed and are defined as follows: Upper Lake Michigan . . . The area included within Statistical Districts as; 1 through us 5, inclusive. Lower Lake Michigan . . . The area included‘within Statistical Districts in 6 through II! S, inclusive. Wisconsin Waters. . . . . The entire area‘within Wisconsin state boundaries of Lake Michigan, In! 1 through WM 6, inclusive. Indiana and Illinois districts were not included in this study because data was not available from these waters. Release of Marked Lake Trout Planting of hatchery-reared lake trout into the Great Lakes has been conducted under the direction of the Great Lakes Fishery I ll I‘ll III I ’l r. Figure 1. Statistical districts of Lake Michigan .——-‘ «a a,!_ —_ —A_F .4 Mackinac Bridge HANI S'I‘I QUE ., mcu, W's. ETOSKY 1131:0151 1:33 f 4‘ WM-I G R 3:31! '1. BAY WM-4 / ' MM-6 gf‘ig Sable pts 1 M ICH [CA N PORT WHITE LAKE U WASHINGTON,- WM?’ l ‘ MM-7 MILWAUKEE _. \ -e---- DISTRICT BOUNDARY “““““““ 1 :1 HOLLAND -—-—-- INTERSTATE BOUNDARY VIM-6 ‘— vns ___ \ Ill -7 I mm '“- I , BENTON I HARBOR T1 CHICAGO :. w . it. N1 ___.. mi IND. INQ Comission. Pertinent data on the marking and release of the young lake trout are shown in Table 1 for the years of 1965, 1966, and 1967. The number of lake trout released during these three years totaled 5,415,108. Marking was accomplished by removal of fins. A study by Shatter (1951) has indicated that this method does not seriously affect the survival or growth of lake trout. Mo clips were repeated in consecutive years and, in most cases, plantings of individual clips were restricted to localized areas of the lake. Collection of Data The data for this study were collected through the efforts of the Michigan and Wisconsin Conservation Departments and loaned to the author for analysis. Data analyzed were for the two-year period from January 1, 1966 through December 31, 1967. The majority of the lake trout recovery information came from the co-aercial fishery as voluntary reports to the Conservation Departments, or from either dock or onboard inspections by Department Personnel of co—ercial fish catches. Each licensed fisherman has" been required to submit to the Department of Conservation a weekly report of incidental catches of lake trout in his gear, since season closure, October 1, 1965. Although the fishermen were allowed to keep legal sired lake trout which died in the nets, all live or sublegal (<17.0 inches) lake trout were to be returned to the water. a 22 name .oa A>mv nmmm mmnsmzanz onnma m.mm 0mm.aom .o .H mash meme mamuocm> zoom m 2.2 mend mama esmemH cam mmmm ma o.Hm ooo.moa .Hanm maze «woe Amy Hammom v 22 man meme A>mv mmue>mue cameo ummz ma 0.0m oom.ooa .m .N no: name Hmeocm> ucmnm meme .ma .uemm .ea .mH .mgn m 22 emacnnsmz mfiiea e.mH Ham.nmm .ofl .ma mash wean = meme .m .e .unmm gm emdm m :2 um>enesm manna o.mH cam.mam .ma .oe mesh Soon = mean .OH .0 .pamm .ma .HH .mse A>qv m :2 muommsoem manna n.¢a emm.oam .NH ease Some Hanucm> pawn m 22 noon manna .MUOQ unomspnoz I mezmchmm noon ma m.vm ooo.moa moan .mm .om nmz wean = v 23 CHmCOUmHR .mmcsmSmM mmma muocmemo modes on ma o.>m oom.noa .mauafl mm: Some Amen omoanea A.na\:memc mmwmamm AmLpCOEv u£WHmR Ummwmamm mmmeamm mmmao Avw>OEmH camv mo mumHm med mmmnm>4 HCQESZ mo open meow gums .Anomazmmmav cavemen: meme an usouo mama omens: .H magma m 22 22m mmma .HH mesh A>mav Hmuuco> mmeeg mumv coumcemsq meted m.om omm.mmn .am enema mmma ocmnm mam Hmmnom H 23 Augmea .um mooznmnm mnocmmmo mmma .ee A>qov Hmuucm> moans mm 2mm compo mH:mH m.mm oom.oma .mH .m mash mmma ummq mam Hamuoo mmma e 22 m>nao pmma ma m.ea oom.mm .52 mesh mmma = m 22 mamamq ma m.mm ooo.ooH mmma .m mmz mmma = v 22 hem umez mmma n mann>nueamum an n.ma oov.mm .mH mash mmmH . o 22 2mm ummm : conmH2 mac me m.mm oom.mv mmme .m 2m2 mmma = v 22 2mm mmnm>mue manna ummz : genome memsom ma m.mm ooo.mm mmmH .m 2m2 mmma = m 22 xeo>manmco ma m.em oov.me mmma .v mmz mmmH = mmmH m 22 memopmm ma m.ma ooo.mma .mH .ma .ummm mmma = m 22 muummsomm ea m.ma oom.mm mmma .ma 223m mmma = 222v m 22 mmzcnnsmz ea o.mH oom.mm mmmH .ma 225m mmmH Hanooomm osmnm A.na\:memv mmemamx AmQMCOEV uflmflmz Ummmmamx mmmmaem mmmau AUm>oEmH CHMV mo momam mad mmeum>4 ueQEdz m0 open meow xuoz .mmscnucou .Aemmaummmav cmmezoflz oxen on ozone mamfi mmxnmz. .N m~&m& emma m 22 mnmemq ma e.ma oom.moe .em muse mmma z m 22 oammmsm 3m2 ma m.mm mmm.eoa emma .m2 2m2 mmmH = Ammmmv m 22 Ahnumw Hmnouomm uflmflm gonna coomcnmsq ma m.mm mam.eoa emmH .m 2m2 mmma mam mmomemm emmH m 22 2Ho>manmno he m.hH Hem.mm .mm mash mmme z emma m 22 mxmouom an m.ma hma.moa .mm mash mmma z m 22 2mm mmnm>mne mcmum I mace ma o.mm mmm.om emma .mm 2m2 mmmH = v a: ham mmno>mne Uswnw AAAU¢V Hmquuom u cocoon mnmzom ma m.am emm.om ammo .Hm 2m2 mmma ammo mam mmomnmm o m 22 Camcoomnz mmma 1 .mmcsmzm2 mfiuma m.mm oom.0ma .mm .NH 2m2 mmma = mmmH m 22 2mm mamazom ma m.mm oom.ooa .NH mash mmme = mmmH m 22 Hmcmu .mm .ea made “new 2mm commusom eelma o.mm oom.mma .mm 2S2 mmma Hmuouomm been A.QH\:mnmv mmmmamm Amflpcofiv uzmfimz vmmmmawm mmnmamm mmmau AUm>oEmH camv mo mumam mm¢ mmmum>¢ Hmnfidz m0 open meow xumz .mmsceucoo .Aemmanmmmflc cmmanoe2 mama an ozone meme mmxnmz .N mNama 11 .22H mamHmcH .mmmueom .nmnm Hmmpm Emnmanpom ma m.mm enm.em amma .m2 2m2 mmma z “>2m4v meocHHHH .2002 Hmnucm> ummnm Hm>m2 mmnmq women m2 e.mm mmm.om emma .02 2m2 mmma mam mmomnmm m 23 Awnnmmv coumcflflmmz noon on commonmsm m m.om oom.mmm emma .poo nmma new Hmmuoe m 22 Amhummv bmma 2mm commesum an m.Hm omm.ovm .mm .m mash mmma = v 23 mama .N mash Amnummv mmcsm3m2 he m.em omm.mom .mm 2m2 mmma z 2>Am4v Hmeucm> meme m 22 2mm mcmm me m.mm nem.noa amma .mm 2m2 mmme mam mmoenmm m 22 Amunmmv mmomecm2 emma on coumcnmsq m e.me ooo.mmm .mm .uemm emma Ame Hamnom Ammmev e 22 somflm2m neon he m.eH mmo.mme emma Hmnouomm unmem .m ~m 225m mmmH mam mmoenma A.na\2memv mmewamm Amzucosv ufimamz mommeamm mmmwamm mmeau AUm>oEmH CHMV mo moeam med mvmme>¢ quESZ m0 @269 new» Mumz .Umscfiucoo .Ahomalmmmap cwmwnoflz mxmq Cm “some mxma UmMHmZ .H wages 12 The remainder of the lake trout samples were obtained directly by the Conservation Department through experimental gill netting and trawling. Gear used by the conercial fishery consisted of gill nets, trap nets, pound nets and trawls. Gill net sires ranged from 2.5 to 5.0-inch mesh and were set primarily for the Great Lakes bloater (Leucichthyg hoyi) and the Great Lakes whitefish (Corgonus clupaaformi_). In Lake Michigan, the minimum legal mesh'siae of gill nets set for whitefish is 4 1/2 inches (stretched measure). This was the most co-only used sire, although some 4 9/16 and 4 3/4 inch mesh nets occasionally were fished. The gill nets used in the chub fishery are limited from 2 1/2 to 2 3/4 inch stretched measure. Because the mesh size used for these two species are quite standard, the data are generally categorised as large mesh (2 4 1/2 inch stretched measure) or small mesh (< 4 1/2 inch stretched measure) gill nets. Incumbent gear (trap nets and pound nets) was used almost exclusively for taking of whitefish, while trawls were used for the co—ercial harvest of alawife and chubs. Departmental gill nets ranged in size from 2.0 to 5.5 inches (stretched measure). The experimental trawling was executed with a 39-foot otter trawl. Each lake trout cath was measured (total length in inches) and examined for fin-clips and lamprey scars. When possible, fish were 13 also weighed and sexed. Scale samples were taken from a representa- tive sine range of the population. In addition, the amount of gear fished, and the location and depth of the set were recorded for each lift. Analysis of Data Specific analyses used are described in detail in each of the appropriate sections. The large amount of data available for this study made the aid of a computer a necessity. The computer system was a Control Data Corporation (CW) 3600, available through the Counter Science Center, Michigan State University. In addition to standard pre-written conuter programs used, several new programs had to be developed specifically for this study. Program source decks can be made available by request to the author or to the Department of Fisheries and Wildlife, Michigan State University, East Lansing, Michigan. in. (I [III GEAR SELECTIVITY Couercial catch records provide a. basis for determining the size frequency of lake trout taken by general gear types. The length distributions of 20,551 lake trout caught in large mesh gill nets, small mesh gill nets, trawls, and trap and pound nets are given in Table 2, and the percentage distributions are shown in Figure 2. Figure 2 clearly suggests a sine specific selectivity of the four gear classifications. The indication is that planted lake trout of yearling size first become vulnerable to the trawl fishery, then to small-mesh gill nets, large-mesh gill nets, and lastly, impounhent gear. The average lengths at capture for age groups I, II and III were found to be 7.9, 11.3, and 15.7 inches, respectively. These averages coincide almost perfectly with the peaks of the catch distribution curves for trawls, small-mesh gill nets, and large-mesh gill nets, indicating a probable corresponding age selectivity for these three gears. Inoundment gear, on the other hand, shows an apparent selectivity for the largest fish of the population, in that the average size of fish reported was approximately 2 inches greater than the average length of age group III fish. The larger size of lake trout reported in trap and pound nets may be due largely to the fact that impoundment gear does not generally kill the entrapped fish, and consequently most sublegal sized fish are returned to the “t0! . l4 15 Hmmom mmm hmmH 0HON 0mNOH meuoe H llll H 0.0m I 0.0m H H Illl. Iltl. 0.0m I 0.0m H llll llll H 0.mN I 0.mN N H H 0.VN I 0.¢m 0 N v 0.mm I 0.mm NH H .llll H OH 0.mm I 0.Nm H0 0H H m 00 0.HN I 0.Hm mmm mm HH 0HN 0.0m I 0.0m 000 0% H 0m omm 0.0H I 0.0H hovH 0m v No HONH 0.0H I 0.0H 00mm 00 h mmH 00mm 0.0H I 0.>H mmom wH mm mmH mmwm 0.0H I 0.0H momm 0H 0m 00m hwmm 0.mH I 0.mH 0mmm m hm me 0m0m 0.¢H I 0.¢H 0mvH m 00 00m NBOH 0.0H I 0.MH 000H w 00 H0m 00 0.NH I 0.NH 00NH m on N00 ¢0m 0.HH I 0.HH N00 H me 0Hm mmw 0.0H I 0.0H mom 00H Hw mmm 0.0 I 0.0 mom 00H 0 HmH 0.0 I 0.0 hmm 00m mm mm 0.0 I 0.> mmH hmH m HH 0.0 I 0.0 mm Hm H .llll 0.m I 0.m mumz vcsom mumz HHHU mpmz HHHO mHmuoe 0cm QMHB mHSQHB Smmz HHwEm Smog mman AmmSUCHV summon Hmuoe mama “mow .500HI000H .mpmc UCSOQ 0cm menu new .mHBMHu .mumc HHH0 SmmE HHmEm .mumc HHH0 Sme m0HMH CH “£0500 weonp mXMH Hmm.0N mo mcoHuanHumHU Sumcmq .N mHQMB Figure 2. 16 Percentage length distribution of lake trout caught in large mesh gill nets (dotted line ......), shall 'nesh gill nets (dashed line ----- ), trawls (solid line ), and inpoundnent gear (dash-dot -.-.-.). _.—____ 17 28 6 2 x . A. so 2 O ’. 0‘ o‘e‘s ‘0‘ 0" n ‘ ‘ 0' \e o o‘. 0‘ a‘el a.‘ ‘0‘9\ oaI.\. ‘0‘. one. \ 1 o .‘e .e 0‘ 2 .\ \\ on 0.0. .\\ l 8 o'.’.’. \\ \w 1 .l:.luoqil...'....ll. II \ o . on... .l'e' ' \ \ I a}. \ ‘. \ \ \ .\ ‘\ _/ . ,I I 16 14 . m 2 .. .z. 1 ... I. W .0 7 o 'r. 1 on, 00’. m? 8 I 3O « PBRCI'TAGE mmnmnmrs BAIEIHEIRIC DISTRIBUTION Because researchers generally lack the vessels and gear for the large scale fishing which is required to study bathymetric distribution, few studies on this important aspect of a fish's life history have been undertaken. In the absence of adequate experinental gear, the author felt that extensive data from a commercial fishery could be useful in studying the depth distribution of a species such as the lake trout which is not open to the fishery but which occupies the ranges of other species which are being exploited, the whitefish and chubs. Reports from the commercial fishermen which contained no lake trout were not available to the author and so were ignored in the analyses. Consequently, because of the incomplete records of fishing pressure, values pertaining to catch per unit effort (CPI) were modified to "catch per unit of effective effort" as described in Hile (1962). lilo supports the use of effective fishing effort for fisheries in‘which most nets are set with the intent and expecta- tion of taking several species sinultaneously. By lile's definition, all the gear lifted by a fisher-an on a particular day is charged to a species if that species is found present in any amount. The author felt that, in the Great Lakes where no effort was being exerted directly toward the taking of juvenile lake trout (they were taken incidentally in gear set for other species), the use of "catch 18 19 per unit of effective effort" is justifiable and would provide the best possible estinate which could be made with incomplete records of fishing pressure. The units of effort used in computation of effective OPE values throughout this paper conforn to those described by Bile (1962). One unit of effort is defined for each of the following gears as: Gill nets. . . . . The lift of 1,000 linear feet of gill 7 netting. Incumbent gear (pound nets and trap nets) . . . . . The lift of one net. Trawls. . . . . . One hour of actual dragging. Table 3 presents the data on bathymetric distribution for 18,342 young lake trout (age groups I, II, and III) captured in Lake nichigan during 1966 and 1967. Effort has been limited to that effort exerted .by gill nets. Data from large and small-nesh gill nets have been combined to provide the widest possible range in depths from which samples were obtained. The depth of water to which the nets were assigned was determined by the mean of the depths at the end of each gang. Catches are grouped by lO-fathom intervals, from 0 to 79 fathoms. Because lilo (1962) reported that the length of time nets are fished does not significantly affect catch per unit effort, the time factor was not adjusted for in this study. Data from the three 20 0.00 0.00 0.0mw 0.000 0.00 m.0mHv 0.00H0 0.00 mHmuOB 0.mH 0.0 0.000 0.00H H.000 0.mm0 0.0H 0.0 HmucHR 0.0 H.00 0.00 0.000 0.0H 0.00 0.mmH 0.0 HHmm 0.0 0.0 0.0 0.00 0.00 0.00H 0.0HHO 0.Hm HmEEdm o.mH 0.mm v.00 H.omm m.mmm m.m¢om m.ovmm o.nm mcflumm UmuMHH #09 mo ummw mo mucmmSO£B 0H.0 00.0 00.0 00.0 >0.H 00.0 00.0 00.0 mQOmmmm HHfl 00.0 IIII. H0.0 H0.H 00.0 00.0 Hh.0 Illl umchE HH.0 00.0 00.0 00.0 00.0 m0.0 0.0 .IIII HHmm .IIII .IIII .IIII 00.0 0m.0 00.0 00.0 mH.0 umEEsm ma.o om.o vo.H «n.o em.a Hn.m 0H.H Hm.o mcfinmm 00I00 00I00 00I00 00I00 00I00 00I00 0HI0H 0H COmmmm Ameonummv among 00 comma .000HI000H CH mnemwmm mSOHum> 0QHMSU .CM0HSUH2 mxmq CH msommv ucmuwmew um mums HHH0 mo ummm 000.H Hmm 030500 usouu mMMH Mo HwQESC m0mum>w ®£B .m mHQMB 21 regions of the lake were conbined but were segregated according to season in order to show any seasonal changes in the depth distribu- _tiom. The greatest concentration of young lake trout occurred at the depth of 20-29 fathoms during the spring, summer, and fall seasons. There is some indication.that the trout move to deeper water in the winter months with the highest concentration at 40-49 fathoms during that period. Lake trout were captured over the widest range of depths during the spring (0-79 fathoms). With seasons combined, the data show that the lake trout, on an annual basis, are found in greatest concentrations at the 20-29 fathom interval and that there were also more at 30-39 fathoms than at 10-19. The present depth distribution appears to differ somewhat from the distribution that had been described by Van.0osten and Fachmeyer (1956) for young native lake trout of the early 1930's. Their study, based on data collected aboard the Bureau of Connercial Fisheries research vessel £21535 during 1930-32, showed the greatest concentra- tion of snall lake trout (mostly 12-15 inches) at depths of 40-59 fathoms for the southern and of Lake Michigan below a line fron Manamiisconsin to Frankfort, Michigan. Above this line, along the north and northeast shores, the greatest abundance was found to be at 30-39 fathoms. 0 1.11.“ N 22 The results of the present study are more closely comparable to those of Dryer (1966) for lake trout in the Apostle Island region of Lake Superior and to the depth distribution of age group I and II lake trout along the southern shore of Lake Superior as reported by Fact-eyer (1956) where the trout were shown to be most plentiful at 20-34 fathoms. Data were analyzed according to depth for 1,548 lake trout which had been sexed. Although males outnumbered females for all but one of the depth intervals, 12 values with at - .01 (Siegel, 1956) indicated that the differences were not significant; males and females apparently have the same depth distribution. Consider- ing that the entire aanple was conposed of hamsters fish, there is probably no biological reason for any differences to occur. GENRAPEICAL MOVEMENTS Just as knowledge of bathymetric distribution of planted lake trout is important for evaluation and'wise management during a rehabilitation program, so is an understanding of the lake trout's dispersal or geographic movement patterns. The extent and direction of movaent away free a planting site will aid in determining where future plants are to be made. Such knowledge is also necessary in estination of survival of the various plants. Pycha, Dryer, and King (1965) presented extensive data on the ‘movaments of hatchery-reared lake trout in Lake Superior. lo comparable study has been made for Lake liehigan. The present study of movement is based upon 20,642 lake trout recaptured in 1965-1967. Figure 3 shows the areas from which samples of lake trout were obtained. No recaptures of lake trout planted in 1967 were reported, thus limiting the study to recoveries of the 1965 and 1966 plants (for specific planting information, refer to Table 1, pages 8-11). One direct method of showing where fish move is by total returns, from the various sampling areas, of marked fish planted in a single area. Tables 4 and 5 give the localities and umber of recoveries by fin-clip and statistical district for the 20,576 lake trout captures in 1966 and 1967. Only 66 recoveries were made in 1965, the year the stocking program began. 23 24 Figure 3. Areas of Lake Michigan from which samples were obtained, 1965-1967. 25 .l’Ia-Cki nae Bri dge ““U9flQma MICH, WIS. ---- .... '.--"'. ---- ...... ....... ........ . . ..-..,.-. l I 0' I‘ ...... . ...... .... .0'”. a... ,. """""" a" n' .- .e """" ''''''''''' uuuuu ........ s. - . . -...- 0.....o _- u ....... ...... fififi Bis Sable Pt. I ....... ...... s.. . Ole. '''''''''' .......... ........ ssssssss '''''''''''''' e ................ ......... ''''''''''''' '''''''''''' PORT /// WASHINGTON; .- sssss euwuuuuesussue' sssss ssssssssssssssssssss ssssssssssssssssss sssssssssssssssssss sssssssssssssssssss sssssssssssssss sssssssssssssssss eeeee as. sssssssssssssssss ........................... ssssssss uuuuu ' HARBOR CHI GAG O ’5: M .MLEH. _____ ______ mo, 0 .mHanHm>m COHpmfihomCH QHHU 0C HO CH0HHO CBOCMCC mo mmHHU Uwz SUHQB Umusummo usouu 0x0H_A7 0000 00 H0 00 00 H00 00¢ 0H0 00H 000H mHmuoe 0 III III III III III III III III III 0 :3 0 III III H III III 0 III III III 0 a?” 000 0 III 00 III III 00H 0 III 0H 0 :2 000 0 III 0 III III 0HH 0 H 00H 0 HEP 000 III III III III III III HOH III 00 0 23 0H III III III 0H III III III III III H EB H00 00 0H 0 III 0H 0 III 0H 0 0 ZS 0HH v 0 III III 0 H H 0 0 0 $2 00H 0H III H 0 00H 0 0 III 0 0 ~00 00H 0 III H 0 H 0 00 w 00 0 22 00H 0H III III III III III 0 00H 0H 0 ZS 000H H0 III III 0 III 0 000 III 000H 0 22 00 H III III 0 III III III III 00 0 :2 00 III III III III III 0 III III 00 H 22 3309 \n/ >0 3 >170 ETC 3. C >m 5 mm. 0 SE 8. mo. 3. mm: 0 EC 3. mm. 3. m0. 3308 0 H22 0 «E. H 23 0 :2 w 0.0,.“ v E,» 0 :2 v E,“ 0 23 mo 0H0» 0000 0 EB mmu¢ Ummb 0CHxnoE 0C0 .mpmm .omu¢ 0CHuC0Hm .mes 0CH¥HmE 0C0 0CHuC0Hm mo H000 OmH¢ .CmmHSUHE mxmq mo mmmum mDOHHm> CH GQUCMHQ usonu mme Umummulmumfiuumfi mo 000H CH mmHH®>ooou mo HwflfidC 0C0 CoHumooq .0 mHQMB .mHQMHHm>w CoHmeHOMCH QHHU 0C HO CHmHuo CBOCXCS mo mQHHU Um: SUHEB meSummu usouu mxma \m/ ooo.0H mom om Hmm 000 mmm mmo m0m oam mow www.mH mamuoe 0 III III III III III III III III III III 0 23 0 III III H III III III 0 III III 0 0 000 000 0 III 0H0 H III H 00 H H 00 v 20 00H 0 III H0 III III III 0H 0 III H0 0 H90 HHO H III III III III III 00H III III v0 0 ER 0 III III III III III III III III III III H 22 00 0 0 HH III 0 H0 0 III 0 w 0 22 0HH 0 00 0 III 00 00 III III 0 v 0 ES 00 0 H III III 00 0 III 0 0 H 0 22 H00 0H 0 0 III 00H 00H 0 0H HH #0 0 22 000 00 III 0 III III 00 H 0H H00 00 w 22 H00.¢H owe m ma N m mom Ha mom 0H moo.ma m eaa 00H 0 III III III 0 0 0 w H 00H 0 ES 000 0 III H 000 III III 0H III H H0 H :2 3308 \n/ >0 .3 >AIC >mIC mm 9... C >m >0 @0- 0 22 mo. 00. 00. 00. m 22 mm. mm. 00. mo. musnmmu 0 SE 0 E; H 23 0 ES “v 0.2 0 23 0 2.2 0. 23 0 22 MO 0 «E m 22 0 :3 mafia. Ummb 0CHMumZ UCm .mumn .mmnd 0CH0C0Hm .0003 0CHMHME 0C0 0CHpC0HQ 00 new» omH¢ .C00H50H2 mme 00 mwmum mCOHMm> CH UmquHm usoup mXMH Umuwmulmumflopmx mo 000H CH mmHH®>OU®H mo HmQEdC 0C0 COHHMUOH .0 mHQme 28 Variations in fishing intensity and the rates of move- 'ment and survival determine how'many fish actually are recovered from the different areas. A measure of relative abundance, comparable in all sampling areas, is needed. Catch per unit of effort values, computed for fish recaptured from a given planting that had been at liberty the same number of years, provide such a measure (Pycha, et al., 1965). CF! values were not used in the present study, however, because effort was too low in the majority of the sampling areas to provide reliable results and because lake trout were taken only as incidental catches in nets set for other species. Bearing in mind that differential fishing intensity and fish survival among areas will have an effect upon the total numbers caught, total catch data alone can still be suggestive of trends of movement. Figures 4-12 show the locations of all returns and probable directions of movement for each of nine fin-clip designa- 'tions. Percentages of the recaptures according to statistical district for each of the fin-clips‘were computed and are presented in.Tables 6 and 7. "LN” Clip - lorth Shore Plant Yearling lake trout having the "LV" (left ventral) clip were released from three locations along the north shore in 1965. The total number planted.auounted to 866,778, representing the largest 29 H0 00 mm Hom 0N0 mme «Hm mmH 000H woodpemomm "Ho Hmnfisz III 00.H III III mm.0 0H.H III III III 0 C: III mm.m0 III III III 00.0 00.0 III 00.0 0 33 III H¢.0 III III III 00.00 00.0 00.0 m0.0 m 000 III III III III III mm.0m III III 00.m m :3 III III 00.00 III III III III III III H 23 0H.0m 0m.m III 00.0 00.H0 00.0 III 00.0H Hm.0 0 20 00.00 III III H .0H mm.HH mm.0 mm.0 00.m 0H.0 0 C: III 00.H 00.0 m0.00 00.0 00.0 0m.H III m0.0 0 H90 III 00.H 00.0 00.0 00.H mH.H 00.HH m0.m m0.m m 2: III III III III 00.0 III 00.0 00.00 00.0 0 2: III III 00.00 III HN.0 00.0 00.m0 III 00.00 m 000 III III 00.NH III III III III III 00.m m 22 III III III III III No.0 III III mm.H .Heae >0 0H >HI0 >mIC mm 00 0 >0 >H 0 22 v 23 0 EH Ho 05 @030. 0.00 0 an m :3 H 03 0 22 H. :2 m :3 m C: .0 E m 22 00 m a: 0000 0CHuC0Hm Mo mmmnd oUmva>OumH QHHUIGHH £00m m0 HQQEdC HwIIHOIIH OmHAm omwmfl amQHHUICHM 050. MO £000 HomeH #UflhpmHU HMUHHmHIIHMUHm Ou. @CflUHOUUm mthHIIHQIHWUmH MO mbmpcmoumm o0 mdflflB 30 00 H00 000 000 000 000 0H0 000 000.0H mmusu Immoom mo Hoflcnsg III 00.0 III III III 00.H III III 00.0 0 H00 III 0H.00 00.0 III 0H.0 00.0H 00.0 00.0 H0.0 0 ER III 00.HH III III III 00.0 00.0 III 00.0 m :3 III III III III III 00.00 III III 0H.0 0 23 III III III III III III III III III H 2. 00.0H H0.m III 0H.m 00.0 00.H III 00.0 m0.0 0 22 00.00 00.H III 00.0H 00.0 III III 00.0 00.0 0 23 00.0 III III 00.00 00.H III H0.H 00.H H0.0 0 22 00.0H 00.H III 00.00 0H.00 00.0 00.0 00.0 00.0 0 2: III 00.H III III 00.HH 00.0 00.0 00.00 00.0 0 a: 00.0 00.0 00.0 00.H 00.00 00.0 00.00 00.0 00.00 m 00H III III III 00.0 00.0 00.0 00.H 00.0 00.0 0 :2 III 00.0 00.00 III III 00.0 III 00.0 00.0 H 22 >0 0H >HIQ >mIQ mm 00 9 >0 >H 0 22 0 :3 m 22 0 23 83 000 0 :2 0 23 H 50 0 22 0 22 0 SB 0 SE 0 :2 0 22 00 m 0H; 0080 0CHpCmHm mo mwmnd .Umum>oomu QHHUICHM Comm mo HmQECC H0000 Ode .000H .mmHHUICHm msu 00 Comm 000 UUHHumHU HMUHpmHumum 0p 0CH©HOUUM mmusummvmh mo m0MpCmoumm .0 mHQMB 31 planting of any fin-clip. Returns tree this plant have been extremely high with 41 recoveries in 1965, 1,868 in 1966, and 13_,962 in 1967. .Although distribution of the recaptures (Figure lo; Tables 6-7) indicate that the majority of returns cane within the general area of planting, a small percentage of the fish have shown extensive novaent. The fact that m 3 received the greatest fishing intensity of any area in Lake Michigan could significantly bias estimates of. relative abundance based solely upon returns for the various senpling areas. Fish of this clip have been recaptured throughout Grand Traverse Bay and all along the eastern shoreline as far south as Benton Harbor. 0n the western shoreline, the LV clip was recaptured as far south as Hilwaukee. Returns from Green Bay show a substantial ascent of lav-lent also into that area. ”U' Clip - Reef and Island Area The "17' (dorsal) clip was represented by a single plant of. 102,000 lake trout released from a ferry off the eastern shore of Beaver Island in 1965. As with the returns free the north shore plant, the najority of the recaptures cane within m 3 (Figure 5; Tables 6 and 7) . The fish becene well distributed throughout the district. Sane noved southward and infiltrated into both arms of Grand Traverse Bay. Still others moved further south along the Michigan -. 32 Figure 4. Localities and nun-her of returns of hatchery-reared lake trout having the "IN" clip. Black circles are planting localities and open rectangles give the ember of fish caught in each area; arrows indicate probable direction of nova-ant. 33 fiackinac Bridge fugx “Gill l/' KKE‘TEB t>D \ . ram um PSTOSKY LiflffiifiUflw MICH. WIS. 11:31-10: :I ma: .5“ ll 1 Guam : BAY r fiRCADIA PORT NH T3 L: {:3' WASHINGTON I ‘* MIL'JAUKErfl is». . m n H01..L:".ND BENTON HARBOR CHICAGO ‘3 - __m__~_jMCH. IND. Figure 5. 34 Localities and amber of returns of hatchery- reared lake trout having the “1" clip. Black circles are planting localities and open rectangles give the number of fish caught in each area; arrows indicate probable direction of novanent. 35 MICH. o ' / WIs, ' - L/ . .. ,- 9 101 It." ‘ . m - ‘ rm ‘5‘.) .3 I»....IO..11 ‘ E] [I] " G 3 " BAY . .'.RC.I=.D1:. PORT HHI 1’1? 1.3-}..2‘ WASHINGTOE - [fl KIL‘JAUKE?) - ‘g 1.: 11011.93“) , .. .23— .e.‘ '.‘. V . CHICAGO 36 shoreline as tar as Muskegon. westward nova-ant appeared to be less extensive with only nine recoveries within Wisconsin waters. These were taken as far south as Algo-a. Five recoveries were nade in 1965, the year of planting. Two of these had traveled outside the ll! 3 boundary into in 5. V 1'31” Clip - Grand Traverse Bay The "RV" (right ventral) clip was represented by 100,500 lake trout planted in the west an of Grand Traverse Bay in 1965 (Figure 6). Twelve recoveries were nade in 1965, all within Grand Traverse Day. In 1966, 79.55 per cent of the recaptures were within Grand Traverse Day. With the exception of a single recovery in Wisconsin waters (Table 4) the r-ainder were taken southward along the Flichigan shoreline to just below 'nolland. Although in 1967, the nunber recaptured within Grand Traverse Bay had increased to 90.5 per cent, there were recoveries reported within every statistical district in nichigan waters. "RP" Clig - Hultiple Locations The "I?" (right pectoral) clip, was represented by 790,000 lake trout released in 1966 free eight locations. Apparently there was very little novuent into Wisconsin waters. lecause these planting sites ranged over a widely scattered area (Figure 7) , very little else can be said about the dispersal patterns. in“ 0111) - Ludigton The "ID-RV" (dorsal and right ventral) clip was represented by 164,990 lake trout planted tron a ferry three to five niles Figure 6. 37 Localities and amber of returns of hatchery- reared lake trout having the "RV" clip. Ilack circles are planting localities and open rectangles give the ntsaber of fish caught in each area; arrows indicate probable direction of nova-ant. lflfilfiflfiUfi, W MICH. , ms. I] 3131303411333". .‘ _I_l GREEN I BAY . ARCADIA Big Sable ?t. PORT NJEI IL LAKE HASHI NG TON MILWAUKEE " _ 1h . aIIOIMLUfD Iii] WIS __ Ill. __Ewmu HARFOR CHICAGOifl ..._..___ ______MICH. IND. Figure 7. 39 Localities and nnnber of returns of hatchery- reared lake trout having the "RP" clip. Black circles are planting localities and open rectangles give the nunber of fish caught in each area; arrows indicate probable direction of movement. MICH. WIS. III SHOE ZI FLT: 2‘: \ - GquI * BAY PORT VASE-111E TON 5‘ “111243115283 . ‘~ ‘4 E] Mixrvfifux. : 11331 I: LII-1;. / l E} M LII I 5:“ h4 p.- [- }—. . ”I, p -; _. ______MICH. IND. 41 southwest of Ludington. How-sents show a trend of even dispersal both north and south along the shore (Figure 8). 0f the total recaptures for the two years conbined, 29.8 per cent were recovered in statistical districts north of ll! 6 while 22.6 per cent were taken south of ll! 6. The difference may be due only to differential fishing intensity. 'fl' Clip - Hilwaukee Reef The "IV" (both ventrals) clip was represented by a plant of 201,530 yearling lake trout released in 1966 frm a ferry in aid- lake near the interstate boundary (Figure 9). Fishing pressure in the area of planting was slight. Only 51 recoveries of this clip were reported. The principal nova-ant out of the area was east- ward end then northward along the nichigan shoreline. Io recoveries were reported in Wisconsin waters. "Ad" 6112 - Mr Peninsula and Kewegge The ”Ad" (adipose) clip was represented by 204,600 lake trout released in 1965 free two Wisconsin lecations. Fish free these plantingsiwere recaptured in every district sanpled with exception of In! 1 and WI! 6. The majority of the recaptures were in the vicinity of the two planting sites. Figure 10 indicates that nove- nent was probably in both directions - north into liichigae waters and Green Day, and south along the Wisconsin shore. Figure 8. 42 Localities and enter of returns of hatchery- reared lake trout having the "II-RV“ clip. Ilack circles are planting localities and open rectangles give the nuber of fish caught in each area; arrows indicate probable direction of meat. 43 r I r d . g.) O {2. H- (I MICH. D WIS, e'-‘. v—‘ir‘ 1.313 321' 14.3.». .-.‘ G “33:1 3 :LRC 1‘ng A. BAY Big Sable 2t. f [HQ [131 L" ' ' 1 :3 1.7.1’ PORT .JLI. WASHIHGTOB. 1.111.111.0123; 711.. .. / , u HOLLAL‘Y‘D ____wu& Ill. [51} .. B31}? 1‘0 .‘1 HfiflBO R - m CdICakUO "f: f% ____MKHL IND Figure 9. Localities and ne‘er of returns of hatchery- reared lake trout having the "IV" clip. Black circles are planting localities and open rectangles give the number of fish caught in each area; arrows indicate probable direction of love-ant. 45 Mackinac Bridge HANISTIQUE MICH. D WIS. MENOHINEE ~ _ GREEN " "‘ BAY . ARCADIA Big Sable Pt. [13 , PORT WHITE LAKE ' ’ 11113311101011.- , _ @1 .Ifip .330me [D ____uns ___ ' Ill II] ‘ . BEH‘ 11 HARBOR CHICAGO :7. '5” ___. ANCHH_ Inn '"‘ ' rim. Ice 46 Localities and amber of returns of hatchery- reared lake trout having the "Ad" clip. Flack circles are planting localities and open rectangles give the enter of fish caught in each area; arrows indicate probable direction of want. 47 ' fiackinac ' Bridge HANISTIiUfi, MICH, WIS. , - I33 GRflEN BAY ARCADIA 8. , Big Sable 3t. PORT 21111 ~11: 1.9.112: ' WASHINGTON E3 111' 1.11.10.11.91 e 110111.111) 321111011 HARBOR MICH. IND. 48 "LP“ Clip - Door Peninsula andlgwaunee The "LP" (left pectoral) clip was represented by 369,100 lake trout released in 1966 from two sites along the Door Peninsula and a third site at Kewaunee, Wisconsin (Figure 11). Distribution of recoveries was very sinilar to lake trout having the "Ad" clip. The najority of sa-ples were recovered in the localities of the planting sites. A few fish had noved into liichigan waters, apparently following the shoreline around both ends of the lake. In contrast to the "Ad" clip, very few fish of this group dispersed into waters of Green Bay. 4 MW Glip - Green M The "D—LV" (dorsal-left ventral) clip was represented by 190,300 yearing lake trout released in Green Bay in 1966. Recovery data from this plant indicate a northward trend of nov-Ient, with the majority of recaptures nude within ll! 1. Snell numbers noved along the northern shore into Hichigan waters (Figure 12) . There was little evidence that the lake trout noved southward along the Wisconsin shoreline. In general, dispersal appeared to be slight, with only 16 recoveries outside of Green Bay waters. Discussion of Hove-ants Previous documentation of lake trout novuent patterns in Lake Hichigan is linited. A study by Snith and Fan Oosten (1940) , based on 1416 tagged native lake trout averaging 12.8 inches, indicated Figure 11. 49 Localities and nunber of returns of hatchery- reared lake trout having the ”LP“ clip. Black circles are planting localities and open rectangles give the nunber of fish caught in each area; arrows indicate probable direction of nova-eat. 50 liaclri 2110 Bridge 909 D \ MICH_ WIS. ‘ n 1131101211125: MESH ‘\ /' Egg; 1 . n. ‘7PII" GREEN fffifl BAY 1. III PORT 211-1111;: 1.3.1:: WASHINGTON IIILIIIIUKE-i‘h ., II] n HOLLAI-ID H l h E] ,. BENT-C7}? HARBOR CHICAGO E 31.. --—— ~—_*fi.LC_H_- '_ mo. “'— Figure 12. 51 Localities and nowhere of returns of hatchery- reared lake trout having the ”D-LV" clip. Black circles are planting localities and open rectangles give the number of fish caught in each area; arrows indicate probable direction of novenent. MICH. WIS. \ GREEN ” BAY PORT ’YASHINGTOH- IIILIIAUKEB of“ CHICAGO I; _ # In // I; II PETOSKY n ‘0 9 . 52 Mackinac Bridge A " Big Sable Pt e .WHITE LAKE a HOLLAND BENTON ’ HARBOR nucu.__ INQ no...“ 53 that after one year of liberty 73 per cent of the recaptures'were still within 25 stiles of the release site. In the present study, the najority of'innature hatchery-reared lake trout appear to have renained in the general areas of release even after three years at liberty. however, movement which did occur away fronIplanting sites was very extensive with distances as great as 290 niles between point of release and point of recapture. Hovenent away from planting sites tends to be a gradual dispersal in directions along preferred depth contours; nova-ant to offshore waters was linited. The one case where offshore nove— nent was exhibited‘was the north shore plant (an 3) which showed dispersal to nearly all areas within the district, both along the shore and offshore. Illature lake trout tend to inhabit water depths of 10-50 fathons (range of greatest abundance: 20-29 fathons); they were seldon taken in depths greater than so fathons (rm. 3, page 20). Water depth in In! 3 is relatively shallow (approxinately 90 per cent of the area is less than 40 fathoms), whereas the majority of the other districts have depths of 10-50 fathons only near the shore. chha, et al., (1965) found concentrations of planted lake trout in Lake Superior also linited to the areas along the shoreline or at least in waters of less than 50 fathoms. It appears that depth preferences are.inportant in geographic distribution. The contribution of Michigan planted trout to‘Wisconsin's total catch appears to be substantial, accounting for 36.5 per cent of 54 Wisconsin's total recaptures. Wisconsin releases ends a lesser contribution to the total catch of fish within Michigan waters amounting to only 2.0 per cent. Total recaptures were nuch greater in Michigan waters, however. The total releases in Hichigan waters were 2,226,698 during 1965 and 1966 while only 764,000 were released in Wisconsin. SIZE Arm ‘With infornation about the fin-clip and the date of recapture, each fish can be assigned to an age group. Table 8 presents the length distribution by age groups for 20,015 recaptured lake trout having fin-clips that corresponded to specific plantings during 1965 and 1966. Each age group represents fish of a wide range of lengths. This wide range can be largely explained by the sanpling season being extended throughout the year of growth. Scan of the extrenely large fish assigned to age groups I and II any be the result of recaptures of narked fish from a few experinental plants nade during the years of 1960-1962. LV, 2!, LP, and RF are clips which had been used in these earlier plants and duplicated in either 1965 or 1966. The analysis was executed by a conputer progran7with no loans of ' detecting and eliminating these larger fish. Because of errors in reporting, and occasional nis-clipping in the hatcheries, one would not expect this nethod of assigning ages to fish to be conpletely accurate. However, the extreme values should not significantly bias average lengths at tilIIOf capture for the individual age groups. The average lengths for age groups I, II, and III were 7.93 inches, 11.28 inches, and 15.68 inches showing increments of 3.35 and 4.40 inches for the second and third years, respectively. These 55 56 Table 8. Length distribution of the age groups of marked lake trout recaptured in Lake Michigan, 1966 and 1967. Total Age Group1 Length (inches) I II III Totals - 5.9 26 1 27 — 6.9 154 12 166 — 7.9 219 53 2 274 - 8.9 142 161 2 305 9.9 93 385 10 488 10.9 79 762 33 874 11.9 49 1083 110 1242 12.9 11 731 319 1061 13.9 9 461 66 1436 14.9 7 287 2017 2311 15.9 1 148 3352 3501 16.9 1 55 3457 3513 17.9 33 2428 2461 18.9 18 1341 1359 19.9 2 6 628 636 29.9 4 250 254 21.9 2 83 85 22.9 11 11 23.9 6 6 24.9 1 1 25.9 2 2 26.9 1 1 27.9 1 1 Totals 796 4203 15016 20015 1 Some of the extreme values for age grQUps I and II may be the result of recaptures of marked fish of experimental plants of 1960—1962. LV, RV, LP, and RP are clips which had been used in these earlier releases. 57 there-eats calipers quite closely to values to be brought out in e 1ster discussion of computed growth. Gm Cable (1956) confirmed the validity of the reading of annuli on scales as a method of aging lake trout. As a check on the use or marks on planted lake trout for determining age and for back- calculations of length, scale samples were collected from 402 lake trout captured in Hichigan waters of Lake Michigan. These fish were captured in a variety of gears. 0f the total, 184 (45.8 per cent) ‘were taken in small-mesh gill nets, 141 (35.1 per cent) in largedmesh gill nets, 66 (16.4 per cent) in trawls, 9 (2.2 per cent), in na- pound-eat gears, and 2 (0.5 per cent) in an unknown gear type. Samples were combined to minimize bias due to gear selectivity and to provide the widest possible range of lengths. The total length of each fish was determined to the nearest 0.1 inch. The length composition of the lake trout used in the growth study is given in Table 9 for each of the five statistical districts from which samples were obtained. ‘ggdy-Scale Relatigg and Calculation of Growth The scales for the growth study'were taken from the area below the origin of the dorsal fin and just above the lateral line. Cellulose acetate impressions were made of all scales using a scale press of the type described by Smith (1954) . The impressions were magnified 80! and projected onto a frosted glass screen by an Bberbachwmicro- projector. Tor each of the scales, the total scale diameter and the 58 59 Table 9. Length distribution and area of capture for 402 lake trout from which scale samples were obtained. Length Statistical District Interval (inches) MM 3 MM 4 MM 5 MM 7 MM 8 Totals 5.0 - 5.9 6.0 — 6.9 1 1 2 7.0 — 7.9 5 12 17 8.0 - 8.9 16 16 32 9.0 - 9.9 5 1 20 26 10.0 — 10.9 19 l 4 3 27 11.0 - 11.9 39 4 2 11 4 60 12.0 - 12.9 25 4 2 7 38 13.0 - 13.9 40 4 5 1 50 14.0 — 14.9 42 2 44 15.0 — 15.9 18 2 20 16.0 - 16.9 18 2 20 17.0 - 17.9 28 28 18.0 — 18.9 21 21 19.0 - 19.9 9 2 11 20.0 — 20.9 2 2 4 21.0 — 21.9 1 1 22.0 - 22.9 23.0 — 23.9 1 1 Totals 288 24 5 28 57 402 60 diameters at each of the annuli were measured to the nearest milli- ‘meter along an imaginary line that passed through the focus and bisected the anterior and posterior fields. The body-scale relation was determined from the average diameters of two scales from each of 392 fish. Ten samples (2.5 per cent) 'were discarded because of poorly defined annuli or too few scales. Van Oosten and Eschmeyer (1956) and Cable (1956) supported the use of scale diameters rather than scale radii for lake trout growth calculations. Van Oosten and.Bschmeyer state that lengths computed from radial measurmaeus have been found to be too low in nearly all species of fish. In addition, diameters tend to be less variable than either the anterior or posterior radii (Van Oosten, 1929). Rahrer (1967), also using scale diameters rather than scale radii, found the body-scale relationship for lake trout in Lake Superior to be curvilinear. The least-squares technique showed the relationship in the present study to be more strongly linear than curvilinear with simple correlation coefficients of 0.9278 and 0.9095, respectively. The linear equation describing the.means of magnified scale diameters to the total body length was found to be: L - 0.538 + 0.0788 8 where L is total length in inches, 8 is the magnified scale diameter in millimeters, 0.0788 is the slope of the regression, and 0.538 is the y-intercept value. 61 Back-calculated lengths were derived from the direct proportion equation: L' - c +'g': (L-C) where L' equals the body length when annulus x was foamed, 3' is the field within annulus x, s is the total scale diameter, L is the body length at capture, and c is the y-intercept (alpha) from the total length-scale diameter equation above. The average lengths at capture and back-calculated lengths for age groups I, II, and III (year classes combined) are shown in Table 10. Growth data were analysed separately for the upper and lower regions of Lake Michigan; computations were also made with all samples combined. The upper region is represented by samples from Statistical Districts w 3, ll! 4, and Ill 5. The lower region had fish fraa Fl! 7 and m 8. lots that calculated lengths for age groups I and II from.the lower region‘were considerably smaller than corresponding lengths for the upper region. These differences may be a result of gear selectivity rather than actual differences in growth rates. As evidence of this, one would expect the length at the end of the first year of life to be approximately the same for both regions as a result of nearly identical rearing histories prior to planting. Because no age group III fish were represented in samples free the lower region, no comparisons of growth histories can be made between the two regions for this age group. 62 gm.va gm.oa m¢.6 mucmfimnuca m0 coapmfiadm Eon“ gumceq 00.6 Hm.m m¢.6 gnocma cfl xpBOHm mo pcofimnucfl cmmz mod Hmm mam mcmsaumom no honeys ma.ma mH.HH mH.h 6H.na moa oocfiflgou III III III III III HoBOq 64.64 0H.HH 6H.s 6H.5H mos Home: HHH mo.m INN.6 06.NH IMHMI. ooCHQEoo mm.m mm.m 6h.HH gm HoBmA HH.OH Hm.6 ms.ma 66H some: HH mm.m 06.6 as Umcfinfioo mh.m mh.m Hm Hosea 66.6 nm.m om moods H m m H mHSmeu p6 Sumcmq mcmEHUmmm Qsouw meH m0 ommum>4 m0 Honfisz 66mm mmfi Hook m0 one no summed Umpmasuamo .mogucfl ca 6H6 msumcma “oocwflfiou mum mommmao meow .HHH 6cm .HH .H mmsoum mom “usonu mxma ooxnmfi mo meadow exp :0 Haoccm m0 mumpoEMHo EOHM cospHOQOHm pomHHU ma ooumasuamo mfipmcma 6cm mushmmu p6 flpmcma H6809 .OH manoe 63 The data show that with all samples combined, the calculated lengths for a particular year of life become progressively higher 'with increasing age. Such an occurrence is the inverse of what is consonly described as "Lee's phenomenon." Back-calculated lengths computed by Cable (1956) showed decreasing values with increasing age (Lee's phenomenon) for age groups III to VI. This was explained to be the result of selective mortality for the larger individuals by both the sea lamprey and the co-ercial fishery. In contrast, age groups I, II, and III in the present study are not being subjected greatly to either of these selective factors' because they are still too small for heavy lamprey predation and are not being exploited by the fishery. The inverse of Lee's phenomenon, then, might be exhibited in these samples because of selectivity by gears. The majority of age group I fish were obtained by trawls while groups II and III fish were captured in gill nets (refer to earlier section for the selective action of these gears). Gill nets would tend to select for faster growing fish of these lower age groups than do trawls. In view of the above factors, the author believed the best overall estimate of growth rate for juvenile planted lake trout to be the mean increments of growth for each year of life as are given in the lower portion of Table 10. This method shows the mean annual incraents of growth for the first three years of life to be 6.43, 3.91, and 4.00 inches. Cable (1956) reported increments of 5.9, 2.8, and 2.5 inches for age groups I, II, and III while Van Oosten 64 and Eschmeyer's (1956) data indicated corresponding values of 3.4, 3.7, and 3.0. Fish studies by Cable were principally recoveries fromxplantings of hatchery-roared fingerlings; data from‘Van Oosten and Bschmeyer were for native lake trout. The mean lengths at the end of successive years of growth‘were obtained by the summation of mean calcuaated increments of length. Table 11 compares the mean lengths of the present study to those of Cable and Van,Oosten and Eschmeyer. For areas combined, lengths 'were greater for each year of life during the present study than for either of the previous reports (for a graphic illustration of this comparison, see Figure 13) . The increased rate of growth exhibited by lake trout of the present study over growth rates in the 1920's and 1940's may reflect an advantage attained by the longer period of hatchery growth and the subsequent increased length at age I. This advantage obviously- carries over into later years as is evidenced by the differences at age III. ‘Hhile the differences in length at age I can be explained by hatchery growth, the increased increments of growth for the second and third years shown by the current study over previous periods may be due partially to other factors. Low lake trout population levels during the present study period could result in less intraspecific competition than occurred during earlier periods before the decline 65 Table 11. Growth of lake trout for northern Lake Michigan, southern Lake Michigan, and areas combined. All values are from grand average increments based on calculated lengths at the end of the indicated years of life. Year Total Length (inches) from Area and Author Classes Summation of Increments 1 2 3 Northern L. Michigan Cable (1956) MM 4-6 '44-'46 6.9 10.0 12.8 Hesse (present report) MM 3, 4, and 5 '64—'66 6.8 10.7 14.7 Southern L. Michigan Cable (1956) MM 7—8 '44—'46 5.6 8.8 12.1 Hesse (present report) MM 7—8 '64—'66 5.8 9.2 All Areas Van Oosten and Eschmeyer (1956) '22—'30 3.4 7.1 10.1 Cable (1956) MM 4—8 '44—'46 5.9 8.7 11.2 Hesse (present report) MM 3, 4, 5, 7, and 8 '64—'66 6.4 10.3 14.3 66 Figure 13. Calculated growth in length (from su-nation of increments) for the present study (dash-dot line), from Cable (1956) (solid line), and from VanTOosten and Eschmeyer (1956) (dashed line). 67 16- 14- 2 1 TOTAL LENGTH In I'C'BS o 8 6 I. NOEL”! 68 of the stocks. Other drastic ecological changes which have taken place in Lake Michigan such as the severe changes in species composi- tion (Smith, 1968) undoubtedly affect present lake trout growth. LENGTH-WEIGHT RELATION Data on both length and weight were obtained for a total of 2,253 lake trout over the period of study. These samples were collected with a variety of gear types and include recaptures during each of the seasons. Lengths and weights were taken by Department personnel either during ou-board and dock inspections of commercial fishing vessels or were obtained after the samples had been brought to the laboratory. The equation used to express the lengthaweight relation in fishes is: Logldw - Logloc + a L°810L where‘fl is weight in ounces, L is total length in inches, c is the y-intercept, and n is the slope of the regression. Equations describing the relationship for the three general lake regions of. Lake Michigan and for the total sample are presented in Table 12. The equation found for the upper Lake‘Michigan sample compared very closely to the equation reported by Cable (1956) for a sample of 1,197 planted lake trout from northern Lake'Michigan: Logldw - -2.4698 + 3.1125 LogloL The study by Cable was of planted fish of year classes 1944, 1945 and 1946. Recoveries of these plantings were made between the years of 1947 and 1952, a period characterised by the crash of the lake 69 70 mmmm.o daemon moma.m + sooa.mn n soaaoa mmmm mechamm Uncensoo mssm.o daemon 4mm6.m + Hana.mn u season 46 camcoomaz mm6m.o daemon wmom.m + mm6v.mu u soamoq 646 mean mason Hasm.o doomed smsa.m + 4644.Nu u soamoq mmma nan “mono m coflnmfimm unmamzutnmcmq been 60 some nonfidz .ucmaUmemoo cofluMHmunoo n m .omCHQEOU mcowmmn now Oman “cwoflflofiz exmq mo mnou63 Camcoumflz one .QOHomH HmBOH .cowmmn Hoods exp CH odouu mxoa How mmfigmcoflpmaoh pfimflmzlfipmcmq .NH canoe 71 trout stocks in Lake Michigan. An earlier study by Escbeyer and Van Oosten (1956) provides an estimate of the relationship during the pre-lamprey period. Data for the study were from lake trout collected during the years of 1930-32. The resulting equation was as follows: LogloW - -5.4652 + 3.1377 LogloL where W is weight in grams, and L is total length in millimeters. Samples were collected from extensive regions of Lake Michigan. Figure 14 shows a comparison of the above relationship to the relation- ship presented in the current study for regions combined. The curves indicate that the lake trout planted in Lake Michigan since 1965 are more robust throughout the length range sampled than the native lake trout of the earlier study of Van Oosten and Eschmeyer. The relationships for the three lake regions in the present study show a marked difference between fish collected in Michigan waters as compared to fish from Wisconsin waters of Lake Michigan. late that the value of "a" is greater than 3 for sampled from the upper and lower regions, indicating that these fish became progressively more robust with increase in length. The Wisconsin sample, on the other hand, has an "a" value of 2.8224. This shows that these lake trout are neither as robust as lake trout of the other two regions nor do they conform to the "cube law." ,The differences may result from the smaller sample size (54 observations) from which the relation- ship was computed for the Wisconsin region. Further study is Figure 14. 72 Lengthdweight relations of lake trout of Lake Michigan. The solid line represents the relation presented in the present study for regions combined: LogldW - -2.4007 + 3.1309 LogloL The dots about that line show the empirical weights. The dashed line describes the relation presented by Van Oosten and Fschmeyer (1956): LogldW - -5.4652 + 3.1377 LogloL (The upper equation was based on length in inches and weight in ounces; the second equation was in millimeters and grams.) Hint-4N8 UDUICDIICICD lira 42 38 30 26 22 18 14 10 73 m m m e A 10.0 12.0 14.0 TOTAL LENGTH II INCIES 16.0 18.0 74 necessary to determine more specific explanations for the differences. Smith (1956) points out that the relation between length and.weight in a population can vary with respect to sex, season, method of capture, and year of capture. In order to segregate the data according to all of these variables, much larger sample sizes would be necessary. PREDIJIOI I! SEA LAHPREYS Predation by the sea lamprey, Petrogyzon.marinus, was one of the primary causes of the decline of the lake trout fishery in the 1940's. In order to evaluate the success of the lamprey control program which began in Lake Michigan in 1960, close attention has been giveh to the incidence of lamprey scarring in all samples of lake trout since their reintroduction in 1965. Tables 13a, 13b, and 13c summarise the lamprey wounding rates for 20,541 lake trout collected during 1966 and 1967. The data are presented according to total length of fish (l-inch intervals) for each year by regions of the lake. No attempt was made to distinguish between fresh and old scars. Records from upper Lake Michigan showed the heaviest scarring rates of the three lake regions for both years, with overall rate of 1.4 per cent in 1966 and 4.5 per cent in 1967. In each of these years there appeared to be a gradual increase in the rate of scarring 'with an increase in the length of the fish. In 1966, however, lake trout as small as 9.0 inches showed lamprey scars, while in 1967, no scarring was reported on fish less than 11.0 inches. The average size of lake trout present in the lake in 1966 was less than in 1967, thus possibly indicating that the lampreys only attack the smaller individuals when there is an absence or shortage of larger lake trout. 75 76 6.6 666 6606a ¢.H om 660m mHmnoe III III III III III III 6.66 I 0.66 III III III III III III 6.66 I 0.66 0.0 0 H III III III 6.66 I 0.66 0.0 0 6 III III III 6.66 I 0.66 0.0 H 0H III III III 6.66 I 0.66 6.6 6 66 III III III 6.HN I 0.HN 6.6 6H 6H6 0.0 0 H 6.06 I 0.06 6.6 06 666 0.0 0 m 6.6H I 0.6H 6.6 66 6H6H 0.0 0 6 6.6H I 0.6H 6.6 H6H H6vm 0.0 H 0H 6.6H I 0.6H 6.6 006 6666 6.6 H 6H 6.6H I 0.6H 6.6 66H 6666 6.6 6 N6 6.6H I 0.6H 6.6 H6 HOHm 6.6 v 06H 6.6H I 0.¢H 6.H 6H m60H 6.H 6 66m 6.6H I 0.6H m.H 6 666 H.H 6 66m 6.mH I 0.NH 6.0 H 666 v.H 6 66m 6.HH I 0.HH 0.0 0 66H 6.0 6 N66 6.0H I 0.0H 0.0 0 6HH 6.0 6 66m 6.6 I 0.6 0.0 0 66 0.0 0 mNH 6.6 I 0.6 0.0 0 6 0.0 0 H6 6.6 I 0.6 III III III 0.0 0 66 6.6 I 0.6 III III III 0.0 0 6 6.6 I 0.6 mnmom mnmom SmHm mumum mhmom zmHm SuHB QuHB 60 Spas nuHB mo ucoo mom Hmflsdz “60532 ucou Mom H6085: “@9852 AmoQUCHV H6>HmucH common 666H 666H .mH6>uoucH £u6cmH SUCfiIH on 6CH0H0006 omuhHoco one sumo .666H one 666H .comfisoHE oxmq Home: CH ownsummo poouu mme co OCHnnwom monEoH mo mocooHocH .enH oHfloe 77 0.0 0 666 6.0 6 666 mHmuoe III III III 0.00H H H 6.66 I 0.66 III III III 0.00H 6 6 6.66 I 0.66 III III III III III III 6.66 I 0.66 III III III III III III 6.66 I 0.66 III III III 0.0 0 H 6.66 I 0.66 III III III III III III 6.H6 I 0.H6 III III III III III III 6.06 I 0.06 0.0 0 H III III III 6.6H I 0.6H 0.0 0 6 0.0 0 H 6.6H I 0.6H 0.0 0 6 III III III 6.6H I 0.6H 0.0 0 w 0.0 0 v 6.6H I 0.6H 0.0 0 6 0.0 0 6 6.6H I 0.6H 0.0 0 6 0.0 0 6 6.¢H I 0.6H 0.0 0 6H 0.0 0 6 6.6H I 0.6H 0.0 0 66 0.0 0 6H 6.6H I 0.6H 0.0 0 0HH 6.H H 66 6.HH I 0.HH 6.6 6 6m 6.6 6 m6 6.6H I 0.66 0.0 0 HH 0.0 0 66 6.6 I 0.6 0.0 0 v 0.0 0 6HH 6.6 I 0.6 0.0 0 6 6.0 H 606 6.6 I 0.6 III III III 0.0 0 66H 6.6 I 0.6 III III III 0.0 0 6H 6.6 I 0.6 menom mnnom £666 mumom mhnom SmHm suHB 56H: 60 SMHB £pHS mo pnoo mom Hoflfinz 609852 undo Mom MmQEfiz HoQEdZ AmononHv H6>HounH summon 666H 666H .mH6>HounH SumnoH SonHIH op 6nHonooom omuhHonn 6H6 upon .666H one 666H .nnmaSUHZ mind HoBOH nH nonnpmoo #5066 oon no 6anumum mmHmEnH mo oonooHonH .an oHQoB 78 6.H OH 066 0.H 6 666 6H6#OB III III III III III III 6.66 I 6.66 III III III III III III 6.66 I 0.66 0.0 0 H III III III 6.66 I 0.66 0.0 0 6 III III III 6.66 I 0.66 0.0 0 H III III III 6.66 I 0.66 6.6 6 66 III III III 6.H6 I 0.H6 6.6 6 6% III III III 6.06 I 0.06 6.H H 66 0.0 0 H 6.6H I 0.6H 6.H H 66 0.0 0 6 6.6H I 0.6 0.0 0 6w 0.0 0 HH 6.6H I 0.6H 6.6 6 66 6.6H 6 6H 6.6H I 0.6H 6.6 6 H4 6.6 H 66 6.6H I 6.6H 0.0 0 66 0.0 0 66 6.6H I 0.6H 0.0 0 6H 6.6 6 H6 6.6H I 0.6H 0.0 0 6H 0.0 0 n6 6.6H I 0.6H 0.0 0 6HH 0.0 0 666 6.HH I 0.HH 0.0 0 6HH 0.0 0 6HH 6.0H I 0.0H 0.0 0 6 0.0 0 66 6.6 I 0.6 0.0 0 H 0.0 0 H6 6.6 I 0.6 0.0 0 H 0.0 0 6H 6.6 I 0.6 III III III 0.0 0 6 6.6 I 0.6 0.0 0 H 0.0 0 6 6.6 I 0.6 unnom muoom £666 whoom mhmom 5666 anB nuHB 60 £663 SuHB mo pnou Mom Hmflfidz Hmflfinz pnoo Hon HQQESZ HoQEdZ AmmnonHv H6>noan Somnma 666H 666H .mH6>HmnnH SpmnoH nonHIH on 6nHouooom ooumHmno 6H6 ounq_ .666H one 666H .no6HnoH2 oxen mo mump63 nHmnoomHE nH omusumno psonw oon no 6anhoom mommaoH mo oonmoHUnH .ofiH mHfloB 79 Although the sample size was small for each of the years in lower Lake Michigan, scarring appeared to be very light. The overall scarring rate was 0.7 per cent in 1966 and 0.0 in 1967. However, the average size of fish captured was also considerably less than in the upper region. Data from Wisconsin waters of Lake Michigan also indicated very light scarring in 1966 and 1967, with 1.0 and 1.6 per cent, respectively. In 1966, no lake trout smaller than 13.0 inches bore lamprey scars, and in 1967, no scars were reported on trout smaller than 15.0 inches. For the larger sized fish, however, scarring rates were quite comparable to rates for the sue length intervals reported for the upper region. Combining the lake regions and years, sublegal sised lake trout (<17.0 inches) showed a scarring rate of 3.0 per cent, while legal sized trout had a rate of 6.3 per cent. According to Crowe (pers. comm), the scarring rate of the legal-sized lake trout at the time of the population crash was approximately 25-30 per cent. Ivan though the present data indicate a scarring rate much lower than this, no definite conclusions can be drawn as to the effectiveness of the lamprey control program in Lake Michigan until more of the fish reach a size which is vulnerable to predation. SWY AND CONCLUSIWS The study was based upon recoveries of 20,642 juvenile lake trout during 1965 through 1967. The majority of the data came from reports of incidental catches of lake trout in conercial gear set for other species. Because complete information was not always available as to type or amount of gear used, depth of recovery, fin-clip designation, weight, sex, or lamprey scarring data, the total numbers of fish used in the various analyses differed from one analysis to another. A suImsary of sample sixes is as follows: Gear selectivity, 20,551; Bathymetric distribution, 18,342; Geographic mow-sent, 20,642; Sise at capture by age group, 20,015; lack-calculated growth, 402; Length-weight relation, 2,253; Predation by sea lampreys, 20,541. 1. The size frequency distributions of incidental catches of lake trout in four co-ercial gear types show a definite sise specific selectivity. Imunhent gears took the largest lake trout; large-mesh gill nets, small-mesh gill nets, and trawls took progressively smaller fish. There appeared to be a corresponding age selectivity for the latter three gears. 2. The depth distribution was computed according to season by lO-fathom intervals based upon effective Cl"! in co-ercial gill nets. Lake trout were recaptured throughout a range of 0-79 fathoms. The greatest concentration during spring, smer, and fall seasons occurred at 20-29 fathoms. In the winter, the greatest concentration 80 81 was at 40-49 fathoms. lathymetric distribution was not significantly different between males and females (szalues; K- .01). 3. Geographical movmnent away from planting sites was a gradual dispersal in directions along preferred depth contours with very little movement to offshore waters. Movement did not appear to be either clockwise or counterclockwise. The majority of lake troutremained within the general areas of release even after three years at liberty. However, nov-Ient which did occur away from planting sites was very extensive with distances as great as 290 miles between point of release and point of recapture. 4. Michigan planted trout accounted for 36.5 per cent of Wisconsin's total recaptures while Wisconsin releases contributed only 2.0 per cent of the recoveries within Michigan waters. lonevnr, far greater nI-bers of trout have been planted in Michigan waters than in Wisconsin waters. 5. The length distribution of the age groups I, II, and III show a wide range within an age group and substantial overlap between age groups. This was probably due to the combining of samples over the entire growing season. The average lengths at capture were 7.93, 11.28, and 15.68 inches for the three age groups. 6. The body length-scale diameter relationship was described by the linear equation: L - 0.538 + 0.0788 8. This provided the y-intercept value of 0.538 inches to be. used as the correction factor in the back-calculation of growth. The mean calculated increments of growth for the first three years of life were found to be 6.43, 82 3.91, and 4.00 inches. Summation of these increments yielded total back-calculated lengths of 6.43, 10.34, and 14.34 inches. Compared to growth rates during periods of pre-lamprey and lamprey abundance, the present growth rate was considerably greater. The author believes that the increased growth is probably due to a combination of factors: 1) advantages gained during a longer hatchery existence, 2) less interspecific and intraspecific competi- tion than occurred prior to the decline of the lake trout stocks, and 3) to extreme changes in species composition‘within the Great Lakes. 7. A lengthdweight relationship based on samples from upper Lake Michigan compared closely to a relationship described by Cable (1956) for lake trout in that area during the 1940's. The equation based on the entire sample of fish for which length and weight had been recorded indicated that lake trout planted in Lake Michigan since 1965 are more robust throughout the length range sampled than were native lake trout of the 1920's. Fish recaptured inIMuchigan.waters appeared to be more robust than those from Wisconsin waters. 8. Incidence of lamprey scarring was slight for all samples. Sublegal sised lake trout (< 17.0 inches) showed a scarring rate of 3.0 per cent, while legal trout had a rate of 6.3 per cent. The author wishes to present several inherent problems researchers encounter when using commercial fisheries data for 83 biological analyses: a. Fishing intensity is not equal among geographical areas. b. Sampling is limited to established fishing grounds of commercial fishermen. c. Gear types used in the various areas vary with the species being harvested. Because of unequal vulnerability to the different gear types, data becomes difficult to interpret. d. use of incidental catch data, such as for the lake trout, may not be as reliable as if the species under study was being specifically sought. Commercial fishermen fish their gears in areas of greatest abundance of the particular species they desire. This may or may not be within the optimum range of the species taken incidentally. e. Data reported by lay people may tend to lack the accuracy, consistency, and completeness that can be attained by trained personnel. Even though the above factors limit the interpretation of commercial data, the fact that the commercial fishery provides a 84 readily available and economical means of sampling extensive areas far overshadows the negative aspects. 0n the other hand, the limitations illustrate the need for increased systematic sampling through the use of well-equipped research vessels. LITERATURE CITED Buettner, Hoivard J. 1965. Co-ercial fisheries of the Great Lakes, 1879-1963. Fish and Wildl. Serv. Stat. Digest lo. 57. Cable, Louella E. 1956. Validity of age determination from scales, and growth of marked Lake Michigan lake trout. 0.8. Fish and Wildlife Serv., Fishery Sull., 57 (107):l-59. Dryer, William R. 1966. Rathymetric distribution of fish in the Apostle Islands region, Lake Superior. Trans. Amer. Fish. Soc., 95(3):248-259. Rscluseyer, F.H. 1956. The early life history of the lake trout in Lake Superior. Michigan Dept. Conserv. Instit. Fish. Res., Misc. Publ. 10, 31 p. Eschmeyer, NI. 1957. The near extinction of lake trout in Lake Michigan. Trans. Amer. Fish. Soc., 85:102-119. Hile, Ralph. 1962. Collection and analysis of co-ercial fishery statistics in the Great Lakes. Great Lakes Fish. Cami” Techn. Rep. 5, 31 p. Mile, Ralph and Howard J. Buettner. 1954. Statistics of the lake trout fishery of Lakes Huron, Michigan, and Superior, 1949-53. Great Lakes Fishery Co-ittee. Minutes ofAnnual Meeting, St. Louis, Mo., pp. 36-40. Hile, Ralph, Paul H. Bschneyer, and George F. Lungsr. 1951. Status of the lake trout fishery in Lake Superior. Trans. Amer. Fish. Soc., 80:278-312. Moffett, James W. 1957. Recent changes in deep-water fish popula- tions of Lake Michigan. Trans. Amer. Fish. Soc., 86:393-408. chha, R.L., W.R. Dryer, and G.R. Ring. 1965. Movmnents of hatchery-reared lake trout in Lake Superior. J. Fish. Res. 8d. Canada, 22:999-1024. Rahrer, Jerold F. 1967. Growth of lake trout in Lake Superior before the maxim:- abundance of sea lampreys. Trans. Amer. Fish. Soc., 96(3):268-277 85 86 Shetter, David S. 1951. The effect of fin rmaoval on fingerling lake trout (Cristivomer namaycush). Trans. Amer. Fish Soc., 80:260-277 Siegel, Sidney. 1956. Nonparametric statistics for the behavioral sciences. McGrav-nill Book Company, Inc., New York, 312 p. Smith, Oliver 0. and John Van Oosten. 1940. Tagging experiments with lake trout, whitefish, and other species of fish from Lake Michigan. Trans. Amer. Fish. Socl, 69:63-84. Smith, Stanford n. 1954. Method of producing plastic impressions of fish scales without using heat. Frog. Fish-Cult., 16(2): 75- 78. Smith, Stanford !. 1956. Life history of lake herring of Green Bay, Lake Michigan. 0.8. Fish and Wildlife Serv., Fishery 8u11., 57(109):87-138. Smith, Stanford 11. 1964. Status of the deepavater cisco population of Lake Michigan. Trans. Amer. Fish Soc., 93(2):155-163. Smith, Stanford R. 1968. Species succession and fishery exploita- tion in the Great Lakes. J. Fish. Res. Dd. Canada, 25(4):667- 693. ' Smith, Stanford 0., E.T. Buettuer, and Ralph Bile. 1961. Fishery statistical districts of the Great Lakes. Great Lakes Fish. Con. Tech. Rept. Mo. 2, 24 p. Van Oosten, John. 1929, Life history of the lake herring Leucicthzs artedi LeSueur) of Lake Huron as revealed by its scales, with a critique of the scale method. Bull. 0.8. Dureau of Fisheries , 44 (1928):265-428. Van Oosten, John and Paul 0. Es'chmeyer, 1956. Biology of young lake trout (Salvelinus namazcush) in Lake Michigan. 0.8. Fish and Wildl. Serv., Res. Rep. 42, 88 p. Wright, Kenneth J. 1968. Feeding habits of i-ature lake trout . (Salvelinus namazcush) in the Michigan waters of Lake Michigan. M. S. Thesis, Michigan State University, 42 p. HICHIGRN STQTE UNIV. LIBRRRIES 31293103161596