The historical proliferation of hydroelectric dams across North America led to a loss in river system connectivity and alteration of habitat and flow regimes. Fish passage improvements are increasingly being examined as a means to reconnect river systems and restore remnant lake sturgeon (Acipenser fulvescens) populations. However, the recruitment benefits of passing adults above dams remains uncertain because limited information is available on the behavior and survival of juvenile lake sturgeon in hydroelectric reservoir systems. We conducted a four year study to assess the behavior, habitat use, movements, and route specific passage survival of juvenile lake sturgeon in two different sized reservoirs on the Black River in northern Michigan. Movements within the river system were tracked through the use of PIT-tag and acoustic telemetry monitoring technology. This involved surgically implanting transmitters within juvenile lake sturgeon to track individual movements. We developed an experiment to refine best surgical practices for this effort by evaluating the effects of incision placement (lateral vs. midline), closure method (suture vs. Vetbond), and tag burden on healing outcomes in age-0 lake sturgeon. Incision dehiscence was low for all treatments, except for midline incisions closed with Vetbond. Incisions closed with suture achieved better healing outcomes initially, but the healing process was 2-3 times more likely to relapse because of severe inflammation compared to lateral incisions closed with Vetbond, indicating that Vetbond is the preferred closure method when sutures are not able to be removed. During the field study, the majority of juveniles out-migrated from the reservoir system in less than 60 days and greater than 90% of movements occurred at night. However, 37% of the age-0 and 27% of the age-1 and age-2 lake sturgeon stayed in the reservoir systemfor more than 179 days. Also, age-0 lake sturgeon resided within the reservoir system and in the free flowing part of the river for longer periods of time compared with the older lake sturgeon. Outmigration numbers consistently peaked in the spring and fall months and were found to be related to temporal changes in water temperature and discharge levels. Habitat use was higher in areas with more silt habitat and less aquatic vegetation and in areas that had greater mean depth and max depth characteristics. At Kleber Dam the survival rates for passage through the vertical-shaft Kaplan turbine systems were estimated at 70.9% (SE = 0.093) for age-0 and 44.9% (SE = 0.138) for age-1 and age-2 lake sturgeon. At Tower Dam survival through the Leffel type-z vertical-shaft turbine systems was estimated at 86.9% (SE = 0.135) for age-0 and 59.9% (SE = 0.182) for age-1 and age-2 lake sturgeon. Passage survival through the Tower Dam Spillway was estimated at 100% (SE = 0.132) for age-0 and 100% (SE = 0.188) for age-1 and age-2 lake sturgeon. Impingement mortality at Tower Dam differed by age and was 0.4% for age-0, 13.3% for age-1, and 21.8% for age-2 lake sturgeon, while impingement mortality at Kleber Dam was not observed. Our results indicate that the majority of juvenile lake sturgeon will out-migrate rapidly from small reservoir systems in the fall and spring and that movements are nocturnal. However, our data also showed that juveniles can persist within small reservoirs for extended periods of time over multiple years and that reservoir morphology may limit entrainment. Turbine design, bar-rack spacing, and fish length and age at passage are key factors in determining levels of mortality and in forecasting recruitment benefits from lake sturgeon passage improvements. Our results also suggest that spillways can pass lake sturgeon with limited mortality, and operations at dams may be able to be modified to operate spillways at night during peak outmigration times to facilitate safer passage.
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