A Survey of Sport Fishing in the Illinois Portion of Lake Michigan March through September 1997

F-52-R12Report issued on: May 1998INHS Technical Report prepared for Illinois Department of Natural Resource

Mechanisms Affecting Recruitment of Yellow Perch in Lake Michigan

Report issued on: August 2001INHS Technical Report prepared for Great Lakes Fishery Trus

Potential Regulation of Age-0 Gizzard Shad by Hybrid Striped Bass in Ohio Reservoirs

Piscivores can control prey populations in north temperate lakes, leading to increased zooplankton and reduced phytoplankton. In reservoirs with gizzard shad Dorosoma cepedianum, an omnivorous planktivore, this cascade occurs with lower probability because while this fish is shorter than 60 mm in total length (TL) it readily consumes zooplankton but also switches to phytoplankton and detritus. Prospects for gizzard shad control probably hinge on piscivore consumption of age-0 individuals. Hence, we quantified capture efficiency of hybrids of striped bass Morone saxatilis × white bass M. chrysops (small: 190–250 mm, TL; large: 310–360 mm, TL) when combined with three gizzard shad size-groups (of five possible, ranging 40–120 mm) in a 500-L aquarium. Small hybrid striped bass selected 40-mm gizzard shad but preferred neither 60-mm nor 80-mm prey. Large hybrid striped bass demonstrated no selection for 40–120-mm gizzard shad. We incorporated these data into a bioenergetics model to evaluate whether hybrid striped bass could sufficiently reduce abundance of age-0 gizzard shad in Ohio reservoirs to permit increased zooplankton, thereby improving the potential for resident sport fish recruitment in reservoirs. Hybrid striped bass potentially increased larval sport fish occurrence only when they were stocked at high densities (≥350 fish/ha or ≥22 kg/ha) coupled with age-0 gizzard shad suffering low natural mortality and occurring at an intermediate peak density of 25 fish/m3 or less. We believe gizzard shad are largely immune to control by hybrid striped bass in Ohio reservoirs. Hence, managers must consider combining watershed management with predator stocking to regulate gizzard shad.This work was funded by Federal Aid in Sport Fish Restoration projects F-57-R and F-69-P, which were administered jointly by the U.S. Fish and Wildlife Service and the ODW, and by National Science Foundation grants DEB-9107173 and DEB-9407859 to R.A.S

Feeding Preferences of Omnivorous Gizzard Shad as Influenced by Fish Size and Zooplankton Density

In Ohio reservoirs, larval gizzard shad Dorosoma cepedianum less than 30 mm total length consume only zooplankton but frequently switch to detritus as they grow longer than 30 mm. However, in laboratory studies without detritus, gizzard shad longer than 30 mm consume crustacean zooplankton. To explore the composition of diets of omnivorous 30-100-mm gizzard shad, we completed 1-h laboratory feeding trials with different amounts of zooplankton and detritus and quantified the diets of gizzard shad in reservoirs. In both laboratory and field, gizzard shad ate primarily detritus but also ate zooplankton, consuming more as more became available, which demonstrates that this species is a facultative detritivore. In the field, zooplankton consumption declined as gizzard shad body size increased. We believe gizzard shad maximize growth by supplementing their low-protein detritus diet with more zooplankton as more becomes available. With this strategy, omnivorous gizzard shad may compromise the potential for food web manipulations based on the trophic cascade hypothesis in Ohio reservoirs.This work was supported by Federal Aid in Sport Fish Restoration project F-57-R, administered jointly by the U.S. Fish and Wildlife Service and the Ohio Division of Wildlife, to R.A.S

Linking Egg Thiamine and Fatty Acid Concentrations of Lake Michigan Lake Trout with Early Life Stage Mortality

The natural reproduction of lake trout Salvelinus namaycush in Lake Michigan is thought to be compromised by nutritional deficiency associated with inadequate levels of thiamine (vitamin B1) in their eggs. However, mortality driven by thiamine deficiency (commonly referred to as early mortality syndrome [EMS]) is not the only significant cause of low lake trout survival at early life stages. In this study, we sought to better understand the combined effects of variable levels of thiamine and fatty acids in lake trout eggs on prehatch, posthatch, and swim-up-stage mortality. We sampled the eggs of 29 lake trout females from southwestern Lake Michigan. The concentrations of free thiamine and its vitamers (e.g., thiamine monophosphate [TMP] and thiamine pyrophosphate [TPP]) as well as fatty acid profiles were determined in sampled eggs. Fertilized eggs and embryos were monitored through the advanced swim-up stage (1,000degree-days). Three distinct periods of mortality were identified: prehatch (0–400 degree-days), immediately posthatch (401–600 degree-days), and swim-up (601–1,000 degree-days). Stepwise multiple regression analysis revealed (1) that cis-7-hexadecenoic acid in both neutral lipids (NL) and phospholipids (PL) correlated with prehatch mortality, (2) that docosapentaenoic acid in PL and docosahexaenoic acid in NL correlated with posthatch mortality, and (3) that total lipids, TPP, and palmitoleic acid in NL, linoleic acid, and palmitic acid in PL correlated with the frequency of EMS. These results indicate the complexity of early life stage mortality in lake trout and suggest that inadequate levels of key fatty acids in eggs, along with variable thiamine content, contribute to the low survival of lake trout progeny in Lake Michigan