Gastric evacuation rates, ration and consumption modeling of slimy sculpin (Cottus cognatus) and deepwater sculpin (Myoxocephalus thompsonii) from Lake Michigan

Understanding recruitment variation remains a key goal for fishery ecologists and managers.  A native planktivore in Lake Michigan, bloater (Coregonus hoyi) has exhibited dramatic recruitment variation over the past 37 years. We have undertaken a field, laboratory and modeling approach to determine whether benthic egg predation by slimy sculpins (Cottus cognatus), deepwater sculpins (Myoxocephalus thompsonii) and round gobies (Neogobius melanostomus) is driving this recruitment variability. Initial results of benthic egg predator diet analysis (N=500, collected January to May during the bloater spawning period) indicated that subpopulations of deepwater and slimy sculpin are consuming as much as 20% and 30% eggs by wet weight in the diet, respectively. Preliminary genetic analyses have revealed most eggs to be sculpin, rather than bloater. Initial gastric evacuation experiments have revealed that fish egg remains can persist in the stomach 8-10 days at temperatures of 4° C. More complete details on gastric evacuation are in progress for two prey types at 2 and 4° C for both sculpin species. Consumption modeling will synthesize diet data, gastric evacuation rates and population density to determine the proportion of the bloater egg production that is consumed by sculpins, and hence the relative impacts on bloater recruitment variability.