Balancing Fisheries Management and Water Uses for Impounded River Systems

Assessing Fish Biomass and Prey Availability in Ohio Reservoirs

R. Scott Hale, Donald J. Degan, William H. Renwick, Michael J. Vanni, and Roy A. Stein

doi: https://doi.org/10.47886/9781934874066.ch34

Abstract.—In Ohio reservoirs, a perceived excess of available gizzard shad Dorosoma cepedianum prey and poor recruitment of stocked walleyes Sander vitreus during the 1970s resulted in research to develop and expand a program to stock saugeyes (walleye × sauger S. canadensis), a hybrid better suited for shallow, productive, and turbid reservoirs with short water-residence times. Development of successful production techniques increased saugeye stocking from fewer than 1.2 million to 6–10 million fingerlings (28–42 mm) per year during 1980 through 1990, presenting the challenge of determining stocking rates suited to available prey. To improve Sander spp. stocking practices, we assessed prey supply by quantifying fish biomass in Ohio reservoirs using acoustic technology. Fish biomass varied from 10 to 897 kg/ha as estimated by 53 acoustic surveys conducted on 16 reservoirs during 1999–2006. Among 15 variables associated with reservoir productivity, 84% of the variability in fish biomass was explained by watershed area, trophic state, reservoir area, and reservoir volume; watershed area plus trophic state explained 77% of this variability. Dominance of fish prey smaller than 150 mm, which represented more than 80% of fishes sampled in acoustic surveys, revealed that reservoir fish biomass largely reflected the upper limit of prey fish biomass morphologically available to age-1 and older Sander spp. Gizzard shad represented more than 50% of the fishes captured in 92% of gill-netting surveys conducted in conjunction with acoustic surveys. Unexpectedly, reservoirs with extensive prey biomass occasionally had poor recruitment for Sander spp., and these reservoirs often were stocked at lower rates than ones with better recruitment. Fisheries managers in Ohio can improve stocking practices by using acoustic surveys to predict reservoir capacity for stocked sport fish based on reservoir attributes, then applying these results to details of reservoir-specific recruitment of stocked fishes and their consumptive demand. Refining this supply and demand approach will require continual progress in understanding reservoir ecosystems and their watersheds.