Methods matter: Gear and seasonal impacts on Lake Ontario prey fish biomass estimates

Session: Exploring Predator-Prey Dynamics and Feeding Ecology in the Great Lakes (2)

Brian Weidel, U.S. Geological Survey, Great Lakes Science Center, [email protected]
Michael Connerton, SUNY ESF, [email protected]
Jeremy Holden, OMNRF, [email protected]

Abstract

Prey fish surveys inform Lake Ontario Fish Community Objectives and species status but differing results among surveys can change our understanding of prey fish biomass dynamics. We contrast biomass indices for prey fishes from seasonally distinct bottom trawl surveys (April, June, October) as well as compare bottom trawl estimates to July-collected acoustic estimates. Comparing April to October biomass indices within the same year, April values were consistently higher for Alewife, Cisco, Lake Whitefish, Yellow Perch, Trout-perch. October trawl biomasses were greater than April surveys within the same year for Slimy Sculpin, Round Goby, and Johnny Darter. Biomass estimates for Rainbow Smelt and Lake Trout did not generally change across season. Differences in seasonal trawl catchability my result from spawning behaviors and changes in depth distributions. Acoustic and midwater trawl surveys often differed from bottom trawl surveys results. Cisco abundance based on July acoustics was substantially greater than any bottom trawl estimates.  In contrast, Alewife acoustic estimates were consistently lower than April-based Alewife estimates from the bottom trawl survey. We illustrate how differences among survey results could modify our understanding of Lake Ontario prey fish community dynamics, species status, and predator-prey balance.