Bottom trawl assessment of Lake Ontario's benthic preyfish community, 2023

Since 1978, surveys of Lake Ontario preyfish communities have provided information on the status and trends of the benthic preyfish community related to Fish Community Objectives that includes understanding preyfish population dynamics and community diversity. Beginning in 2015, the benthic preyfish survey expanded from US-only to incorporate Canadian sites, increasing the survey’s spatial coverage to a lake-wide scale. Additionally, sampling in eastern US embayments (Black River, Chaumont, Guffin, and Henderson Bays), that were historically sampled during a September bottom trawl survey to index Yellow Perch (Perca flavescens; 1978–2007), resumed in 2015. The current survey provides abundance indices for sculpins, Round Goby (Neogobius melanostomus) and Bloater (Coregonus hoyi) with survey techniques, gear and timing comparable to Lake Michigan. This alignment provides a necessary biological reference point for measuring the success of Lake Ontario Bloater reintroduction. In 2023, the collaborative benthic preyfish survey completed 188 bottom trawl tows across main lake and embayment sites at depths from 6 to 249 m. In total, the 2023 survey sampled 85,801 fish from 38 species. Round Goby was the most common species comprising 43% of the total catch, followed by Deepwater Sculpin (Myoxocephalus thompsonii), and Alewife (Alosa pseudoharengus) at 22% and 13%, respectively. Slimy Sculpin (Cottus cognatus) lake-wide biomass density (0.06 kg/ha) remained low relative to historical observations from US waters during the 1980-1990s and was orders of magnitude lower in US than Canadian waters. Lake-wide Deepwater Sculpin biomass density remains high since the population recovery (4.1 kg/ha). Embayment catches continue to have unique species assemblages compared to main lake habitat. Historically common native benthic preyfish species like Trout-perch (Percopsis omiscomaycus), Spottail Shiner (Notropis hudsonius), and darters (Etheostoma spp.), that are now rare at main lake trawl sites, still occur in some embayment trawl sites.