Status and trends of the Lake Huron prey fish community, 1976-2024

The U. S. Geological Survey-Great Lakes Science Center has monitored annual changes in the offshore (depth > 9m) prey fish community of Lake Huron since 1973. Monitoring of prey fish populations in Lake Huron is based on a bottom trawl survey that targets demersal species (i.e., those predominantly or intermittently associated with the lake bottom) and an acoustic-midwater trawl survey that targets pelagic species and life stages. Prey fish abundance and species composition in 2024 was generally consistent with trends observed over the past decade. Bloater (Coregonus hoyi) remains the most abundant and widespread prey species, although its abundance is starting to decline owing to changes in demographic factors that are interacting to suppress reproduction. Rainbow Smelt (Osmerus mordax) remain widely distributed across Lake Huron but their dynamics vary by basin. Rainbow Smelt populations currently are larger in Georgian Bay and the North Channel than in the main basin where they have produced eight weak year classes over the past decade including in 2024. Populations of Alewife (Alosa pseudoharengus) continue to be comprised of low numbers of age-0 individuals, and sculpin communities consist primarily of Deepwater Sculpin (Myoxocephalus thompsonii) due to the reduced abundance and distribution of Slimy Sculpin (Cottus cognatus). In contrast, biomass of the invasive Round Goby (Neogobius melanostomus) in 2024 was the highest observed in the bottom trawl time series and was over four times greater than in 2023. Overall status of main basin prey fish community was rated as ‘fair.’ Stable dynamics of main basin Bloater populations and evidence of continued recovery by Cisco (Coregonus artedi) in the North Channel were interpreted as positive community trends, whereas growth and expansion of Round Goby populations and low species diversity of pelagic prey fish communities are inconsistent with fish community objectives. Use of complementary surveys (bottom trawl, acoustics) remains useful for evaluating prey fish status in Lake Huron, where prey fish community dynamics vary by basin and prey fish responses to changing environmental conditions depend on species and/or habitat.