Kayden Nasworthy’s paper on the dark refuge for mysids was accepted last week in the Canadian Journal of Fisheries and Aquatic Sciences. He used uncrewed surface vessels – Saildrones – to collect hydroacoustic data in Lake Michigan and Lake Huron and analyzed that data for spatial distributions of mysid shrimps, an up to 25 mm long shrimplike crustacean that is common in the Great Lakes and Finger Lakes. This shrimp can represent up to 30% of the total zooplankton biomass in these lakes, and due to its large size, is a favorite food of many fish species. Therefore mysids migrate from at or near the lake bottom, where they seek refuge from fish predation in the dark during the day, to the water column only at night, as they feed on other zooplankton and phytoplankton that are more plentiful closer to the surface. But mysids have declined in some lakes, notably in Lake Michigan and Huron, and Nasworthy et al. show that the decline can be explained by the clearer water in these lakes which is associated with the increase in quagga mussels and decreased nutrient loading. Nasworthy et al.’s analysis of the spatial distribution of mysids using high coverage data from the Saildrones shows that the decline in Lake Michigan occurred in over bottom depths not deep enough to provide a dark refuge in the clearer lakes. By comparing with data from other Great Lakes, they also show that mysids declined only in lakes with reduced daytime refuge. These results will be further investigated in upcoming research from CBFS through Kayden’s PhD work.
Nasworthy, K.C., Watkins, J.M., Evans, T.M., Blair, H.B., Lawhun, S.D., Sethi, S.A., O’Brien, T.P., Warner, D.M., Pothoven, S., Scofield, A.E., Esselman, P.C., Rudstam, L.G., 2026. Availability of dark daytime habitat may limit mysid abundance in the Laurentian Great Lakes. Can. J. Fish. Aquat. Sci. in press.
