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Abstract
The zooplankton Mysis diluviana is a major component of the Laurentian Great Lakes food web and has recently declined in abundance in both lakes Michigan and Huron. Drivers of these declines are not well understood. Here, we explore the hypothesis that recent increases in water clarity have contributed to the decline of M. diluviana (mysids) by limiting the availability of daytime dark refuge from visual predators. Using Secchi depth data from 1996 to 2021, we estimate that dark refuge has decreased substantially in lakes Michigan and Huron where mysids have declined, but dark refuge has remained more stable in lakes Ontario and Superior where mysid populations did not decline. Results from a 2021 uncrewed surface vessel hydroacoustic survey and lake-wide, net-based sampling in lakes Michigan and Huron revealed significantly more mysids in areas with dark refuge, such as Lake Michigan’s northern basin. Conversely, Lake Huron contains sparse dark refuge consistent with low mysid densities in that lake. Higher water clarity leading to increased predation may be a primary driver of mysid declines in the Great Lakes.
Suggested Citation
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.A., Scofield, A.E., Esselman, P., and Rudstam, L.G., 2026, Availability of dark daytime refuge may limit mysid abundance in the Laurentian Great Lakes: Canadian Journal of Fisheries and Aquatic Sciences, 40 p., https://doi.org/10.1139/cjfas-2025-0217.
Study Area
| Publication type | Article |
|---|---|
| Publication Subtype | Journal Article |
| Title | Availability of dark daytime refuge may limit mysid abundance in the Laurentian Great Lakes |
| Series title | Canadian Journal of Fisheries and Aquatic Sciences |
| DOI | 10.1139/cjfas-2025-0217 |
| Edition | Online First |
| Publication Date | June 12, 2026 |
| Year Published | 2026 |
| Language | English |
| Publisher | Canadian Science Publishing |
| Contributing office(s) | Great Lakes Science Center |
| Description | 40 p. |
| Country | Canada, United States |
| Other Geospatial | Laurentian Great Lakes |