Mysis ecology in the Great Lakes

Jim Watkins, Lars Rudstam, Tom Evans, Hannah Blair, Kayden Nasworthy, Sarah Lawhun, Alex Koeberle, Toby Holda, Taylor Herne (Cornell), Brian O’Malley(USGS), Dave Warner (USGS), Steve Pothoven (NOAA-GLERL), Kelly Bowen (DFO Canada), Warren Currie (DFO), Rosaura Chapina and Jason Stockwell (University of Vermont), Alexander Karatayev and  Lyubov Burlakova (Buffalo State College). Funded by: US EPA GLNPO, USGS, and GLFC

Mysids are an important native species in all the Great Lakes as well as other inland lakes. Understanding mysid ecology is an essential component of understanding these systems as the species is both a major predator on zooplankton and a major prey for alewife, smelt and native coregonids. Historic declines in mysids, changing prey-fish communities, and oligotrophication in the Great Lakes have caused scientists to question the long-term reliability of mysids as a food source and to further investigate population dynamics and drivers of change. 

Continuing the findings of PhD student Toby Holda in his paper in 2023, we continued to combine monitoring data of EPA generated by CBFS with that of several other agency surveys now yielding an extensive time series from 1990 to 2024. Mysid abundance was added as a new sub-indicator in the State of the Great Lakes (SOGL) reporting cycle for 2025. 

Mysis abundance in lakes Ontario and Superior are currently highest and stable, while those of Lake Michigan have experienced a recent dramatic decline, and those of Lake Huron are low.  With the help of our Buffalo State collaborators, Lawhun is testing the use of day and night collected ponar dredge data to assess mysid use of benthic habitat in general and specifically the extent of partial diel migration with some component of the population not migrating off the benthos. With the help of Jacques Rinchard at SUNY Brockport, she also hopes to use fatty acid composition to distinguish these mysid populations and their use of plankton and benthic food sources. Nasworthy is using lakewide hydroacoustic data collected by the autonomous Saildrone to greatly expand traditional nighttime tow-based sampling for several Great Lakes. Kayden focuses on quantifying the nighttime mysid layer, and his first chapter to be submitted in 2025 provides a 2021 lake-wide assessment of mysids in lakes Michigan and Huron.  He has developed a hypothesis that mysids in several of the Great Lakes are now limited by the extent of dark daytime habitat in each lake that is shrinking due to increases in water clarity.  This change in light regime increases fish predation pressure on mysids.  The daytime data has also proved useful, providing a novel look at the timing and extent of mysid migration and their targeting by fish. Kayden is also finding that at great site depth mysids don’t migrate fully to the bottom during the day and are thus detectable by hydroacoustics. For the summer of 2023, the graduate students mentored undergraduate Rory Paltridge with field collections of mysids in deep Seneca Lake and shallower Keuka Lake.  Interestingly, mysids in shallow Keuka Lake were abundant at levels very  comparable to Seneca Lake, and both were at levels higher than all the Great Lakes.  Keuka Lake lacks extensive dark refuge, but with a recent Alewife crash has few fish predators that would target mysids. 

Our Great Lakes Fishery Commission grant to evaluate the decline of mysids in Lake Michigan is wrapping up with a final report in 2025. Kayden’s hydroacoustic survey of Lake Michigan in 2021 confirmed that mysids are still abundant in the northern deep basin.  However, mysid abundance is very low in shallower areas including the southern basin that once had abundant mysids.  This spatial pattern led to our hypothesis that mysids are limited by the extent of dark daytime refuge.  Over the decade of mysid decline we have seen populations of an important mysid predator Bloater increase.  Foodweb modeling by Hongyan Zhang predicted the opposite trend- that a mysid decline would lead to Bloater declines.  Sarah’s analysis of benthic sampling has confirmed that mysids caught in ponar surveys in 2015 and 2021 reflect the decline observed in the water column. Some mysids reside in the benthos at night; however the non-migrating component is a small proportion of the migrating population.