Exotic mussels expand deep into Lake Michigan while fish decline
Ann Arbor, MI — Biomass of non-native quagga and zebra mussels in Lake Michigan increased eight-fold between 2004 and 2007 after remaining relatively stable between 1999 and 2003. This recent dramatic increase was driven by expansion of quagga mussels into deeper depths (30 - 110 m or 98 to 361 feet ) of the lake since 2004.
USGS Great Lakes Science Center researchers have been recording biomass of zebra and quagga mussels in their annual lakewide bottom trawl survey that targets prey fish (alewife, bloater, smelt, sculpins) since 1999. Over this 9-year period, this survey has found the percentage of mussels in the total catch of fish and mussels to increase from 9% to 88%, meaning that only 12% of the total biomass in the trawl in 2007 was prey fish.
"The expansion and exponential increase of quagga mussels in Lake Michigan is clear," says David "Bo" Bunnell, Research Fish Biologist at USGS. "What remains debatable is whether the increase in mussels has directly led to the decline in prey fish. We concluded that the recent decline of prey fish in our survey was not the direct result of the mussels. Rather, the fish decline was likely due to other factors, such as shifts in fish habitat, poor fish recruitment that preceded the mussel expansion, or higher fish predation."
Original Publication Information
Results of this study, "Expansion of Dreissena into offshore waters of Lake Michigan and potential impacts on fish populations," are reported by David Bunnell, Charles Madenjian, Jeffrey Holuszko, Jean Adams, and John French in the latest issue (Volume 35, No. 1, pp. 74-80) of the Journal of Great Lakes Research, published by Elsevier, 2009.
Contacts
For more information about the study, contact Bo Bunnell, USGS Great Lakes Science Center, Ann Arbor, MI 48105, dbunnell@usgs.gov, (734) 214-9324.
For information about the Journal of Great Lakes Research, contact Marlene Evans, Editor, National Water Research Institute, 11 Innovation Boulevard, Saskatoon, SK, S7N 3H5, Canada; editor@iaglr.org; (608) 692-1076.
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