In 1991, an exotic bivalve called the zebra mussel moved into the Hudson River. Over the past two decades, the prolific species has colonized habitats with hard sediments, becoming the most abundant animal in the river's freshwater reaches. As competitors in the aquatic food chain, scientists have long speculated that zebra mussels may impact fish. A recent Canadian Journal of Fisheries and Aquatic Sciences article, written by Dr. David L. Strayer of the Institute of Ecosystem Studies (IES) and Drs. Kathryn A. Hattala and Andrew W. Kahnle of the NY State Department of Environmental Conservation (NYSDEC), has revealed that open-water fish species, like the commercially important American shad, are declining in response to the exotic invader.

Invasive species research is often limited by a lack of ecological data on pre-invasion conditions. Since the 1970s, utility companies on the Hudson River have gathered long-term data on juvenile fish populations as a condition of withdrawing cooling water from the river. These surveys began prior to the zebra mussel introduction, allowing for pre and post invasion assessment. Hudson River food web data has been collected by IES since the 1980s. Through analysis of this data, Strayer and colleagues have discovered that open-water fish, such as American shad and striped bass, have decreased in growth and abundance since the zebra mussel invasion. Conversely, species like sunfishes, which prefer vegetated shoreline habitat, have increased significantly.

Many of the open-water fish population declines were large and involved species of commercial or recreational importance, such as American shad and black bass. Strayer notes, "The changes we observed may lead to fewer adults of species such as American shad, and more adults of species such as redbreast sunfish in the Hudson. Maintaining a sustainable fishery for species like American shad, in the face of sharp population reductions, will be challenging. When a river
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Contact: Lori M. Quillen
quillenl@ecostudies.org
845-677-7600 x321
Institute of Ecosystem Studies
17-Aug-2004

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