Family: Unionid Mussels (Unionidae)
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The shad restoration program on the Connecticut River increased the range of A. implicata upstream about 125 miles (Smith 1985).
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In New York, alewife floaters are found in only the tidal Hudson River, and in the lower Delaware and Neversink Rivers, where it can be locally abundant. Historical records from elsewhere in New York appear to be misidentifications (Strayer and Jirka 1997). The species has been heavily impacted in the Hudson River estuary by the zebra mussel (Dreissena polymorpha) invasion.
Due primarily to the zebra mussel invasion, the population in the Hudson River estuary declined sharply (> 90%) from over 400 million individuals between 1991-1996 (Strayer and Smith 1996). Alewife floaters were recently rediscovered in 2000 in large numbers in the upper Delaware River system between Hancock and Port Jervis, including in the Neversink River tributary (Lellis 2001); this population appears more healthy, perhaps since zebra mussels have not yet invaded the Delaware River system. This rediscovery may represent a range expansion, possibly related to host fish (shad/alewife) distribution, since Strayer and Ralley (1991) found only one old dead shell in their extensive survey of the Delaware during the summer of 1990.