Jon Atwood, PhD
Department of Environmental Studies
The dwarf wedgemussel (Alasmidonta heterodon) is an endangered freshwater mussel (listed in 1990 under the Endangered Species Act) found in sparse populations along the Atlantic Slope from North Carolina to New Hampshire. Most of the information available for this species concentrates on distribution. Unfortunately little is known about habitat or environmental influences, though recent studies in New Hampshire, Massachusetts, and New York have contributed to our understanding of A. heterodon. This study documented some of the fundamental physical characteristics of sites where the USFWS has conducted mussel surveys on the Ashuelot River in southwest New Hampshire. The intent was to aid conservation planning strategies by detecting key factors that may play a role in Dwarf Wedgemussel presence or absence in sections of the river. Upon analysis, data collected in the fall of 2001 provided some evidence that water depth and substrate may be the physical factors which have the greatest effect on A. heterodon numbers and distribution. Sites with greater depth variation had a greater number of mussels, which may be a result of flow refuges (sheltered areas of the channel). Substrate particle size variation did not show a significant relationship with mussel counts, but the presence of boulders and large cobbles is important for maintaining stability of the channel bottom during high flows. The two upper most sites in the study area had the largest numbers of A. heterodon, though no conclusive evidence was found in this study to indicate the influence of a particular habitat characteristic on mussel presence or absence. Field observations indicate that the ability of a channel to dissipate energy either with large cobbles and boulders, or through side channels may be an important factor. This study served as a base from which to launch further studies of physical, biological, and chemical parameters that may affect dwarf wedgemussel distribution in the Ashuelot River.