Survey for the Newly Discovered Dan Spinymussel in the Dan, Mayo, and South Mayo Rivers, Virginia
Richard J. Neves
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Three spined, mussel species occur in the United States along the Atlantic slope: James spinymussel (Pleurobema collina), Tar spinymussel (Elliptio steinstansana), and Altamaha spinymussel (E. spinosa). The James spinymussel was listed as endangered in 1988 and was until recently considered to be endemic to the James River basin. Biologists with the North Carolina Department of Transportation discovered spinymussel populations in the Dan and Mayo rivers in North Carolina in 2000 and 2001, respectively. The U.S. Fish & Wildlife Service (USFWS) tentatively identified this species as Pleurobema collina. Two working hypotheses regarding the range of Pleurobema collina in the Dan River, North Carolina, have been proposed subsequent to more than 380 person-hours spent conducting surveys. The species was found in a 57-rkm reach of the Dan River and in a 19-rkm reach of the Mayo River, Stokes and Rockingham counties. The overall catch per unit effort (CPUE) varied from 0.08/hr to 1.48/hr. The purpose of this project was to determine where P. collina resides in Virginia and the extent of its range within the state. The USFWS requires surveys by the Virginia Department of Transportation for this species at all roadway projects on rivers and tributaries in Virginia until the range of this species is defined by adequate survey work. An informal preliminary survey design for P. collina was used during the summer of 2002 to improve the future survey design. Simple random sampling was deployed in surveys conducted in 2003 and 2004 to provide a good basis for comparison to gauge the efficiency of the informal sampling design used. In 2002, 116 person-hours were spent surveying 39 localities on the Mayo, Dan, and Smith rivers. The species was observed only in the South Fork of the Mayo River, Patrick and Henry counties, Virginia. During the summers of 2003 and 2004, 228 person-hours were spent surveying 38 equal-area river reaches (10, 000 m2) on the mainstems of the Dan, Smith, South Mayo, and Banister rivers. No specimens of P. collina (live or relic shells) were detected. However, two species, Elliptio complanata and Villosa constricta, were detected at almost every site surveyed. Water levels and flows were moderate to extremely high throughout the spring, summer, and early fall of both years, with water temperatures remaining low during the summer of 2003. A simple random sampling approach was designed to be easy, relatively quick, and cost-effective, applicable to most rivers, and to provide actual numbers for comparison. Negative results were reported after only 6 person-hours of searching within each randomly selected, equal-area river reach had been expended. P. collina was declared absent from the Virginia random sites surveyed in 2003 and 2004 with a confidence of approximately 90%. This information should eliminate the need to perform surveys for future work done in Dan and Mayo river basins.