Environmental Review Toolkit
Water, Wetlands, and Wildlife


(Glenn R. Nelson II)

Pennsylvania Department of Transportation

Surveying Freshwater Mussels in Pennsylvania

Pennsylvania's Allegheny River Basin is the nation's "last stronghold" for two federal ESA-listed (endangered), freshwater mussels: the northern riffleshell and the clubshell. Countless numbers of these mussels are thriving in the clean waters of the upper Allegheny--a sharp contrast to rivers elsewhere where the species formerly existed and where they have either disappeared or live in low numbers.

In the mid-1990s, when the Pennsylvania Department of Transportation (PennDOT) needed to replace several bridges in the upper Allegheny, little was known about the densities of endangered mussels. The recovery plan for these species identified the presence of low numbers and a sporadic distribution throughout the 66-mile river reach. One mussel survey on a bridge-replacement project clearly identified greater densities of mussels, so PennDOT partnered with the U.S. Geological Survey (USGS) Biological Resources Division, to conduct multi-year qualitative and quantitative mussel studies on Pennsylvania's Upper Allegheny. The studies would determine mussel densities, improve the scientific data used in Endangered Species Act consultations, and identify potential conservation and recovery measures.

In the qualitative surveys, USGS divers and snorkelers surveyed approximately 60 200-meter sites with 12 substrate transects each, identifying all the mussel species they found and recording their findings on water-adaptable armbands. Both high mussel-density sites and sites with low densities were surveyed quantitatively. In these surveys, the USGS scientists counted, measured, and identified the freshwater mussels they encountered. They also recorded the size and type of mussel bed habitat.

So far, 56 sites have been surveyed qualitatively and 19 sites quantitatively. In the first river section (about 40 river-miles), the surveys identified 24 freshwater mussel species in thick densities-an estimated 28 million individual common mussels plus more than 7 million northern riffleshell and at least 1 million clubshell. In surveys on the second, 25-mile river section, results point to estimated mussel numbers far exceeding those of the first river section. These results will be the basis for future decision making between PennDOT and the U.S. Fish and Wildlife Service (USFWS).

Several mussel relocations associated with bridge projects on the Allegheny have been completed and mussels have been successfully relocated. What's more, the USGS Water Resources Division is conducting hydraulic studies using acoustic technologies to create predictive models for freshwater mussel habitat. These technologies are also being used to study the impacts of bridge removal and replacement, to monitor modifications to the river bed, and to find ways to further minimize impacts to freshwater mussels and their habitats.

Perhaps most promising for the recovery of the northern riffleshell and clubshell is a future bridge-replacement project located in an area of the river with high densities of these two species. PennDOT and its partners are discussing how they might relocate mussels from this location to other rivers where the species are found only in low numbers. Also promising are ongoing research studies at the White Sulphur Springs National Fish Hatchery, where the USFWS Ohio River Islands Dive Team salvaged and held a number of mussels. If the captive-care-and-propagation studies succeed, PennDOT will be able to donate freshwater mussels identified as "take" for a bridge replacement to other locations in the animals' historic range. A far-reaching ecosystem benefit indeed!

For more information, contact Toni Zawisa, azawisa@state.pa.us

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