PHILADELPHIA — Scientists working with the Partnership for the Delaware Estuary and The Academy ofNatural Sciences have made an important discovery in the Delaware River between Chester, Pennsylvania, andTrenton, New Jersey: beds of freshwater mussels. This includes several uncommon species, two of which werepreviously believed to no longer exist in both Pennsylvania and New Jersey.
"Freshwater mussels are very sensitive to a variety of problems, including pollution, dams, water flows, loss offorests, and harvesting for their shells and as bait," said Dr. Danielle Kreeger, science director at the Partnershipfor the Delaware Estuary. "We have so few mussels left in almost all of our streams in the area, so to find sevenspecies living together in dense communities right near Philadelphia was unexpected and cause for celebration."
Freshwater mussels are the most imperiled of all plants and animals in North America Nearly three-quarters ofthe continent's 300 species are in decline, and many are either extinct or headed toward extinction. In theDelaware River Basin, most of the one dozen native species are classified as reduced, threatened, or locallyextinct. One of the basin's species is considered endangered at the federal level and others are listed asendangered at the state level. Water pollution and degraded habitats are the most common reasons for thesedeclines. That is why scientists are so excited to find them in this stretch of the river.
One reason freshwater mussels may be doing better in the Delaware River compared to surrounding tributariesis the fact that the Delaware is the longest free-flowing river east of the Mississippi. Dams often block fish fromswimming up the river, and this can interrupt the complicated breeding processes of freshwater mussels.Mussels rely upon fish to carry their babies, or larvae, around, including upstream. Whenever dams block thesefish, they fail to deliver their payload of mussel larvae to new areas where they can grow and thrive.Pennsylvania has more dams than any other state, and many of these are located in streams throughout theDelaware Valley. The lone exception is the Delaware River.
"Until this discovery, our surveys for freshwater mussels in southeastern Pennsylvania during the past 10 yearshave painted a grim picture. Only one species seems to still be prevalent in the area's streams, and even thatspecies is found in only a handful of locations anymore," said Roger Thomas, staff scientist at the Academy ofNatural Sciences' Patrick Center for Environmental Research in Philadelphia. These recently discovered bedsof mussels can be used to help support mussel reintroduction into other areas where they have been lost."
Dr. Kreeger and others are in the process of expanding a fledgling mussel-restoration effort with support from anumber of funders. These include ConocoPhillips, the National Fish and Wildlife Foundation, and thePennsylvania Coastal Resources Management Program. She believes it is now possible to increase musselpopulations throughout the Delaware River Basin by either breeding them in a hatchery or relocating adultsduring breeding season by releasing them in targeted streams. She and her colleagues at the Academy of NaturalSciences have been working with Cheyney University, the U.S. Fish and Wildlife Service, and the U.S.Geological Survey to experiment with different methods since 2007. They call their effort the FreshwaterMussel Recovery Program.
The Partnership for the Delaware Estuary is restoring mussels for many reasons, not just the fact that theseanimals are rare and endangered.
"Dense beds of mussels filter pollutants and make conditions better for fish and other aquatic life, improvingwater quality downstream in the estuary," said Jennifer Adkins, executive director of the Partnership for theDelaware Estuary. "We may have these beds of mussels to thank for keeping certain types of pollution, likenutrients, low in this part of the river. This helps make our waters more inviting for everyone."
Restoring freshwater mussels won't be easy or fast, however. Although freshwater mussels can help to boostwater quality, they are also some of the most sensitive animals to polluted water. Therefore, some area streamsmay not be able to sustain mussels until water quality is further improved or riverside woodlands are replanted.Also, freshwater mussels live to be up to 100 years old and are slow growing. But this does not concern Dr.Kreeger, who said, "We've made tremendous strides in improving some environmental conditions needed tosupport healthy ecosystems. That said, we know our job won't be complete until we see the return of theselong-lived sentinels of healthy waterways."
Of the seven species of native freshwater mussels discovered this past summer,
- Two species were thought to be extinct in Pennsylvania and New Jersey: the alewife floater, orAnodonta implicata, and the tidewater mucket, or Leptodea ochracea.
- Two species are considered critically-imperiled: the pond mussel, or Ligumia nasuta, and yellowlampmussel, or Lampsilis cariosa.
- Two species are considered vulnerable: the creeper, or Strophitus undulates, and the eastern floater, orPyganodon cataracta
- One species is listed as common: the eastern elliptio, or Elliptio complanata
Source: Academy of Natural Sciences