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Dwarf Wedgemussel - August Species of the Month

What type of animal is sandwiched between two shells, has no backbone and no legs but one foot, a heart but no brain, teeth but no mouth, and gills but no lungs?

This describes the Dwarf Wedgemussel, a type of freshwater bivalve or mussel that resides in New Jersey. It was the August Species of the Month in honor of the 30th Anniversary of the New Jersey Endangered Species Conservation Act and the formation of DEP's Endangered and Nongame Species Program (ENSP).


There are 12 native freshwater mussel species in New Jersey, nine of which are listed as Endangered, Threatened or Special Concern. Often referred to as nature's vacuum cleaners, they improve water quality by straining particles and pollutants from water. They have a low tolerance for water-borne pollutants and are excellent indicators of water quality and stream health. The decline or extinction of New Jersey's freshwater mussels is being attributed to several factors, including pollution and development.

Since the early 1990s the DEP has conducted freshwater mussel surveys to locate and monitor existing populations. Survey information is now being used for recommending stream classification upgrades in critical, high quality habitats.

In order to recover healthy populations of the dwarf wedgemussel and other freshwater mussels, stronger management and clean up of the state's waterways is required, along with increased research and public understanding and involvement.

Dwarf wedgemussels in habitat
Dwarf wedgemussels on stream bottom
Photo courtesy of North Carolina Resources Commission

Dwarf wedgemussel habitat in the Pequest River


Dwarf wedgemussel habitat in the Paulins Kill
Photo courtesy of Allen Barlow


Putting "Mussel" into New Jersey's Wildlife Protection Effort

  • Freshwater mussels are among the most rapidly declining animal groups on the continent. The dwarf wedgemussel once existed in 70 locations within 15 major rivers draining into the Atlantic, from Canada to North Carolina. Today, the species exists in only 42 small sites within nine drainages. In New Jersey they are found only in sections of the Paulins Kill, the Pequest River, and a portion of the upper Delaware River

  • Primary threats to this species include water pollution from urban, industrial and agricultural run-off; erosion and sedimentation from construction and development; habitat loss from damming; dredging; and, exotic species of bivalves such as the Asiatic clam and zebra mussel.

  • The dwarf wedgemussel is protected through state and federal Endangered Species Acts, state and federal Clean Water Acts, rules related to flooding, and environmental reviews of proposed development projects.

  • Biologists conduct freshwater mussel surveys by visiting historic locations, suitable habitats and areas where host fishes are present. Viewing scopes and snorkeling gear are often used when searching rivers, streams and ponds, and shorelines are inspected for mussel shells. ENSP biologists also receive funding through the Division of Science, Research and Technology to survey for freshwater mussels as part of the Integrated Biological Aquatics Assessment Project (IBAA). The IBAA is a collaborative effort that focuses on collecting species and water quality information at existing DEP Ambient Biomonitoring Network (AMNET) sites.

  • Plans are under way to produce an atlas of New Jersey's freshwater mussels, which will include life history narratives, color plates of shells and maps.

Dwarf Wedgmussel – Facts of Interest

  • Freshwater mussels are filter feeders and eat by filtering plankton from water. By doing so, they slowly accumulate toxins within their bodies that were possibly in the water. They are known to be sensitive to potassium, zinc, copper and chlorine, as well as fertilizers and pesticides.

  • All freshwater mussels have a bivalve shell that is divided into a left and right half. It is made of calcium carbonate and the color and texture of the shell's outer surface is important for identification. The dwarf wedgemussel is known for its "humpbacked" shell that rarely exceeds one and a half inches long.

  • The dwarf wedgemussel is usually found in clear rivers, creeks, streams or ponds with slow to moderate current and having a muddy sand to sand and gravel bottom.

  • Mussels have a large, muscular foot that extends from between the shells and functions in locomotion (pulling it along) and anchorage (to the river bottom).

  • Certain species of fish are important to the dwarf wedgemussel. In mid-summer male mussels release sperm into the water while females downstream siphon the sperm and fertilize the eggs still stored in their bodies (gills). When the fertilized eggs are ready in spring they are released into the water and must attach to a specific host fish so that they can further develop. Eventually the young mussels will drop from the host fish to the streambed.

  • Young mussels are often eaten by ducks, herons and fishes while mature mussels can be eaten by raccoons and muskrat.

  • Although some freshwater mussels can live in excess of a century, the average life span of a dwarf wedgemussel is about 15 years.

Dwarf wedgemussels
Dwarf wedgemussels closed

Dwarf wedgemussels interior
Dwarf wedgemussels opened
Photos courtesy of
North Carolina Resources Commission

Ways You Can Help

  • Prevent soil erosion along waterways by planting and maintaining trees and other plants that act as buffers between the waterway and development and help keep soil in place, versus having it wash away.

  • Learn more about how water moves, what a watershed is, and how you can help prevent forms of water pollution often referred to as nonpoint source pollution. Visit the DEP Division of Watershed Management's Basic Watershed Information Web page.

  • It isn't too late to submit a grant proposal to DEP to help reduce water pollution! The deadline for submission is August 15 - activities can relate to education, demonstration projects, water monitoring and other efforts. To learn more, visit the DEP's website for nonpoint source pollution control grants.
Conserve Wildlife license plate
Order a Conserve Wildlife special interest license plate for your vehicle. It's tax-deductible, with 80% of the payment benefiting New Jersey's Endangered and Nongame Species Program.

Want to volunteer? Enjoy giving presentations? Looking for speakers? The Division of Fish and Wildlife offers two opportunities:The Endangered and Nongame Species Program's Speakers Bureau and the Division's Wildlife Conservation Corps. Visit these sites for details.

Want to learn new information quickly about New Jersey wildlife? The Division of Fish and Wildlife offers eight E-mail "mailing list" choices to the public. Visit the E-mail List Subscription Page to learn more about this free service and how to sign up.

Additional Sources of Information

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Department of Environmental Protection
P. O. Box 402
Trenton, NJ 08625-0402

Last Updated: October 7, 2004