Freshwater Mussels

Volunteer Survey Program

Scientific Studies

News & Reports

Freshwater Mussel Recovery Program

Freshwater Mussel Recovery Program

In 2007, the Partnership for the Delaware Estuary (PDE) launched the Freshwater Mussel Recovery Program which aims to conserve and restore native freshwater mussels in the Delaware Estuary. The mussel recovery program is part of PDE’s watershed-based shellfish restoration strategy which includes projects from headwaters to the Bay. Other example projects include: oyster reef restoration, marsh mussel living shorelines, and PDE’s 2011 marine shellfish priorities report.

Surveys

Surveys

PDE leads surveys of freshwater mussel populations throughout the Delaware Estuary watershed to fill vital data gaps. The last comprehensive survey of freshwater mussels in Pennsylvania, for example, was conducted prior to 1919. PDE conducts rapid surveys to find mussels over large areas and detailed surveys at specific sites to calculate the amount, sizes, and health of mussels. Water quality benefits provided by mussels can be estimated using information from these detailed surveys. Many partners have assisted PDE in mussel surveys in recent years, most notably the Academy of Natural Sciences of Drexel University. The Environmental Protection Agency and Philadelphia Water Department have also supplied essential support. We are also grateful to the state agency staff in Delaware, New Jersey and Pennsylvania for supplying PDE with data, helpful suggestions, and survey permits.

PDE and partners have made some startling discoveries over the years. Seven native species were found in healthy mussel beds along the Delaware River between Trenton and Philadelphia. Included were two species that had been believed to be locally extinct, and several other species found were state listed as rare, threatened or endangered. These finds offer hope that these species can eventually be reintroduced into streams from which they have been lost. A more rigorous scientific survey in 2012 revisited these discovered beds to learn more. For a summary of the current estuary-wide mussel status, click here.

Photo Credit Kathleen LaForce

Assessment

Assessment

One way PDE scientists help restore freshwater mussels is to compare and determine if specific streams are healthy enough for mussel restoration. This is accomplished by monitoring and comparing the health of mussels held in underwater cages at various restoration sites. Mussels used in these cages are taken from healthy beds in our reference streams and rivers. In streams where mussels continue grow and stay healthy, our scientists may determine that the stream can now support freshwater mussels.

This caging tactic was first devised in 2001 by Dr. Danielle Kreeger (Science Director, PDE) and Dr. Catherine Gatenby (currently at US Fish and Wildlilfe Service) when they were scientists with the Academy of Natural Sciences of Drexel University. Since then, it has been used to assess the effects of dam removal on mussel populations in Manatawny Creek, PA (2002) and the restroration readiness of Chester, West Branch Brandywine, White Clay Creeks in southeast PA (2007). See our reports page for more examples of these assessment studies.

Conservation

Conservation

Many of the native freshwater mussel populations in the Delaware River Basin appear to be in decline due to factors such as degraded or altered habitat, decreased water quality, decreased forested riverbanks, lack of suitable fish hosts, stormwater, dams, or altered water flow. PDE recognizes that every mussel is precious and it is vitally important that mussel populations that are stressed be identified and protected, especially in cases where federal or state-listed imperiled species are present. To protect these mussel beds, managers must be equipped with species-habitat maps to prioritize areas for conservation and consider possible designation of Critical Habitat for protection.

Reintroduction

Reintroduction

Reintroducing mussels to areas where they once thrived can be achieved with juvenile mussels from a hatchery (see #4 below), or by transplanting healthy adults. Many streams once contained mussels, but past disturbance wiped them out or dams blocked their fish hosts. Streams which could support mussels once again might need a little help to get going. This is where PDE and our partners assist by reintroducing baby mussels or adult mussels collected from healthy populations.

Since 2011, PDE scientists have successfully reintroduced mussels from healthy populations witin the Delaware River Basin to nearly one dozen streams and ponds that are being assessed for their ability to support mussels. Fixed with electronic tags, these mussels are periodically monitored to determine if they remain in the reintroduction area. Additionally, scientisits measure shell lengths of mussels to find out how well the mussels grow in different waterways!

Propagation

Propagation

Propagation is where juvenile mussels are spawned using their host fish in a mussel hatchery. In order to do this, female mussels that have already fertilized their eggs are colleted from healthy populations and put into hatchery tanks with host fish. When females release their young, fish become “infested” with larvae that attached to their gills for a period of several weeks (they don’t harm the fish at moderate levels of infestation.) After mussel larvae transform (metamorphose), they drop off the fish and begin their life as juvenile mussels. PDE has had success working with Cheyney University, the U.S. Fish and Wildlife Service, U.S. Geological Survey and the Academy of Natural Sciences of Drexel University to develop and refine tactics to propagation species native to the Delaware River Basin. Future efforts are aimed to work with even more partners such as the Philadelphia Water Department’s Fairmount Water Works to develop a hatchery in Philadelphia.

Habitat Restoration

The habitat requirements of freshwater mussels vary by species; however, some universal needs are stream bottom stability, adequate water flow, as well as contaminant-free waters. Streams and rivers that are subject to flashy flows (e.g. severe flooding), unstable stream bottoms, low water levels, and high amounts of contaminants will be unable to support healthy mussel populations. This presents an opportunity to expand the carrying capacity for native mussels by enhancing habitat and water quality conditions. For example, PDE is working to design living shorelines that include suitable substrates for mussels within a coastal “habitat mosaic.” Projects that stabilize streambanks, stabilize stream bottoms, remove dams, restore forests along streamsides, and restore underwater vegetation also benefit mussels. Since mussels can also be killed or stressed by certain contaminants (e.g. copper, aluminum, and ammonium), efforts to detoxify the water and stream bottom are also included here. PDE intends work with partners to define Habitat Suitability Indices and other metrics to help guide habitat-associated restoration (and mitigation).

Research & Monitoring

Research & Monitoring

Currently, there are important data that we need to gather which will help advance mussel recovery efforts and enhance our ability to link restoration to measureable outcomes and goals of managers. A better understanding is needed for the life history, physiological ecology, and carrying capacity for our local mussel species. Life history information includes knowledge of suitable fish hosts to support mussel reproduction (different mussel species depend on specific fish) and link to fish passage and management concerns. Physiological data are needed to develop predictive models of beneficial water quality outcomes, understand species habitat requirements, and water quality needs, nutritional demands, and mutually beneficial relationships between mussels and other biota such as submerged aquatic vegetation. Population- and ecosystem-level studies are needed to develop predictive models of maximal current and future sustainable densities (i.e., how many mussels can a stream support?) Monitoring of previous restoration activities will be required to assess outcomes and facilitate adaptive management of mussel restoration in the Delaware Estuary.

Partner Coordination

As a tri-state National Estuary Program, PDE has been working to launch and coordinate freshwater mussel restoration among diverse sectors within the Delaware Estuary watershed. To date, core partners have included state heritage and environmental programs for Delaware, New Jersey and Pennsylvania, federal representatives at U.S. Fish and Wildlife Service, academic and nonprofit research institutions (Academy of Natural Sciences of Drexel University, Cheyney University, Rutgers University), companies (e.g., Cardno-ENTRIX) and water suppliers (e.g. Philadelphia Water Department, United Water). PDE intends to soon form a technical advisory workgroup affiliated with the Science and Technical Advisory Committee to bring together and expand participation and provide technical peer review for freshwater mussel restoration. Formation of this group will also facilitate interstate cooperation and link to national conservation priorities.