Freshwater Mussel Restoration

 

 

About the Freshwater Mussel Recovery Program:

In 2007, the Partnership for the Delaware Estuary (PDE) launched the Freshwater Mussel Recovery Program (FMRP). The goal of this initiative is to foster greater conservation and restoration of native species of freshwater mussels in the Delaware Estuary watershed and larger Mid-Atlantic region.

There are two main reasons to protect and restore mussel beds in our streams, rivers and lakes. First, freshwater mussels are the most imperiled of all animals and plants both locally and across the United States. Second, healthy beds of mussels furnish many important benefits, such as cleaner water and better habitat for fish and wildlife.

About a dozen species of native freshwater mussels (family Unionidae) once thrived throughout the Delaware River Basin. Today, only two species can be easily found and even those are greatly reduced in numbers and range. Most streams and rivers have no mussels at all and when found they often are comprised of only old animals that do not appear to be reproducing successfully. Since each adult mussel filters gallons of water every day, healthy streams with thousands (up to millions) of mussels per mile can be help sustain good water quality, and when the mussels are lost from streams we believe this contributes to degraded water quality.

The Freshwater Mussel Recovery Program is a key component in PDE's watershed-based shellfish restoration strategy which includes bivalve conservation, enhancement and restoration projects from headwater streams to the mouth of Delaware Bay. Other example projects in the watershed shellfish strategy include oyster reef restoration and marsh mussel living shorelines. By reintroducing native species of freshwater mussels, and at the same time, boosting current populations, PDE will improve the ecosystem in the following ways:

  • refilling open niches in the food web
  • providing ecosystem services, or tangible benefits like improved water quality and habitat complexity
  • intercepting and filtering out pollutants before they reach the tidal estuary
  • reassuring the public that ecosystems are indeed being improved
  • preserving imperiled species

The Freshwater Mussel Recovery Program seeks to restore the population, diversity, and resilience of native mussels through a mix of conservation, expansion, and reintroduction tactis, summarized in the diagram below. Each of our five main activity areas is described below:

Surveys

Restoration Suitability Tests

Reintroductions

Propagation

Education and Outreach

 

1. Surveys


PDE leads surveys of freshwater mussel populations throughout the Delaware Estuary watershed whenever and whereever possible because our existing data for the distribution and abundance of native species is insufficient to track status and trends and to prioritize conservation and restoration efforts. The last comprehensive survey of freshwater mussels in Pennsylvania, for example, was conducted prior to 1919. In recent decades, each of the three states (DE, NJ, PA) maintain a heritage database for species presence and absence data, but these data are not readily available and they are insufficient for setting conservation priorities in many areas.

Mussels surveys for presence/absence are referred to as "qualitative" searches that yield important information about the distribution of mussels, compared to past conditions. They are useful for raid assessment of large areas. Mussel surveys for abundance and size classes are "quantitative" searches that yield information on the population health which can also be used to estimate water and habitat quality benefits. Quantitative mussel surveys are rigorous and usually are only conducted over limited areas. PDE maintains a two-tier framework for its mussel surveys that uses qualitative searches to efficiently cover large areas, and then when possible quantitative surveys are conducted strategically in areas with healthy mussel beds, which serve as reference sites for basing our restoration efforts.

Many partners have assisted PDE in mussel surveys in recent years, most notably the Academy of Natural Sciences. The Environmental Protection Agency and Philadelphia Water Department have also supplied essential in kind support. We are also grateful to the state agency staff in Delaware, New Jersey and Pennsylvania for supplying PDE with data, helpful suggestions, and permits for our survey efforts.

Mussel surveys in streams of the Delaware Estuary watershed between 1999 and 2010 yielded very little finds. For example, only about 5 of >70 streams in southeast PA had any mussels at all. In the early 20th century, most of these same streams had 4-7 species in abundance. This dramatic decline is indicative of degrading conditions over the 100 years of available data. Unfortunately, the decline of our area's mussel assemblage appears to be declining despite vast eforts to reverse declines in environmental conditions since the 1970's. For example, in 1999-2000 PDE staff found live individuals of two mussel species in White Clay Creek, PA, but none have been spotted since then despite repeated surveys.

In contrast to the degraded mussel assmebalges in the area's streams, conditions appear stable in the tidal freshwater portion of the Delaware Estuary where PDE and partners made some startling discoveries over the past few years. Approximately seven native species were found living together in apparently healthy beds along the Delaware River between Trenton and Philadelphia. Include were two species that had been believed to be locally extinct, and several other species are 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 rigourous scientific survey is planned in 2012 in this area to determine the importance of these discovered beds for water and habitat quality and to gauge if they are robust enough to be used for reintroduction and propagation efforts.

2. Restoration Suitability Tests


There are so many streams without mussels, and funding and resources for mussel restoration are limited. Therefore, we need to carefully select streams for restoration to maximize resturns on our restoration investments because in some cases current conditions may not support the reintroduction of mussels, such as if the water or food conditions are still inadequate.

This is why a key early step in the Freshwater Mussel Recovery Program is to compare candidtate restoration streams for their "restoration readiness." The PDE team does this by monitoring and comparing the health of mussels held in underwater cages at various prospective restoration sites. Mussels used in these cages are taken from healthy beds in our reference streams and rivers. In streams where these "caged sentinels" show good health after one year in comparison to the source streams, we prioritize the new streams as ready for mussel restoration. However, if mussels die or lose fitness, that waterway will not be targeted.

This caging tactic was first devised in 2001 by Dr. Danielle Kreeger (currently at PDE) and Dr. Catherine Gatenby (currently at USFWS) when they were scientists with the Academy of Natural Sciences. 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). Starting in May 2011, PDE launched a restoration readiness caging study in Darby and Crum Creeks in PA. The current study is expected to last until spring 2012.

3. Reintroductions


Reintroduction can be achieved by seeding streams with juvenile mussels from a hatchery (see #4 below), as well as transplanting healthy adults that are reproductively active. Many streams and rivers in the Delaware River Basin no longer have any mussels whatsoever, and reasons for this are manyfold.

In some cases, some past disturbance event could have wiped the mussels out and their natural recolonization is blocked by dams that impede movements of fish which serve as hosts for mussel larvae (mussels naturally disperse via this mechanism). In these cases, the current water quality and growing conditions might be fine to sustain mussels, but they simply need a helping hand getting back into the area. This is where PDE and our partners lend an assist by transplanting either baby mussels that we produce or adult mussels that we relocate from healthy populations.

In 2011, we undertook our first major reintroduction with adult mussels. On June 16th, 100 eastern floaters (Pyganodon cataracta) and 100 eastern elliptios (Elliptio complanata) were collected from the Delaware River from the area around Tacony-Palmyra Bridge. Each mussel was tagged with a uniquely numbered plastic tag as well as with a PIT (passive induction transponder) tag. The size of each mussel was recorded. Approximately 30 E. complanata were also collected from Ridley Creek, which harbors one of the last healthy populations of this species in southeast PA. These 230 mussels were then relocated to 6 reaches, three in Chester Creek and three in Ridley Creek. Over time, we will monitor the location and survivorship of the different species and source populations of mussels which were relocated to six new homes. The information we get should tell us whether mussel reintroduction can be succesful and whether local conditions or mussel species affects this success.

This 2011 reintroduction test marks probably the first time that Chester Creek has had any mussels in decades. It also is probably the first time that either stream has had P. cataracta in perhaps 100 years. Initial surveys for electronic tagged mussels in both Chester and Ridley Creeks showed high survivorship, even after Hurricane Irene and Tropical Storm Lee hit. The storms did appear to move some of the mussel beds, and in one location animals had been largely buried by a new sand bar. But all sites still had at least some live mussels after the storms, and in about half the locations we found many mussels had not moved at all. The new electronic tag system is working well and will greatly improve PDE reintroduction and mark-recapture studies with freshwater mussels.

4. Propagation

Broodstock mussels are collected from healthy natural beds at a time of year when females are actively brooding larvae. Suitable fish hosts are also collected at this time, and mussels and fish hosts are then cultured together in a hatchery whereby 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.

Although we have know how to spawn and grow marine species such as oysters for more than 100 years, it is only in the past 10-20 years that techniques have been developed to mimic natural processes and obtain juvenile mussels in hatcheries. Hence, there is still considerable R&D needed to discern exact fish host-mussel relationships, dietary and rearing needs of baby mussels, and to optimize and enhance the predictability of mussel propagation. Nevertheless, we have had success working with Cheyney University, the U.S. Fish and Wildlife Service, U.S. Geological Survey and Academy of Natural Sciences to develop and refine tactics to propagation species native to the Delaware River Basin.

In 2009 we had our first successful propagation event for eastern elliptio mussels, which were produced using American eels and lake trout as fish hosts. In 2010, natural mussel populations did not become gravid enough to sustain propagation, which could have been associated with the severe winter of 2009-2010 followed by too rapid of a spring warmup. In 2011, we were on track to have a banner year for production of juvenile mussels, but the effort was aburptly halted by climate control problems at the hatchery. Future efforts will depend on securing new funding.

5. Education and Outreach


PDE works to educate the public about freshwater mussels and the Freshwater Mussel Recovery Project though public presentations and speaking engagements, newsletter articles, providing information through this website, and presentations at regional and national conferences.  With some new funding, we intend to strengthen these efforts over the next few years by engaing the public via a new community-based volunteer survey program. We will be working with selected watershed groups to train volunteers how to conduct basic mussel surveys and then upload data to a PDE portal, which scientists can then use to structure future fieldwork and conduct scientific assessments more efficiently. A web-based field guide to the mussels of the Delaware River Basin and a mussel sruvey guide for the public will also be produced in 2012. Additional new concepts for outreach include "mussel gardening" of either relocated animals or hatchery-produced juvenile "seed" mussels.

 

 

     

Dr. Danielle Kreeger (right) guides members of the Partnership for the Delaware Estuary's staff and various committees on a tour of a Brandywine River survey site following a meeting in July of 2008.

 The Partnership for the Delaware Estuary is studying whether or not freshwater mussels, like these Elliptio complanata specimens, can flourish once again in the rivers of southeastern Pennsylvania. If so, they will help clean local waters

 

Freshwater Mussel Background

Similar to other regions of the United States, freshwater mussels in the Delaware Estuary's watershed are the most imperiled of all plants and animals. All but a few of our 12+ native species are in danger of being wiped out. In fact, even the most common species are disappearing in many streams. This could be the result of a failure to reproduce, an inability to exchange genes among neighbors, or the deterioration of habitat. Whatever the reason for their decline, this spells trouble.

Freshwater mussels have a complicated life cycle, whereby fish hosts are needed for their larvae to be able to metamorphosis into juvenile mussels. Usually, specific sizes and species of fish are needed for this purpose, and so any disturbance to the particular fish assemblage that mussel rely on can short-circuit the reproductive cycle of mussels. This is why dams that block fish passage are so harmful to freshwater mussels.

Another interesting feature of freshwater mussels is their slow growth rates and long lifespans, often to 80-100 years. Unlike marine species of bivalves that can grow to adulthood in 2 years or less, freshwater mussels don't even reach spawning age until 8-10 years. Hence, when freshwater mussels are impacted by disturbance, they cannot recover quickly.

Finally, as filter-feeding animals that must pump large quantities of water across soft tissues in order to feed and breathe, freshwater mussels are exposed to contaminants moreso than animals that feed on larger sized foods. They can be very sensitive to a variety of pollutants. For all of these reasons, the health of freshwater mussel populations is one of the best indicators of overall water and habitat quality in America's freshwater systems. To have the healthiest mussel assemblages, a stream needs to have good riparian coverage (wooded corridors), free flowing waters (no dams), good water quality, adequate water quantity (good base flow), and healthy native fish populations. PDE has therefore elevated freshwater mussel restoration as a top target for overall restoration of the Delaware Estuary watershed.

Restoration of mussel beds would not just serve as an indicator of envirionmental improvement for the watershed - rather, it would promote positive feedbacks that reinforce efforts to boost water and habitat quality. This is because freshwater mussels filter water, enrich the food supply, stabilize riverbeds, and enhance habitat.

Future Plans

Not many know about the wonderful world of freshwater mussels and the many benefits that can be obtained by conserving and restoring them. PDE intends to expand its outreach efforts to boost basic knowledge and to promote FMRP activities. We aim to work as hard and fast as possible to save what is level of the natural mussel assemblage and restore the assemblage across the Delaware Estuary watershed. We also hope to team up with scientists, managers and outreach groups in adjoining watersheds such as the Cheasapeake Bay because most of the same issues and species are shared. Funding is diffult to obtain for this poorly known resource, and so the relative balance of FMRP activities will necesssarily fluctuate from year to year based on resources at PDE and our many partners. We welcome any interested scientists, managers, and watershed groups to work with us to expand these efforts.

Acknowledgements

The Freshwater Mussel Recovery Program has been made possible thanks to cooperation with the Academy of Natural Sciences of Philadelphia, Cheyney University, Drexel University, U.S. Fish and Wildlife Service and the U.S. Geological Survey. Financial support has been provided by ConocoPhillips, the National Fish and Wildlife Foundation, the DuPont Clear into the Future program, and Pennsylvania Coastal Zone Program.

If you are interested in learning more about the FMRP initiative, please contact either Danielle Kreeger or

Angela Padeletti at (800) 445-4935.