Table 1. Endangered Juvenile Mussels Released in Tennessee and Virginia in 1998 - 2006

Species:

Oyster Mussel 288,949 Combshell 160,573 Tan Riffleshell 61,459 Purple Bean 25,290 Fanshell 11,918 Snuffbox 4,116 Cumberland bean 1,259 Dromedary 1,043 Little-wing pearlymussel 569 Birdwing pearlymussel 211 Cracking pearlymussel 5 Rough rabbitsfoot 150 Fluted kindneyshell 5,301

Total Released 560,843

PROPAGATION AND RESTORATION OF ENDANGERED MUSSELS (UNIONIDAE) AT THE PROPAGATION AND RESTORATION OF ENDANGERED MUSSELS (UNIONIDAE) AT THE FRESHWATER MOLLUSK CONSERVATION CENTER, VIRGINIA TECHFRESHWATER MOLLUSK CONSERVATION CENTER, VIRGINIA TECH

Richard J. Neves1, Dan Hua2, Jess W. Jones3, Rachel A. Mair4 and William F. Henley5. Virginia Cooperative Fish and Wildlife Research Unit, USGS-BRD, Department of Fisheries and Wildlife Sciences, Virginia Tech, Blacksburg, VA 24061, U.S.A. 1mussel@vt.edu; 2huad@vt.edu; 3jess_jones@fws.gov; 4rmair@vt.edu; 5whenley@vt.edu

*Literature cited is available upon request from the authors.

ABSTRACT

North America contains the greatest diversity of freshwater mussels in the world, approximately 300 species; however, this family of mollusks is the most imperiled taxon in the United States. Already, 35 species are presumed extinct and 70 species are listed as endangered or threatened. Without immediate efforts to recover federally protected species in watersheds throughout the country, the extinction of additional species is likely. Biologists at the Freshwater Mollusk Conservation Center at Virginia Tech have developed methods to produce and culture endangered juvenile mussels. The Tennessee Wildlife Resources Agency, U.S. Fish and Wildlife Service, Virginia Department of Game and Inland Fisheries, and Virginia Tech have entered into a cooperative program to fund the production, culture, and release of large numbers of endangered juvenile mussels into rivers in Tennessee and Virginia. The goal of this project is to augment natural reproduction at sites with these species and to release juvenile mussels at historic sites within rivers to expand population ranges. Between 1997 and 2006, nearly 560,000 juvenile mussels of 13 endangered mussel species were released into the Big South Fork Cumberland, Clinch, Powell and Hiwassee rivers. These rivers contain sufficient brood-stock and suitable habitat to augment and re-establish populations of rare mussels. Juvenile mussels are typically between 700-1200 m long and 60 days old at the time of their release into the rivers. Monitoring efforts at release sites have documented variable survival of juveniles. For example, survival of released juveniles of E. capsaeformis in the Clinch River has been documented, and augmentation efforts in the river appear successful. In contrast, released juveniles of the same species in the Powell River have shown no signs of survival. Propagation is now a viable tool to implement recovery of federally listed mussel species.

METHODS

The process of producing juvenile mussels begins by collecting suitable host fish from the river and holding them in captivity until gravid female mussels can be found. In the laboratory, the larvae (glochidia) in the gills of the female mussel are flushed out using a hypodermic needle filled with water. This non-lethal method allows us to return females to the river once her progeny have been removed. We have collected and transported female mussels of various species to our laboratory, removed their glochidia, and released them back to the site of capture. The following year we have then recaptured some of these female mussels and found them gravid again. The larvae can number more than 200,000 per female. These larvae are then introduced into a bucket holding the host fish, and aeration is used to keep the water agitated to allow larvae to attach to the gills of the fish. After 1 hour of exposure, the fish are moved to large aquaria where the attached larvae begin the transformation process, which requires 2-3 weeks. Aquarium systems are adapted to the flow and cover requirements of the specific host fishes. Glochidia are transformed at cool temperatures (19-22), which increases survival of host fish and allows glochidia to transform unharmed to the juvenile stage. Once these young juveniles drop from their host fish, they are collected by siphoning the tank bottoms. Newly metamorphosed juveniles are held in small containers with cultured algae and sediments for 1-2 weeks before release to the wild, or cultured long-term (2-6 months) in recirculating aquaculture stream systems. The culture process begins by placing newly metamorphosed juveniles in individual containers in the raceway of the recirculating aquaculture trough. The juveniles are cultured in dishes containing fine sediments. The culture unit is a 3 m long, 225 L plastic livestock feed trough. A 50:50 mixture of conditioned (dechlorinated) municipal water and well water is used in the culture system, with hardness ranging from 250 to 350 mg/L CaCO3. A 50 L square, plastic container serves as a sump reservoir, and PVC piping is used for delivery and return lines. Water is pumped through the raceway using a centrifuge or magnetic drive pump, and gravity-fed back to the sump reservoir through a standpipe. The juveniles are fed micro (5-10 m) algae, e.g., Neochloris oleoabundans, Nannochloropsis oculata, at a daily concentration of 20,000-30,000 cells/mL.

RESULTS & DISCUSSION

Long-term culture of juvenile mussels in recirculating aquaculture troughs is a feasible, cost-effective method to produce juveniles for population augmentation of endangered species, toxicity testing, or other research needs. For the best results, juveniles are cultured at temperatures ranging from 21-24C. Sustained temperatures > 27C seem to be detrimental to survival and growth of young juveniles in our recirculating aquaculture systems. Generally, survival of juvenile mussels is influenced by seasonal viability of newly metamorphosed juveniles, species differences, substrate composition, water quality, and predators. For example, the common rainbow mussel Villosa iris is much easier to culture than the endangered oyster mussel Epioblasma capsaeformis (p<0.05); additionally, the survival rate of transformed juveniles of both species is greater in the spring (p<0.05) than fall. Long-term (60-90 d) survival of endangered juveniles has ranged from 0-50%; however, techniques are now greatly improved and survival is expected to increase. Between 1998 and 2006, nearly 600,000 juvenile mussels of 13 endangered mussel species were released into the Big South Fork Cumberland, Clinch, Powell and Hiwassee rivers (Table 1). These juveniles are typically between 700-1200 m long, and 30-60 days old at the time of their release into the wild. Monitoring efforts at release sites have documented variable survival of juveniles. For example, survival of released juveniles of E. capsaeformis in the Clinch River has been documented, and augmentation efforts in the river appear successful. In contrast, released juveniles of the same species in the Powell River have shown no signs of survival presumably because of unsuitable environmental conditions. Propagation is now a viable tool to implement recovery of federally listed mussel species. The FMCC now averages approximately 100,000 juveniles of endangered species per year, for release into rivers of southwest Virginia, eastern Tennessee, and other locations specified in contracts.

INTRODUCTION North America contains the greatest diversity of freshwater mussels in the world, including nearly 300 species. However, this family (Unionidae) of mollusks is the most imperiled group of animals in the United States, with 213 species (72 %) listed as endangered, threatened, or of special concern (Williams et al. 1993; Neves 1999)*. Already, approximately 35 species are considered extinct, representing 12% of the North American mussel fauna disappearing in the last 100 years, a rate of extinction comparable to estimated faunal losses in tropical rainforests (Ricciardi and Rasmussen 1999). Most of the endangerment is caused by habitat loss or destruction due to impoundment, sedimentation, water pollution, dredging, coal mining, and other anthropogenic factors that affect the natural structure and function of free-flowing rivers (Neves et al. 1997; Neves 1999). The apparent correlation between coal mining activities and declines in mussel fauna in Appalachia likely continues to put many mussel species at risk of local extirpation or even extinction. Without immediate efforts to recover federally protected species in U.S. watersheds, the extinction of additional species is likely. To address the threat of future species losses, biologists at the Freshwater Mollusk Conservation Center (FMCC) at Virginia Polytechnic Institute in Blacksburg, Virginia, have developed the first techniques to propagate and culture endangered freshwater mussels for release of juveniles into rivers of the Tennessee River drainage. Propagation and culture of endangered mussel species has been recommended in recovery plans as a strategy to augment existing populations and to reintroduce species to sites within their historic ranges. The Tennessee Wildlife Resources Agency, U.S. Fish and Wildlife Service, Virginia Department of Game and Inland Fisheries and Virginia Tech University entered into a multi-year year cooperative program to produce, culture, and release juveniles of numerous endangered mussel species into tributaries of the Tennessee River drainage in Tennessee and Virginia. The goals of this project are to augment natural reproduction in extant populations, and to release juvenile mussels into historic habitat to expand the range of existing populations. The initial focus is the Clinch, Powell, Hiwassee and Big South Fork Cumberland rivers, where sufficient brood stock and suitable habitat exist to augment or re-establish populations of rare mussels. Because of high species richness and endemism in these rivers, these watersheds are of national significance for conservation of mussel resources in the United States. The selection of species and release sites (Figure 1) was determined by a joint meeting of mussel biologists representing the various funding and cooperating agencies. Life history of freshwater mussels Freshwater mussels are filter-feeders that have a unique life history, requiring that their larvae (glochidia) parasitize a fish host to complete their life cycle. Embryos mature into glochidia in the gills of the female mussel. Once mature, the female then releases the glochidia into the water, where they must attach and encyst on the gills, fins or epidermis of a suitable host fish for metamorphosis to the juvenile stage. Once this transformation is complete, juveniles excyst and drop off the fish host to begin their lives on the bottom of a river or lake. To maximize attachment of glochidia to host fish, some mussel species produce glochidia in packets (conglutinates) or have modified mantle-lures that closely resemble prey of fish, insect larvae and pupae, leeches, and even other fish, all of which seem to attract host fish to mussel glochidia (Figure 2). Depending on the species, mussel glochidia are brooded in the gills of females during either the winter (bradytictic) or summer (tachytictic). Winter brooders typically release their glochidia in spring and summer, while summer brooders release glochidia only in summer

RELEASE SITES

Clinch River:

• Horton Ford, TN

• Cedar Bluff, VA

Powell River:

• Bales Ford, TN

• McDowell Shoal, TN

North Fork Holston River:

• Cloud Ford, TN

Hiwassee River:

• Polk Co., TN

Cumberland River:

• Big South Fork National

Recreation Area, TN

Figure 1. Release sites of endangered juvenile mussels

in Tennessee and Virginia.

Release Site

Releasing Juvenile Mussels