Genetic management guidelines for captive propagation of freshwater mussels

Journal of Shellfisheries Research, August, 2006 by Jess W. Jones, Eric M. Hallerman, Richard J. Neves

ABSTRACT Although the greatest global diversity of freshwater mussels (~300 species) resides in the United States, the superfamily Unionoidea is also the most imperiled taxon of animals in the nation. Thirty-five species are considered extinct, 70 species are listed as endangered or threatened, and approximately 100 more are species of conservation concern. To prevent additional species losses, biologists have developed methods for propagating juvenile mussels for release into the wild to restore or augment populations. Since 1997, mussel propagation facilities in the United States have released over 1 million juveniles of more than a dozen imperiled species, and survival of these juveniles in the wild has been documented. With the expectation of continued growth of these programs, agencies and facilities involved with mussel propagation must seriously consider the genetic implications of releasing captive-reared progeny. We propose 10 guidelines to help maintain the genetic resources of cultured and wild populations. Preservation of genetic diversity will require robust genetic analysis of source populations to define conservation units for valid species, subspecies, and unique populations. Hatchery protocols must be implemented that minimize risks of artificial selection and other genetic hazards affecting adaptive traits of progeny subsequently released to the wild. We advocate a pragmatic, adaptive approach to species recovery that incorporates the principles of conservation genetics into breeding programs, and prioritizes the immediate demographic needs of critically endangered mussel species.

KEY WORDS: freshwater mussels, genetic guidelines, conservation units, artificial propagation, imperiled species.

INTRODUCTION

North America contains the greatest diversity of freshwater mussels in the world, approximately 300 species. However, the superfamily Unionoidea is the most imperiled group of animals in the United States, with 213 species (72%) considered endangered, threatened, or of special concern (Williams et al. 1993, Neves 1999). Already, approximately 35 species, or 12% of the North American mussel fauna, have become extinct in the last 100 y (Neves et al. 1997), an extinction rate comparable to estimated faunal losses in tropical rainforests (Ricciardi & Rasmussen 1999). For example, the Tennessee River basin historically was home to 102 species of mussels, and hence is the putative center of mussel diversity in North America (Parmalee & Bogan 1998). Of those original 102 species, 12 are extinct, 26 are listed as endangered under the Endangered Species Act, 20 are extirpated from the basin, and only about 30 species have stable populations (Parmalee & Bogan 1998). Most of the endangerment is caused by habitat loss and degradation caused by dams, sedimentation, water pollution, dredging and other anthropogenic factors (Neves et al. 1997, Neves 1999). Without immediate efforts to recover the 70 federally listed and numerous other imperiled species in United States watersheds, the extinction of additional species is likely. With this goal in mind, a committee of experts prepared a National Strategy for the Conservation of Native Freshwater Mussels to coordinate a nationwide conservation program (National Native Mussel Conservation Committee, 1998). This document elaborates on the genetic concerns expressed in the national strategy.

Propagation and culture of endangered mussel species typically is recommended in recovery plans (e.g., US Fish and Wildlife Service (USFWS) 2004), to augment population sizes and to reintroduce species to sites within their historical ranges. A joint policy concerning controlled propagation was adopted by USFWS and the National Marine Fisheries Service (NMFS) to provide guidance and consistency for implementation of species recovery activities involving captive propagation (USFWS and NMFS, 2000). This policy recognizes controlled propagation as a useful tool for establishing new, self-sustaining populations; for supplementing or enhancing wild populations; and for holding offspring of listed species for part of their development if suitable natural conditions do not exist (USFWS and NMFS, 2000). Over the last 10 y, propagation technology has been developed at the Freshwater Mollusk Conservation Center at Virginia Polytechnic Institute and State University (Virginia Tech) and at other facilities in the United States to produce endangered juvenile mussels for this purpose (Neves 2004). Currently, 15 federal and state facilities propagate freshwater mussels in the Southeast and Midwest: Alabama Department of Conservation and Natural Resources, Kentucky Department of Fish and Wildlife Resources, Mammoth Cave National Park (Kentucky), University of Minnesota, North Carolina State University, Ohio State University, Southeast Aquarium Research Institute (Georgia), Southwest Missouri State University (SWMSU), Tennessee Tech University, USFWS Genoa National Fish Hatchery (Wisconsin), USFWS Mammoth Springs National Fish Hatchery (Arkansas), USFWS Warm Springs National Fish Hatchery (Georgia), USFWS White Sulphur Springs National Fish Hatchery (West Virginia), Virginia Department of Game and Inland Fisheries, and Virginia Tech University. These facilities have conducted critical life history studies on freshwater mussels (e.g., Jones & Neves 2002; Neves 2004) and, during the past several years, have released over 1 million juveniles of more than a dozen endangered species into rivers throughout the eastern United States. Survival of laboratory-reared juveniles 1-3 y of age after release already has been documented. For example, researchers at SWMSU produced thousands of juvenile Neosho mucker, Lampsilis rafinesqueana (Frierson, 1927), and reintroduced them in 2000 into historical habitat in the Fall and Verdigris rivers. Kansas. Biologists recovered 28 juveniles of this species at release sites in 2002 (C. Barnhart, SWMU, pers. comm. 2003). The endangered Higgin's-eye pearlymussel, Lampsilis higginsi (I. Lea 1857), and endangered oyster mussel, Epioblasma capsaeformis (I. Lea, 1834), have been propagated, outplanted, and recovered at release sites in the upper Mississippi River, Wisconsin, and Clinch River, Tennessee, respectively (R. Gordon, USFWS, Genoa National Fish Hatchery, pers. comm. 2002, Jones & Neves, unpubl, data, 2004). Therefore, propagation of mussels offers state and federal hatcheries an opportunity to expand their mission and assume an important role in conservation of biological diversity in the United States.