Development and Assessment of a Sampling Design for Mussel Assemblages in Large Streams
Christian, Alan D., Harris, John L., The American Midland Naturalist
Freshwater mussel beds of the lower 68 km of the Cache River, Arkansas, were delineated, sampled using dive techniques and a stratified random sampling methodology and analyzed for density and species richness. A total of 38 mussel beds were delineated, 14 major beds (Mbeds) and 24 minor beds (mbeds), and defined by areal extent and mussel density. Analysis of our sampling precision indicated 80% or better confidence levels for a majority of our sites and suggested that a sample size of 15 1-m^sup 2^ quadrats is sufficient to obtain 80% or better confidence. Our large river diver-assisted sampling methodology has been shown to be a useful and appropriate methodology for obtaining large geographic scale baseline distribution (bed and species), species richness, density and population and community numerical standing crop estimates information where tradeoffs are required in order to complete a project within time and budget constraints.
Over 300 species of freshwater pearly mussels reside in the continental United States (Turgeon et al., 1998). However, within the last 50 y, this rich fauna has been decimated by impoundments, sedimentation, channelization, dredging, water pollution and invasive species (National Native Mussel Conservation Committee, 1998). Approximately 67% of the freshwater mussel species in the United States are vulnerable to extinction or are already extinct, and more than 1 in 10 species may have become extinct in this century (Williams et al., 1993; Bogan, 1997; Master et al., 1998).
Freshwater mussels are renewable resources that provide both ecological and economic benefits. They are ecologically important as a food source for aquatic and terrestrial animals, improve water quality by filtering contaminants, sediments and nutrients from aquatic systems and serve as an early warning system for water quality problems (National Native Mussel Conservation Committee, 1998; Vaughn and Hakenkamp, 2001). Currently, endangered species are regarded as indicator organisms in an ecosystem and efforts are being made to preserve not only the species and its habitat, but as much of the entire ecosystem as possible in order to prevent further degradation (Walters, 1992, 1993; Anderson, 1993; Doppelt, 1993; Rich ter, 1993). Economic benefits have been derived historically from the harvest of pearls and the production of buttons from shells. Recent economic benefits are found in the sale of mussels to the Far East where they are formed into beads for the thriving cultured pearl industry. However, the demand for beads has declined since 1995 due to the loss of the Akoya pearl oysters in Japan and new techniques for cultured pearl production in China, reducing the $50 million dollar industry of the mid 1990s to a much lesser valued industry (Neves, 1999).
In order to conserve native freshwater mussels in the U.S., the National Native Mussel Conservation Committee (1998) identified 10 specific problems. Among these problems was the lack of knowledge regarding current distribution and health of mussel populations (Problem 4). Strategies 4.1-4.3 regarding alleviation of this problem are germane to this study. These strategies include: (4.1) determining location, density, species composition and status of existing mussel communities, (4.2) gathering historic mussel distribution data and making it readily available and (4.3) gathering information on the occurrence and abundance of mussel stocks that have value for the commercial mussel industry. Surveys that address this problem have proliferated in recent years (Williams and Schuster, 1989; Ahlstedt and McDonough, 1993; Miller et al., 1993; Siemsen, 1993; Ahlstedt and Tuberville, 1997).
Historically, status surveys for freshwater mussels usually consisted of wading in a stream or walking along the stream bank picking up live mussels or relic shells (e.g., Gordon, 1982; Hoggarth, 1992; Walters, 1994), which would hamper collecting from deeper and/or more turbid waters. …