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Aquatic Species

Several agencies and conservation organizations track the distribution and conservation status of species in the United States. The U.S. Fish and Wildlife Service (USFWS) maintains a list of species that have officially been proposed or listed threatened or endangered under the Endangered Species Act of 1976, as amended. They also track species, called candidates, for which insufficient information exists to warrant formal listing. Before species are added to the list, their present and historic status must be thoroughly evaluated, and the public must be given the opportunity to provide input about proposed listings. For this reason, years often go by from the time the species is petitioned or proposed for listing until it is officially listed in the Federal Register as threatened or endangered. These procedural requirements may delay or even prevent some species from being listed.

Another ranking is managed by the Association for Biodiversity Information (ABI). The ABI is a nonprofit organization founded by The Nature Conservancy and the Natural Heritage Network (NatureServe 2000, Stein and others 2000). The list managed by ABI is more inclusive, and uses standardized criteria in an attempt to objectively rank individual species across their native ranges. This global ranking, or G rank, ascribes a degree of vulnerability to extinction throughout the entire range of the species. Table 23.1 gives the definitions used by ABI for the G ranks. Because this Assessment is concerned with rangewide sustainability, only species with ranks of G3 and lower (including GX and GH) were included (table 23.2) (fig. 23.1). Species ranked G4 or higher are apparently secure throughout their native ranges at present. ABI updates its list three times a year, and experts review the status of all listed species and potential new entries. The USFWS draws upon ABI information and on many of the same experts for updates to its list. The ABI source was used for this Assessment to produce the list of potentially imperiled aquatic species because it is generally more current and comprehensive than the USFWS list. This list was supplemented by six fish and three crayfish from American Fisheries Society (AFS) expert committees on the status of crayfish, mussels, and fish (Taylor and others 1996; Williams and others 1989, 1993).

Additionally, only species that spend a portion of their life cycle in a freshwater environment, including crustaceans, insects, snails, mussels, fish amphibians, and reptiles were included in this chapter. Finally, we needed adequate information to evaluate species distributions and life histories. Species with a “?” or “Q” following their G rank were not included in the lists produced for this Assessment. Table 23.2 displays the percentage of each taxonomic group that had inadequate information. While these latter species were omitted from this Assessment, their importance should not be overlooked. Many of these animals, in fact, may be extremely imperiled. The lack of distributional, taxonomic, and ecological information on these species represents a major data gap for aquatic species in the South.

The ABI database was searched for seven groups of aquatic animals: crustaceans, insects, snails, mussels, fish, amphibians, and reptiles. Search dates were May 15, 16, and 17, 2000 for all seven groups. A major update to the database was incorporated by ABI several months later. Second searches were conducted on July 15, 2001, for mussels and August 17, 2001, for insects. The results of these searches were used in this Assessment. Table 23.2 lists the taxonomic groupings, and figure 23.1 displays relative proportion of the 864 rare aquatic species selected by the criteria listed above. The lists of crayfish, mussels, and fish were compared to lists of vulnerable species published by the AFS (Taylor and others 1996, Warren and others 2000, Williams and others 1993). The AFS lists excluded the Rio Grande watershed. The only other differences between the AFS and ABI lists were six fish and three crayfish, which were added to the ABI list and considered in this Assessment. The mussel lists were in complete agreement.

With the exception of insects, the number of species ranked G1 to G5 displayed in table 23.2 represents a close approximation of the number of described species in each of the taxonomic groups in the South.