Population Density and Instream Habitat Suitability of the Endangered Cape Fear Shiner

—The Cape Fear shiner Notropis mekistocholas is an endangered minnow endemic to the Cape Fear River basin of North Carolina; only five populations remain, all of which are declining. Determining the population densities and habitat requirements of the species is critical to its survival and restoration planning. We conducted population surveys (four sites) and instream microhabitat suitability analyses (six sites) on the Rocky and Deep rivers to (1) estimate the population density of Cape Fear shiners, (2) quantify the use, availability, and suitability of microhabitats, and (3) determine whether physical habitat alterations were a likely cause of local extirpations and whether instream habitat limits the occurrence and density of this species. Density ranged from 795 fish/ha to 1,393 fish/ha (4,768–7,392 fish/km) at three of the sites surveyed and was too low to be estimated at the fourth site. The fish most frequently occupied riffles and velocity breaks at moderate depths over gravel substrates. It occupied microhabitats nonrandomly with respect to availability; the microhabitats occupied were similar between spawning and postspawning seasons but shallower during spawning. Comparisons of suitable habitat among sites where the fish is extant, rare, or extirpated suggest that suitable substrate (gravel) is lacking where the fish is rare and that suitable microhabitat combinations, especially with respect to water velocity, are rare at all sites. Potential reintroduction sites where the species is rare or extirpated were shallower than extant sites, and one site where the fish is extirpated contained suitable physical habitat but lacked adequate water quality. Another site where the species is rare would require substrate alteration to improve conditions. The survival and recovery of the Cape Fear shiner is dependent on the protection of remaining suitable physical habitat with approaches that consider instream habitat, water quality, and biotic interactions as well as human uses and alterations of the river, riparian zone, and watershed. Freshwater fishes are among the most diverse of vertebrate groups, but they are also one of the most vulnerable due to widespread degradation of aquatic ecosystems (Angermeier 1995; Warren et al. 2000; Duncan and Lockwood 2001). The drainage basins of the southern United States contain the greatest diversity and number of endemic freshwater fishes in North America north of Mexico, and many populations are declining; 28% (187 taxa) are recognized as extinct, endangered, threatened, or vulnerable to extinction (Burr and Mayden 1992; Warren et al. 1997, 2000). The growing imperilment of fishes and other aquatic fauna is predominantly due to human-mediated changes within watersheds including construction of impoundments, water withdrawals, urbanization, land use alterations, and environmental pollution (Moyle and Leidy 1992; Burkhead et al. 1997; Burkhead and Jelks