Influence of instream physical habitat and water quality on the survival and occurrence of the endangered Cape Fear shiner.
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Date
2003-07-16
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Abstract
The Cape Fear shiner Notropis mekistocholas is a recently described cyprinid fish endemic to the Cape Fear River Basin of North Carolina. Only five declining populations of the fish remain, and therefore, it has been listed as endangered by the U.S. Government. Determining habitat requirements of the Cape Fear shiner, including physical habitat and water quality, is critical to the species' survival and future restoration. This study integrated the sciences of toxicology and conservation biology, and simultaneously assessed ecosystem level influences of habitat (water and physical environments) on survival, growth, occurrence, and distribution of the Cape Fear shiner. I conducted an instream microhabitat suitability analysis among five sites on the Rocky and Deep rivers to (1) quantify Cape Fear shiner microhabitat use, availability, and suitability in extant habitats, (2) determine if physical habitat alterations are a likely cause of extirpation of the Cape Fear shiner at historical locations and if instream habitat is a limiting factor to occurrence and survival of the species in extant habitats and at potential reintroduction sites, and (3) estimate population density at selected extant sites. I used an in situ 28-day bioassay with captively propagated Cape Fear shiners to (1) determine if water quality is a limiting factor to the occurrence, growth, and survival of the Cape Fear shiner, (2) document habitat suitability by assessing inorganic and organic contaminants through chemical analyses and review of existing data, and (3) assess the protectiveness of water quality standards for primary pollutants based on comparisons of laboratory, field toxicity, and water chemistry data.
Cape Fear shiners most frequently occupied riffles and velocity breaks (i.e., areas of swift water adjacent to slow water), moderate depths, and gravel substrates. They used habitat non-randomly with respect to available habitat, and habitat use was similar between post-spawning and spawning seasons. However, Cape Fear shiners shifted to shallower depths during the spawning season, suggesting that adequate depth distribution may be an important element of Cape Fear shiner habitat. Comparisons of suitable microhabitat among river reaches where the Cape Fear shiner is extant, rare, or extirpated suggest that suitable substrate (gravel) may be lacking where the fish is rare, and that suitable microhabitat combinations, especially for water velocity, are rare at all sites. Cape Fear shiner density was too low to be estimated in upstream reaches of the Deep River where gravel substrate is limited. Population density ranged from 795 fish/ha to 1,393 fish/ha at three sites surveyed.
Potential reintroduction sites had shallower mean depths than those at extant sites, and the extirpated site on the Rocky River contained the most suitable physical habitat, but lacked adequate water quality. A site on the Deep River where the species persists, but is rare, is a candidate reach for habitat restoration, but would require substrate alteration to improve conditions for the Cape Fear shiner.
After conclusion of the 28-day in situ test, I measured fish survival, growth (an increase in total length), and contaminant accumulation. Survival of caged fish averaged 76% and ranged from 53% to 100%. Sites with the greatest mean survival were on the Deep River (87%), followed by those on the Rocky River (74%), and were lowest on the Haw River (66%). Fish survival was significantly lower at five sites, two in the Haw River, two in the Rocky River, and one in the Deep River. Caged fish grew significantly at four of the 10 sites, and all fish accumulated quantities of Cd, Hg, PCBs, DDTs, and other contaminants over the test duration. Results from the in situ exposures indicate that a reintroduction site on the Rocky River does not have adequate water quality to support reintroduction, yet results from the instream habitat assessment indicate that physical habitat is similar to extant Cape Fear shiner locations.
Finally, the survival and recovery of the Cape Fear shiner is dependent upon the successful protection of remaining suitable physical habitat and water quality that will require broad-scale examination and approaches considering physical instream habitat, water quality and contaminants, biotic interactions with other organisms, as well as human uses and alterations of the river, riparian zone, and watershed.
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Keywords
endangered species, Cape Fear shiner, in situ, toxicology, habitat suitability, conservation, population density
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Degree
MS
Discipline
Zoology
