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Abstract
North Americas rich freshwater fish fauna continues to decline, in part due to excessive sedimentation in streams and rivers. The objective of this dissertation was to investigate the effects of elevated suspended sediment concentration (SSC) on the spotfin chub (Erimonax monachus), an imperiled southern Appalachian minnow, and on a surrogate species, the whitetail shiner (Cyprinella galactura). Using a multi-tank sediment-suspension apparatus, a whole-body cortisol assay and spectral confocal microscopy, I investigated the effects of SSC (0, 25, 50, 100, and 500 mg/L) on the stress response (cortisol concentration), specific growth rate (percent change in mass per day), and gill condition (i.e., lamellar thickness and interlamellar area) of young-of-year (YOY) spotfin chubs and whitetail shiners. I also examined the effects of SSC on the spawning success of whitetail shiners. In the upper Little Tennessee River (LTR), I determined spotfin chub spawning habitat character and extent and tested the feasibility of supplementing spawning through the creation of artificial spawning sites. In the laboratory the sediment-suspension apparatus maintained SSCs within 95% of target values, thus providing controlled conditions for these studies, while not producing excessive turbulence. Exposure of YOY to elevated SSC caused a significant increase in cortisol levels, in both species and a significant decrease in growth rate at three life stages (2, 4, and 8 months of age). Increased SSC elicited a stress response in spotfin chubs 3-fold higher than controls; this response was similar to previous accounts of rainbow trout exposed to acute handling stress. For spotfin chubs, a 15-fold decrease in specific growth rate occurred at the highest SSC (500 mg/L). Gill damage observed by quantitative confocal microscopy was minimal at 0, 25, and 50 mg/L, moderate at 100 mg/L, and severe at 500 mg/L. Specific growth rate was significantly and inversely related to increasing gill lamellar thickness. Whitetail shiner spawning effort decreased from 88% in control tanks to 50% in 500 mg/L tanks. Total spawning output at 500 mg/L SSC was only 10% of that in controls, and fish delayed reproduction until SSCs were lower. The number of propagules spawned decreased significantly with increasing mean SSC above 25 mg/L. In the upper LTR, discharge is sufficient to increase SSCs above 100 mg/L > 50% of the year, and above 500 mg/L > 10% of the year. Therefore, SSC treatments that elicited negative effects on stress, growth, and spawning success are likely to be experienced by spotfin chub populations in the field. In the upper LTR, most spotfin chub spawning was located in swift, moderately deep bedrock riffles that were devoid of fine sediment. However, spotfin chub nests were also located in slow, shallow habitats with 25-50% fine sediment (< 2mm). Spotfin chub spawning was limited to ~ 4.4% of the riverbed; this is twice previous estimates. The distance between spawning habitat patches was ~ 10 100 m. The distance between localized groups of habitat patches ranged from 194 1840 m. Of 50 supplemented spawning rocks, one was used for a nest and two more were guarded by nuptial males. Spawning habitat enhancement may be an inexpensive means of increasing reproductive success among imperiled native fishes. Increased SSC was shown to negatively affect the stress response, growth rate, gill condition and spawning