7405 - Laserfiche WebLink

Home Browse Search

38 BIOLOGICAL REPORT 90(5) Discharge versus Habitat in Steep-gradient Piedmont Streams by Jeffrey W. Foltz Department of Aquaculture, Fisheries, and Wildlife Clemson University Clemson, South Carolina 29634 The focus of previous, ongoing, and future stream fish habitat research is the relation of the fish com- munity to substrate composition, water depth, and water velocity. My basic premise has been that a diverse habitat will support a diverse fish community if water quality is suitable. Mter many years we have come to expect reductions in fish species diver- sity following catastrophic changes to a stream's habitat, such as channelization. Fishes of the Pied- mont in the southeastern United States may be divided into three broad categories of habitat users: sculpins (Cottus spp.) and darters (Etheostoma spp. and Percina spp.), which prefer swift waters of rif- fles; minnows and suckers, which use open runs and midstream pools; and sunfishes (Lepomis spp.) and basses (Micropterus spp.), which seek cover near undercut banks and jams. These three broad categories of habitat are defined largely in terms of water velocity and depth. Substrate diversity is also important, not only because it provides a variety of spawning habitat for fishes, but also because it is the primary site of aquatic insect productivity. The ratio of riffles to pools is thought to represent a fundamental characteristic of a stream ecosystem. A cross section or transect across a Piedmont stream or river frequently produces a series or mix- ture of small pools and riffles. Whereas a pool by itself might serve as a feeding station for a predatory fish, suitability of the pool depends on its proximity to a riffle in order to provide drifting in- sects. The original riffle-pool concept was theorized as a longitudinal phenomenon; however, a balance of riffles and pools at an acceptable level (e.g., at a ratio equal to that at median flow) might very well be necessary for maintenance of a diverse fish community. Longitudinal increases in fish species diversity are well known. In my research, fish species diversity was predictable from substrate diversity, and sub- strate diversity increased downstream. Fish abun- dance (Le., catch per unit effort) was positively related to width, depth, and percent cobble (Le., rubble) and negatively related to percent bedrock and percent silt and sand in the substrate. Currently, I am researching (1) the relation between discharge and diversity of velocity-depth combinations, (2) the relation between discharge and the riffle-pool ratio, (3) how relations 1 and 2 are related to conventional wetted perimeter-discharge curves, and (4) fish community diversity in relation to velocity-depth diversity and the riffle-pool ratio. Field methods involve placing numerous transects in a study section and measuring velocity, depth, and sub- strate at 1-m intervals along each transect. Subse- quently, each interval is categorized into 1 of 13 categories, which include dry, 3 riffle categories, 5 pool categories, and 4 categories of runs. Velocity-depth diversity seems to gradually decline with reductions in discharge, and it collapses near the inflection point on wetted perimeter-discharge curves. This reduction is primarily due to reduction in the 4 categories of runs. The riffle-pool ratio remains generally flat with reductions in discharge, but collapses near the wetted perimeter-discharge inflection point. Information Sources Deacon, J. E., and W. G. Bradley. 1972. Ecological distribution of fishes of the Moapa River in Clark Co., Nevada. Trans. Am. Fish. Soc. 101:408-419. Fausch, K. D., C. L. Hawkes, and M. G. Parsons. 1988. Models that predict standing crop of stream fish from habitat variables: 1950-1985. U.S. For. Serv., Pac. Northwest Res. Stn. Gen. Tech. Rep. PNW-GTR-213. 52pp. Foltz, J. W. 1982. Fish species diversity and abundance in relation to stream habitat characteristics. Proc. Annu. Conf. Southeast. Assoc. Fish Wildl. Agencies 36:305-311. Fraser, J. C. 1972. Regulated stream discharge for fish and other aquatic resources-an annotated bibliography. F AO Fish. Tech. Pap. 112. 103 pp.