FISH ASSEMBLAGES AS INDICATORS OF ENVIRONMENTAL DEGRADATION IN MARYLAND COASTAL-PLAIN STREAMS

Effects of anthropogenic stream degradation on fish assemblages in coa stal plain streams of Maryland were investigated by using data from 19 89-1993. Fish assemblages, stream physical habitat, and water quality were assessed concurrently at 69 sites. Through the use of habitat and water quality information, two groups were selected from the data set to represent least-impacted streams (N = 16) and most-impacted stream s (N = 22). Impacts ranged from agricultural activities involving chan nelization and riparian destruction to altered hydrologic regime and c hannel modification related to urban development. Differences in fish assemblages between the two groups indicated that the degraded streams were less diverse and were dominated by a few tolerant taxa, whereas higher-quality sites were characterized by a more balanced assemblage structure and trophic composition, as well as by higher indigenous cyp rinid richness and abundance. Various metrics, based on assemblage str ucture and function under a guild approach, were tested for difference s between the high- and low-quality stream groups. The metrics that ex hibited the greatest discrimination between groups reflected greater d iversity and abundance, a balanced trophic structure, and lower abunda nce of species considered tolerant to environmental degradation. The m ost effective metrics included the number of intolerant species presen t, the number of shiner species, the proportion of silt-intolerant spa wners in the assemblage, the proportion of tolerant fishes, and the pr oportion of insectivorous cyprinids. The metrics that demonstrated abi lity to discriminate high- and low-quality streams are proposed for de velopment into biological indicators for this region.