Relations between Fish Assemblages and Urbanization in Southern California Coastal Streams
Cindy J. Lin and Richard F. Ambrose
Abstract.—Data collected as part of two studies to examine the influences of landscape modification on the ecology of three coastal Southern California river systems—the Calleguas Creek, Malibu Creek, and Santa Clara River watersheds—provided the opportunity to examine relations between urbanization and fish assemblages in Southern California coastal streams. Fish were collected at 63 sites from 1999 to 2001. Watershed land use was determined and classified into three land use types: agriculture, developed, and open space. Seven fish assemblage metrics were examined, including species richness, number of native and alien species, total fish abundance, percent abundance of native and alien species, and percent abundance of arroyo chub Gila orcuttii. Ten fish species were collected, and arroyo chub was the only species collected in all three watersheds. Native species included arroyo chub, threespine stickleback Gasterosteus aculeatus, steelhead Oncorhynchus mykiss, and Pacific staghorn sculpin Leptocottus armatus. There were no significant differences in fish assemblage metrics among the three land-use types. Both wetted stream width and depth were significantly related to native fish abundance. Results from this study suggest that the relatively species poor fish assemblages of Southern California may not be sensitive to watershed land use disturbance, but may be sensitive to local hydrologic conditions.