Assessing the relationship between urban land use on fish assemblages of San Francisco Bay streams

There are approximately 70 small streams that flow directly into the San Francisco Bay (Bay), many of which are surrounded by highly urbanized landscapes. Urban development often leads to altered hydrographs and stream channel morphology, and high concentrations of contaminants. These physical changes can have ecological consequences. Broad scale spatial analyses utilizing GIS tools can be useful in elucidating correlations between land use and fish communities. Using a dataset of stream fishes collected at 275 sites throughout the Bay region from 1993-1999, we characterized fish assemblage data into multiple metrics and used GIS tools to characterize the composition and configuration of land cover for individual sub-watershed basins at multiple scales. Finally, we used a multivariate approach to analyze the relationships between land use and fish assemblage metrics. Preliminary results in the largest watershed draining to the Bay (Alameda Creek) reveal that the number and percentage of nonnative individuals are positively associated with sub-watersheds characterized by high percentages of developed land. In larger sub-watersheds, there were stronger associations between land use composition and fish metrics when we limited our analysis to local land use. Multivariate analyses also indicated that the addition of local stream habitat variables to the land use model better predicted the presence of nonnative fishes. Ongoing work is focused on understanding whether these same patterns emerge when considering the entire Bay region. We suggest that managers consider both the composition of altered landscapes and their configuration within the landscape to better conserve native fish communities in urbanized regions.