Persistence of native fishes in small streams of the urbanized San Francisco Estuary, California: acknowledging the role of urban streams in native fish conservation

Abstract

ABSTRACT Urbanization is known to have pernicious consequences for native stream fishes globally. The San Francisco Estuary (SFE), California, is one of the largest, most urbanized estuaries in North America and non‐native freshwater fishes are widespread in many of its catchments. Nevertheless, a diverse native and endemic freshwater fish species assemblage remains in this region. Historical records (1854–2007) were reviewed and sampling conducted throughout SFE catchments to determine the distribution of stream fishes. Native stream fishes were classified by zoogeographic type, habitat preferences, physiological tolerances, and whether native fishes utilized reservoirs during their life cycle. From 1993–1999, stream fishes were sampled at 270 sites distributed in 23 SFE catchments to assess the overall status and distribution of native stream fishes, and illuminate drivers of persistence. In 2009, stream fishes were sampled at 65 sites within the largest estuary catchment, Alameda Creek, to further explore distributional patterns and drivers of native fish persistence. Native stream fishes persist in the urbanized SFE because of several interacting factors, including the existence of extensive undeveloped landscapes in the headwaters of many catchments, the prevalence of saltwater dispersant native stream fishes, the wide physiological tolerances of native species, the presence of saltwater barriers between catchments that presumably reduces the spread of non‐native fishes, and the existence of reservoirs that function as habitat for several native species. These results emerged from both the SFE‐wide and the Alameda Creek analyses, suggesting they are somewhat general for this region. Study results show that streams in spatially complex urban settings retain important conservation benefits to native stream fishes, despite significant perturbations and the establishment of non‐native fishes.Copyright © 2011 John Wiley & Sons, Ltd.