Climate Change Vulnerability of Freshwater Fishes in the San Francisco Bay Area

Abstract

Climate change is expected to progressively shift the freshwater environments of the San Francisco Bay Area (SFBA) to states that favor alien fishes over native species. Native species likely will have more limited distributions and some may be extirpated. Stream-dependent species may decline as portions of streams dry or become warmer due to lower flows and increased air temperatures. However, factors other than climate change may pose a more immediate threat to native fishes. Comparison of regional vs. statewide vulnerability (baseline and climate change) scores suggests that a higher proportion (56% vs. 50%) of SFBA native species, as compared to the state's entire fish fauna, are vulnerable to existing anthropogenic threats that result in habitat degradation. In comparison, a smaller proportion of SFBA native species are vulnerable to predicted climate change effects (67% vs. 82%). In the SFBA, adverse effects from climate change likely come second to estuarine alteration, agriculture, and dams. However, the relative effect of climate change on species likely will grow in an increasingly warmer and drier California. Maintaining representative assemblages of native fishes may require providing flow regimes downstream from dams that reflect more natural hydrographs, extensive riparian, stream, and estuarine habitat restoration, and other management actions, such as modification of hatchery operations. KEY WORDSvulnerability assessment, native fishes, alien species INTRODUCTIONIn a recent paper, we suggested that a majority of California's native inland (largely freshwater) fishes will be hastened to extinction by climate change effects on already deteriorating populations (Moyle et al. 2013). We also presented a methodology to systematically evaluate vulnerability to extinction or extirpation as a result of baseline conditions (i.e., existing anthropogenic threats) and to new conditions created by climate change (e.g., warmer temperatures, altered stream flows). But climate change is not affecting California uniformly. Regions within the state will experience alterations to temperature and hydrologic patterns in different ways (e.g., Cayan et al. 2008), depending, for example, on their proximity to the ocean or median elevation. Existing threats to freshwater fishes (as defined in Moyle 2002) also differ among regions of the state. Consequently, vulnerability of species to extinction or extirpation must be assessed at regional scales in order to increase the efficacy of conservation actions. Here, we rate baseline, climate change, and overall vulnerabilities (as in Moyle et al. 2013) Freshwater fishes in SFBA represent a regional fish fauna that has been well-studied (Moyle 2002;Leidy 2007;Cloern and Jassby 2012). The extant SFBA inland fish fauna is comprised of about equal parts native (25) and alien (23) species (Tables 1 and 2). The status of pink (Oncorhynchus gorbuscha) and chum (O. keta) salmon in the area is uncertain and so they were not included in our analysis. The aquatic ecosystems of wh...

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Sensitivities of an endemic, endangered California smelt and two non-native fishes to serial increases in temperature and salinity: implications for shifting community structure with climate change

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