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

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.