Declines in regional fish populations: have species responded similarly to environmental change?

Andrew J. Brooks, Russell J. Schmitt and Sally J. Holbrook

Abstract

Abundances of many coastal species off southern California have undergone dramatic declines over the past two decades concurrent with a regional climate shift. This shift in climatic conditions represents a natural, large-scale perturbation and provides an opportunity to understand whether and how various components of coastal ecosystems respond. We conducted time-series analyses on long-term data sets of non-exploited fish populations from the Southern California Bight to describe their temporal trends and explore the timing and magnitude of change. The species examined were classified as to trophic level, mode of reproduction, extent of geographic range, association with benthic or pelagic food webs, and habitat. In general, the magnitude of decline was similar for all species, regardless of classification. Trends were similar at all locations examined within the Bight, suggesting regional declines in abundances rather than redistribution of individuals. These patterns are consistent with the explanation that a regional decline in productivity associated with the shift to an alternate climatic regime is responsible for regional decline in fish stocks.

Keywords: Southern California Bight, regime shift, productivity, community organization, impingement

Marine and Freshwater Research 53(2) 189 - 198 (2002) doi:10.1071/MF01153