Climate-Driven Changes in Southern California Coastal Fishes, 1972-2009

Global, oceanic, capture fisheries are declining, but little information is available on the status of coastal, minimally-harvested species. We used a novel, 38 year (1972-2009) time-series of coastal fish abundance estimates recorded during entrapment monitoring at five coastal power plants that utilize once-through-cooling to study variations in species-specific trends. This time series encompassed ~170 km of the Southern California coastline and large-scale, low-frequency oceanographic variations including a long-term warming trend. Twenty-one species make up 98% of the 13 million fish recorded. The ensemble mean, annual entrapment rate declined 95% from 1972 (693/10⁶ m³ ± 327, SE) to 2009 (34/10⁶ m³ ± 10). These data document a marked decline in abundances and a faunal shift, in close association with ocean warming. The first principal component (PC1) accounted for 29% of the variation and was significantly correlated with SST (R² = 0.51). Annual PC1 scores further indicate a transition from a cold regime to a warm regime separated by a ~decade-long transitional period from 1976-1986. The regime designations were made based on the community composition and their species-specific relationships with each other and SST. Percent similarity index (PSI) analysis revealed a shift from a relatively stable PSI to a highly variable PSI in the late-1990s. PSI by years separating the survey indicated a rapid decay in similarity between years ultimately reaching an asymptote at circa 10 years separation. The limited capture fishery importance suggests these patterns of change are due to effects of environmental dynamics rather than harvesting.