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Project: Fish Community Responses to Climate Regime

Background and Objectives

During the past 35 years, the Southern California Bight (SCB) has experienced changing ocean conditions, due largely to the Pacific Decadal Oscillation (PDO) and two major El Niños. These climate cycles have variably affected the abundance of different fishes. Regional surveys of demersal fishes in the SCB during this period have provided data for assessing changes in fish abundance, bathymetric distribution, and the functional organization of communities. Most studies have focused on changes in the overall abundance of a species or its occurrence. Less well-known are bathymetric changes in species distribution and community organization occurring during these periods. This type of information provides a basis for distinguishing between natural and anthropogenic effects on fish communities.

The objective of the study was to determine bathymetric changes in functional organization of demersal fish communities on the southern California shelf during a PDO cycle and the 1997-1998 El Niño event. Specific objectives were to assess changes in bathymetric distribution of fish foraging guilds across the coastal shelf, and assess changes in the bathymetric distribution of expected dominant guilds.


This project was conducted in 2008.


The study utilized data from four large-scale surveys of demersal fish of the southern California coastal shelf from 10-200 m depth. The previous regional surveys were conducted in 1972-1973 (cold regime), 1994 (warm regime), 1998 (El Niño), and 2003 (cold regime). All fish were collected using semiballoon otter trawls, and then identified to species, measured, and weighed in bulk. For the purposes of this project, the latter three studies were compared to a baseline model of functional community organization developed with the 1972-1973 data. The functional structure model includes 18 foraging guilds (classified by habitat, feeding habits, and size) and describes their distribution at 20-m depth intervals.

Classification of foraging guilds of soft-bottom fishes on the southern California shelf (from Allen, 1982, 2006)


Examination of depth replacement patterns within foraging guilds provided a unique perspective for understanding disruptive effects and responses of demersal fish communities to changing ocean conditions. El Niño effects on bathymetric patterns included expansions or contractions of depth ranges of some guilds, retreats of some guilds or guild members to deeper water, and intrusions of new dominant guild members from the south. Changes between cold and warm regime periods were generally less pronounced but some gradual declines in the occurrence of deep-living guild members during the warm regime were apparent, suggesting decreased recruitment from the north. Patterns of several guilds were identical or nearly so during the two cold regimes, suggesting a resilient return to baseline cold regime patterns.


M.J. Allen. 2009. Influence of Climate Patterns on Southern California Fish Communities. Presented at 2nd Annual SCCWRP Symposium.

For more information on Fish Community Responses to Climate Regime, contact Ken Schiff at (714) 755-3202.
This page was last updated on: 7/1/2014