Loss of Top Predators and Diversity from 2003 to 2009 Indicates Rapid and Important Changes the Community Structure of Groundfishes in the California Current Ecosystem

Groundfishes are an important component of the California Current ecosystem because of their ecological importance and their high value as recreational and commercial fisheries. Here I examine how the west coast groundfish community changed from 2003 to 2009 using data from the West Coast Groundfish Survey.  Data were binned into three trophic levels (<3.5, 3.5-3.99, 4.0+), three depth strata (shelf, upper slope, lower slope) and four latitude zones (south of Pt Conception, to Cape Mendocino, to Cape Blanco, to Cape Flattery) to examine changes in biomass, Shannon diversity, species richness and Pielou’s evenness through time.

Biomass (CPUE) for all three trophic levels declined on the shelf north of Pt Conception, while biomass for low trophic level fishes (<3.5) increased in northerly slope regions.  Declines of top predators (TL 4.0+) in the northern most shelf bin were stronger than declines for other groups, and these fishes made up proportionally less of the total biomass in 2009 than in 2003.  Top predators did not show a decline in Shannon diversity, but in the more northern areas richness declined as evenness increased. Shannon diversity for mid-trophic level fishes (3.5-3.99) declined on the shelf across all latitudes with this decline being due to both lower richness and lower evenness.  Taken together, these results indicate important structural changes in the groundfish community, especially in more northerly areas on the continental shelf.