Faunal shift in southern Californiaʹs coastal fishes: A new assemblage and trophic structure takes hold

Trends in coastal fish abundance indices were examined using a novel 39-year (1972–2010) time series recorded at southern California coastal power plants. Since 1972, the annual mean abundance index significantly declined (r2 = 0.45, p < 0.001). The mean annual biomass index likewise declined but with a large interruption in 2005–2006 when an influx of large bodied, southern species increased the annual means. Ensemble mean abundance indices for fished and unfished species declined at similar rates. Two faunal shifts were identified, 1983–1984 and 1989–1990. The ensemble mean, annual entrapment rate abundance index during the current period (1990–2010) represents only 22% of that recorded during the first and most abundant period, 1972–1983. The mean biogeographic distribution of the assemblage was non-linear over time including a shift south during the 1980s through the 1990s before shifting north in recent years. The northern shift in recent years accompanied higher variability than previously recorded and was likely related to the overall low abundance. Since the early 1980s, the mean trophic level derived from abundance declined. The observed patterns were not correlated with commonly employed composite indices such as the Pacific Decadal Oscillation, but did show some sensitivity to changes in coastal seawater temperature and density over time. Timing of the observed faunal shifts in the fish assemblage was consistent with reported oceanographic shifts. These data suggested factors beyond fishing, such as oceanographic change, have substantially impacted the coastal fishes of southern California.