Effects of ephemeral circulation on recruitment and connectivity of nearshore fish populations spanning Southern and Baja California

Abstract

The California sheephead Semicossyphus pulcher and the kelp bass Paralabrax clathratus are members of a suite of nearshore reef species that have subtropical taxonomic affiliations and important fisheries in the Southern California Bight (SCB). This suite shows high interannual fluctuation in recruitment success in the SCB, with no known cause. One hypothesis gaining mention in management literature is the idea that recruitment booms in the SCB originate from larvae swept poleward from Mexico during El Nio flow-reversal events. If true, SCB stocks may be reliant on Mexican sources. We used 3 diverse sources of data to investigate the likelihood of El Nio-driven recruitment success and connectivity for S. pulcher and P. clathratus. Time series of larval abundance revealed that neither species shows synchrony with El Nio Southern Oscillation (ENSO) cycles that would suggest influx of Mexican larvae during El Nio flow reversals. P. clathratus age structure data show that recruitment strength is unrelated to ENSO cycles but correlates to spring sea surface temperature in the SCB, indicating that local environmental factors drive interannual variation in local production. Genetic analyses of 14 populations of P. clathratus with 7 microsatellite loci revealed distinct patterns of genetic structure in the SCB and Baja California that reflect localized connectivity patterns and contradict patterns that would be expected if dispersal primarily occurred during El Nio flow reversals. While these results support the importance of protecting local sources in the SCB, continued study of dispersal and recruitment at large scales will help characterize the causes of interannual variation and the exact scale of cross-border connectivity.