Patterns of coastal eddy circulation and abundance of pelagic juvenile fish in the Santa Barbara Channel, California, USA

Annual midwater trawling surveys (sampling at depths of 20 to 40 m) in early summer 1998 and 1999 revealed strong interannual variability in the patterns of abundance of late-stage larval and juvenile fishes in the Santa Barbara Channel. In June 1998, sampling revealed high concentrations of fishes in the center of a cyclonic eddy in the western Channel corresponding to the lowest dynamic height in the study area. In contrast, eddy circulation was not consistent during the second survey in June 1999, and high concentrations of fishes were not observed. Patterns of evolving surface currents, observed by high frequency radar and concurrent CTD sampling during the trawling surveys, suggest that interannual variability in fish abundance within the Santa Barbara Channel resulted from local retention in 1998, but not in 1999. Time series of relative vorticity (a measure of eddy rotation) computed from surface current fields indicates that the cyclonic eddy observed during the 1998 survey was a stable, persistent feature developing about 6 wk before the trawling surveys. We speculate that the closed circulation of the eddy in 1998 retained larval and juvenile fishes from about late April until late June. In 1999, trains of smaller eddies propagated across the region beginning in mid-May, lasting through the survey period. Given their size and circulation strength, the propagating eddies probably disrupted the closed circulation in the western Channel. These observations indicate a strong link between coastal mesoscale flows and spatial abundance patterns of juvenile and late-stage larval fishes.