Vertical and horizontal distribution of juvenile Pacific whiting (Merluccius productus) in relation to hydrography off California

The vertical and horizontal distributional patterns of young-of-the-year juvenile Pacific whiting, Merluccius productus, collected during midwater trawl surveys off California from mid-May through mid-June 1986-95 were examined. Comparison of 1992 MOCNESS tows and depth-stratified midwater trawls indicated that although larvae were most abundant below the mixed layer, juveniles were most abundant in the upper mixed layer. Abundance estimates from the midwater trawl surveys varied from year to year. Large numbers were consistently observed in the Monterey Bay area. The least-squared mean catch per year from a sampling stratum offshore of Monterey Bay was significantly correlated with recruitment to the commercial fishery two years later, suggesting that midwater trawl surveys could provide useful fishery-independent forecasts of year-class strength. Information collected with CTD recorders in 1987-95 indicated that juveniles were significantly less abundant in upwelled water than in non-upwelled water. This could be attributed to advection away from upwelling fronts, a behavioral response to avoid upwelled water, or a general offshore distributional pattern, irrespective of upwelling events. Plots of juvenile abundances and density (sigma(t)) contours showed substantial catches nearshore during periods of upwelling relaxation, whereas nearshore abundances were greatly reduced during strong upwelling events.