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-ye ar juvenile Pacific whiting, Merluccius productus, collected during mi dwater trawl surveys off California from mid-May through mid-June 1986 -95 were examined. Comparison of 1992 MOCNESS tows and depth-stratifie d midwater trawls indicated that although larvae were most abundant be low the mixed layer, juveniles were most abundant in the upper mixed l ayer. 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 strat um offshore of Monterey Bay was significantly correlated with recruitm ent to the commercial fishery two years later, suggesting that midwate r 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 upwell ed water than in non-upwelled water. This could be attributed to advec tion away from upwelling fronts, a behavioral response to avoid upwell ed water, or a general offshore distributional pattern, irrespective o f upwelling events. Plots of juvenile abundances and density (sigma(t) ) contours showed substantial catches nearshore during periods of upwe lling relaxation, whereas nearshore abundances were greatly reduced du ring strong upwelling events.