The distribution of pelagic juvenile rockfish of the genus Sebastes in the upwelling region off Central California

Abstract

Many species of central California rockfishes conclude their pelagic stage during the spring-summer upwelling period, when advection of surface waters could carry them away from nearshore postpelagic habitats. We examined the distributions of late-stage pelagic juvenile rockfish in April and May/June of 1987 and 1988, based on midwater-trawl surveys between Point Reyes and Monterey Bay, California. Distributional patterns were complex, and changed rapidly with changing oceanographic conditions and with changes in species and size composition. The smallest pelagic juveniles often appeared offshore, in the region of the upwelling front, which suggested that they had been advected offshore at some time during upwelling. However, few pelagic juveniles were found offshore of the upwelling front. Larger pelagic juveniles were often found close to shore, even when upwelling was active. This suggests that later-stage pelagic juveniles undergo behavioral changes that enable them to move toward shore or remain there in spite of upwelling. We also found evidence of more passive advection and retention of pelagic juveniles of all sizes, including onshore movement during relaxation of upwelling. It appears that relaxation of upwelling may be a sufficient but not necessary aspect of the settlement of juvenile rockfish from pelagic to postpelagic habitats. If so, advection during upwelling may not have a negative effect on the settlement and ultimate recruitment of rockfish.