NEARSHORE ASSEMBLAGES OF LARVAL ROCKFISHES AND THEIR PHYSICAL-ENVIRONMENT OFF CENTRAL CALIFORNIA DURING AN EXTENDED EL-NINO EVENT, 1991-1993

Rockfish are among the most prevalent members of nearshore ichthyoplan kton assemblages off central California, yet their abundance varies gr eatly from year to year. Warm events, like El Nino, can have pronounce d effects on the success of a year class. We evaluate distribution, ab undance, and species composition of rockfish larvae on small spatial a nd temporal scales in the upwelling center north of Monterey Bay durin g an extended El Nino (December 1991 through June 1993) relative to re gional hydrography. Anomalously warm, low-salinity water to depths gre ater than 50 m during much of our study was indicative of an onshore d isplacement of the California Current; Upwelling was reduced and delay ed relative to other years. The two years differed, however, in the in tensity, duration, frequency, and direction of wind events. Larval roc kfish abundance was similar in both years of the El Nino, peaking in e arly February, and was among the highest when compared with estimates from CalCOFI surveys off central California (1951-84). Using larval ag es, we determined that median birthdates of shortbelly rockfish were i n early- to mid-February both years. Growth rates of larval shortbelly rockfish did not differ among months or between years. Relative to 19 93, rockfish larvae were more abundant; and sizes of larval shortbelly were significantly greater at onshore stations in 1992. This coincide d with onshore advection of water during the onset of the El Nino, sug gesting retention of larvae nearshore. Initiation of upwelling in Marc h and April 1993 and fewer larvae at onshore stations are indicative o f greater offshore transport during the second year. Juvenile rockfish es were extremely rare in summer of 1992; in 1993 they were twenty tim es more abundant and larger. Surviving juvenile shortbelly rockfish we re born late during both years; upwelling occurred coincidentally duri ng this period in 1993 but not in 1992. We suggest that substantially higher survival and recruitment of juvenile rockfishes in 1993 was due to increased offshore transport and perhaps lower predation during th e larval stages.