766 



Abstract.— Rockfish are among the 

 most prevalent members of nearshore 

 ichthyoplankton assemblages off cen- 

 tral California, yet their abundance 

 varies greatly from year to year. Warm 

 events, like El Nino, can have pro- 

 nounced effects on the success of a year 

 class. We evaluate distribution, abun- 

 dance, and species composition of rock- 

 fish larvae on small spatial and tempo- 

 ral scales in the upwelling center north 

 of Monterey Bay during an extended El 

 Nino (December 1991 through June 

 1993) relative to regional hydrography. 



Anomalously warm, low-salinity wa- 

 ter to depths greater than 50 m during 

 much of our study was indicative of an 

 onshore displacement of the California 

 Current. Upwelling was reduced and 

 delayed relative to other years. The two 

 years differed, however, in the inten- 

 sity, duration, frequency, and direction 

 of wind events. Larval rockfish abun- 

 dance was similar in both years of the 

 El Nino, peaking in early February, and 

 was among the highest when compared 

 with estimates from CalCOFI surveys 

 off central California ( 1951-84). Using 

 larval ages, we determined that median 

 birthdates of shortbelly rockfish were 

 in early- to mid-February both years. 

 Growth rates of larval shortbelly rock- 

 fish did not differ among months or 

 between years. Relative to 1993, rock- 

 fish larvae were more abundant, and 

 sizes of larval shortbelly were signifi- 

 cantly greater at onshore stations in 

 1992. This coincided with onshore ad- 

 vection of water during the onset of the 

 El Nino, suggesting retention of larvae 

 nearshore. Initiation of upwelling in 

 March and April 1993 and fewer lar- 

 vae at onshore stations are indicative 

 of greater offshore transport during the 

 second year. 



Juvenile rockfishes were extremely 

 rare in summer of 1992; in 1993 they 

 were twenty times more abundant and 

 larger. Surviving juvenile shortbelly 

 rockfish were born late during both 

 years; upwelling occurred coinciden- 

 tally during this period in 1993 but not 

 in 1992. We suggest that substantially 

 higher survival and recruitment of ju- 

 venile rockfishes in 1993 was due to in- 

 creased offshore transport and perhaps 

 lower predation during the larval stages 



Nearshore assemblages of larval 

 rockfishes and their physical 

 environment off central California 

 during an extended El Nino event, 

 1991-1993 



Mary M. Yoklavich 



Pacific Fisheries Environmental Group, Southwest Fisheries Science Center 



National Marine Fisheries Service, NOAA 



1352 Lighthouse Avenue, Pacific Grove, California 93950-2097 



e-mail address. myoklavich@pfeg noaa.gov 



Valerie J. Loeb 

 Mary Nishimoto 

 Brendan Daly 



Moss Landing Marine Laboratories 



PO Box 450, Moss Landing, California 95039 



Manuscript accepted 26 June 1996. 

 Fishery' Bulletin 94:766-782 (1996) 



Ocean conditions off central Califor- 

 nia are influenced seasonally by a 

 variety of factors and processes that 

 operate on a local scale (e.g. wind, 

 upwelling, freshwater input, and 

 bathymetry) and larger spatial 

 scales (e.g. the California Current 

 System and El Nino events). Pre- 

 vailing winds from the northwest 

 produce relatively intense up- 

 welling, particularly near capes and 

 headlands, typically during March 

 through September (Kelly, 1985; 

 Breaker and Broenkow, 1994; Rosen- 

 feld et al., 1994a). An abrupt decrease 

 in sea-surface temperature, occur- 

 ring sometime between February 

 and May, defines the spring transi- 

 tion to coastal upwelling, which is 

 associated with increased nutrient 

 concentration, primary production, 

 and offshore transport of surface 

 water. Because the coastal ocean 

 environment can respond rapidly to 

 changes in local wind speed, direc- 

 tion, and duration, onshore trans- 

 port of water off central California 

 can occur during periods of reduced 

 equatorward winds and subsequent 

 cessation of upwelling (Broenkow 



and Smethie, 1978; Rosenfeld et al., 

 1994a). This transport is mani- 

 fested nearshore by the occurrence 

 of warm, relatively low salinity wa- 

 ter representative of the offshore 

 core of the California Current. 



PointAhoNuevo(37.1°N, 1'22.3°W), 

 to the north of Monterey Bay, has 

 been identified as a distinct center 

 of upwelling, associated with bifur- 

 cated plumes of cool, saline, nutri- 

 ent-rich surface water that are ad- 

 verted both seaward and southward 

 across Monterey Bay (Tracy, 1990; 

 Schwing et al., 1991; Rosenfeld et 

 al., 1994a). According to satellite 

 and in situ data, these recurrent 

 upwelling plumes can extend 10- 

 100 km offshore and persist from 

 days to weeks. As it flows equator- 

 ward, some of this upwelled water 

 is advected into the bay. 



Rockfishes (Sebastes spp.) are tre- 

 mendously diverse, dominate coastal 

 benthic fish assemblages and sup- 

 port heavily exploited recreational 

 and commercial fisheries in Califor- 

 nia (Lea, 1992). Although rockfish 

 larvae are among the most preva- 

 lent members of nearshore ichthyo- 



