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Fishery Bulletin 94(4). 1996 



rockfish juveniles in 1992. The 1993 pelagic juveniles 

 were dominated by shortbelly, squarespot, half- 

 banded (S. semicinctus), and chilipepper (S. goodei) 

 rockfishes, in that order. All of these species can pro- 

 duce larvae relatively late in the season. 



Among the dominant species, only those shortbelly 

 rockfish larvae released late in the season (March 

 and April) were represented in the birthdate distri- 

 butions of juveniles collected in the summer of both 

 years of the El Nino. The few pelagic juvenile 

 shortbelly rockfishes collected in May-June during 

 the 1983 El Nino event also had late birthdates 

 (Woodbury and Ralston, 1991). It is clear that the 

 largest proportion of larval shortbelly rockfish pro- 

 duction, >65% occurring prior to March during both 

 years of the 1991-93 El Nino event, did not survive 

 until the juvenile surveys conducted during the sum- 

 mers of 1992 and 1993. Blue rockfishes, largely pro- 

 duced in January and February and ranked second 

 (1992) and third (1993) in larval catches, were not 

 collected at all during pelagic juvenile surveys in 

 May-July 1992 (56 midwater trawls; Loeb et al. 1 ), 

 and represented 0.5% (n=29 individuals) of the total 

 catch of pelagic juveniles in May— July 1993 (65 

 midwater trawls; Loeb et al. 1 ). Stripetail rockfish, 

 another species whose parturition period is restricted 

 to early in the year off central California (i.e. No- 

 vember-March with a peak in January [Wyllie 

 Echeverria, 1987]), was relatively abundant in the 

 plankton both years but rare in the pelagic juvenile 

 collections (<0.1 and 0.5 fish per trawl). 



In accordance with the results of the surveys by 

 Loeb et al., 1 subtidal observations along the central 

 coast made by California's Department of Fish and 

 Game Sportfish Project biologists indicated that few 

 juveniles of nearshore rockfish species recruited to 

 rocky and kelp canopy areas off the Monterey Pen- 

 insula during May-August 1992 (VenTresca 3 ). Low 

 abundance of pelagic juvenile rockfishes off central 

 California also was noted during May-June 1992 

 surveys conducted by scientists of the NMFS Tiburon 

 Laboratory (Lenarz et al., 1995; Ralston and Howard, 

 1995) and during previous El Nino events of 1983 

 and 1986 (Wyllie Echeverria et al., 1990). In contrast, 

 overall abundance of pelagic juvenile rockfishes in 

 1993 was fourth greatest among the past eight years 

 of NMFS-Tiburon surveys (Lenarz et al., 1995), and 

 relatively high numbers, dominated by blue rock- 

 fishes, settled off Monterey during June-September 

 1993 (VenTresca 3 ). Substantially greater abundance 

 and larger sizes of pelagic juvenile rockfishes during 



3 VenTresca, D. 199. r >. California Department of Kish and 

 Game, 20 Lower Ragsdale Dr., No. 100, Monterey, CA 

 93940. Unpubl. data. 



May-July 1993 indicated that recruitment was likely 

 related to the timing of optimal environmental con- 

 ditions during larval development. This is consistent 

 with the dome-shaped relationship described by 

 Ralston and Howard (1995) between interannual 

 variability in winter SST's and estimates of year-class 

 strength for blue and yellowtail rockfishes off cen- 

 tral California collected from 1983 to 1992 (e.g. juve- 

 nile abundance was lowest when SST's were either 

 exceptionally low or high during winter months of 

 larval production). 



Mortality of fishes during the larval stage has been 

 attributed to starvation and predation; debate con- 

 tinues as to which factor is more significant for suc- 

 cessful recruitment (Hunter, 1981; Bailey and Houde, 

 1989). There was no evidence from our ichthyo- 

 plankton samples that suggested that young rock- 

 fishes were starving in either year of the El Nino 

 event. Growth of young shortbelly rockfishes was 

 similar throughout the parturition period, no differ- 

 ences were detected between the two years, and 

 growth in 1992-93 was similar to that estimated for 

 this species from the central California during non- 

 El Nino years (i.e. in 1989 [Laidig et al., 1991] and 

 in 1991 [Ralston et al., 1996]). Moreover, blue rock- 

 fish, although relatively common in the ichthyo- 

 plankton, abruptly disappeared at young ages (i.e. 

 when many were still dependent on yolk reserves) 

 from samples collected in late January and early 

 February and had very poor recruitment to the pe- 

 lagic juvenile stage in 1992. This finding suggests acute 

 mortality, perhaps coincident with onshore transport 

 and increased encounter rates with predators. 



Time of release of rockfish larvae can contribute 

 to variation in year-class abundance by influencing 

 the spatial and temporal coincidence of larvae, prey 

 availability, predator abundance, and favorable en- 

 vironmental conditions, such as temperature, up- 

 welling, and transport (Parrish et al., 1981; Methot, 

 1983; Checkley et al., 1988; Nyman and Conover, 

 1988). Rockfish larvae were more abundant and the 

 dominant species (shortbelly rockfish) was signifi- 

 cantly larger at onshore stations in 1992 than in 

 1993, indicating retention of larvae nearshore dur- 

 ing the first year of the El Nino event. These occur- 

 rences coincided with onshore advection of water, as 

 characterized by reversals in wind direction and by 

 warmer, less saline water that occurred during peak 

 larval rockfish abundance in February 1992. 



Larval retention in nearshore areas could be re- 

 sponsible for heavy mortality, possibly through in- 

 creased predation. Significant changes in zooplank- 

 ton assemblages associated with wind relaxation and 

 subsequent onshore transport have been noted along 

 central California (Farrell et al., 1991), and abun- 



