Yoklavich et al.: Larval rockfishes and their physical environment off central California 



767 



plankton assemblages, especially off central Califor- 

 nia, annual abundance varies widely (Moser and 

 Boehlert, 1991; Moser et al., 1993). Factors affecting 

 survival of young fishes, including hydrographic con- 

 ditions and associated transport processes, density of 

 prey and predators, and spawning seasonality are po- 

 tentially critical determinants of rockfish recruitment. 



Rockfishes are viviparous, with larval release (par- 

 turition) occurring mainly from January to April for 

 many of the species off central California (Wyllie 

 Echeverria, 1987), just before and during the onset 

 of upwelling. Duration of the pelagic larval and ju- 

 venile stages of many species is typically several 

 months (Anderson, 1983; Woodbury and Ralston, 

 1991) but may be up to one year (Boehlert, 1977). 

 The arrival and subsequent settlement of pelagic 

 juvenile rockfishes in subtidal areas off central Cali- 

 fornia may be associated with upwelling events and 

 onshore transport during periods of wind relaxation 

 (VenTresca et al., 1990; Larson et al., 1994). The re- 

 curring bifurcated plumes of upwelled water off Pt. 

 Ano Nuevo, a relatively unfished area that could 

 serve as a source of larvae, interspersed with occa- 

 sional periods of wind relaxation and onshore trans- 

 port, may be important vehicles for transport of 

 young rockfishes from upwelling centers into 

 nearshore areas of Monterey Bay and farther south. 



Warm events, often indicative of an El Nino, occur 

 along the coast of California every 2-10 years ( Norton 

 et al., 1985) and persist for 1-3 years (Chelton et al., 

 1982). Strong events occurred coastwide in 1926, 

 1941, 1958, and 1983 (Ware, 1995). El Nino-like con- 

 ditions can include 1) increased sea-surface tempera- 

 ture (SST) and depth of thermocline; 2) positive sea- 

 level anomalies (Chelton and Davis, 1982); 3) reduced 

 upwelling, nutrients, and primary and secondary 

 production (Fiedler, 1984; McGowan, 1985; Miller et 

 al., 1985); and 4) increased poleward and onshore 

 flow of coastal water (Simpson, 1984; Hayward et 

 al., 1994; Lynn et al., 1995). Significant increases in 

 SST were noted off central California during win- 

 ters of 1972, 1976, 1979, and 1983, which corre- 

 sponded with El Nino episodes (Breaker et al., 1983). 



Warm events like, but not restricted to, El Nino 

 can have disastrous effects on year-class strength of 

 rockfishes, a group with arctic to temperate affini- 

 ties and distribution (Karpov et al., 1995; Lenarz et 

 al., 1995; Ralston and Howard, 1995). Anomalously 

 warm water and suppression of upwelling have been 

 associated with large-scale reductions in the primary 

 prey (e.g. euphausiids and smaller zooplankton) of 

 juvenile and adult rockfishes (Mullin and Conversi, 

 1989). Reduced prey abundance may negatively af- 

 fect the somatic and reproductive condition of adult 

 rockfish (Lenarz and Wyllie Echeverria, 1986; 



VenTresca et al., 1995), potentially disrupting the 

 timing, location, and net output of reproduction. 

 Changes in distribution and dispersal patterns of 

 pelagic larvae, and altered production of their prey 

 and predators, are expected during anomalous warm 

 events (Bailey and Incze, 1985; Brodeur et al., 1985). 

 In this paper we evaluate distribution, abundance, 

 and species composition of rockfish larvae and asso- 

 ciated hydrography on small spatial (<20 km) and 

 short temporal (biweekly to monthly) scales in an 

 upwelling center north of Monterey Bay during an 

 extended El Nino event (1991-93). From size, age, 

 and estimated growth models, we compare birthdate 

 distributions of early larvae and surviving pelagic 

 juveniles of the most common species. We discuss 

 potential larval transport and subsequent strength 

 and timing of juvenile recruitment to nearshore 

 areas along the central California coast. 



Methods 



Sampling 



Ichthyoplankton surveys were conducted during day- 

 time aboard the RV Ricketts (ca. 11 m long) at five 

 stations along a northeast-southwest transect off 

 Davenport, California (37°N, 122°10'W; Fig. 1). Sta- 



Figure 1 



Monterey Bay study area and five stations (solid dots) sampled 

 for larval fish off Davenport. Sites of wind measurements (46042) 

 and 1989-91 CTD casts (H3, CI, and Ql) are indicated. 



