Laidig et al : Relationship between abundance of juvenile Sebostes spp, and environmental variables 



45 



species of rockfishes in our study. The abundance of all 

 three species were significantly and negatively correlat- 

 ed with sea level anomaly and nearshore temperature 

 during this time period. Ralston and Howard (1995) 

 also argued that year-class strength was set in the lar- 

 val period for rockfishes with winter parturition. They 

 analyzed data from midwater trawls in May and June 

 and compared them with data from nearshore surveys 

 in summer. Because there was a strong correlation be- 

 tween the two data sets, they postulated that the year- 

 class was set earlier in the year than May, probably 

 during the larval stage. VenTresca et al.^ also reported 

 evidence of the establishment of year-class strength in 

 the larval stage. In 1992, they found large concentra- 

 tions of larval rockfishes in January, but three to four 

 months later very few juveniles appeared in midwater 

 trawls. They surmised that the El Nino conditions of 

 elevated water temperatures and reduced upwelling 

 resulted in poor survival. 



Synchrony in juvenile abundance among rockfish spe- 

 cies has been observed in other studies. Ralston and 

 Howard (1995) ascertained that trends in abundance 

 for juvenile blue and yellowtail rockfish from midwater 

 trawls were highly correlated over the 10 years of their 



study. Ammann (2001) discovered a comparable pattern 

 in recruitment of juvenile yellowtail and black rockfish 

 to the kelp bed environment in 1999 and 2000. Ste- 

 phens et al. (1984) reported that juvenile abundance of 

 both blue and olive rockfish (S. serranoides), dropped to 

 virtually zero during the years 1978-81. In our study, 

 blue, yellowtail, and black rockfish covaried over a pe- 

 riod of 21 years. 



Although offshore Ekman transport, or upwelling, has 

 been suggested as a predictor of year-class strength, we 

 found it to have little correlation with the abundance of 

 juvenile rockfishes from northern California. Maximum 

 upwelling off the central California coast occurs in late 

 spring and summer (Rosenfeld et al., 1994; Yoklavich 

 et al., 1996). This upwelling occurred after the larval 

 period for winter-spawning Sebastes spp., and therefore 

 after the timing of year-class determination. Larson 

 et al. (1994) found that larger pelagic juveniles were 

 often close to shore even when upwelling was strong, 

 indicating that later-stage pelagic juveniles were not 

 directly affected by upwelling. If water movement on- 

 shore and offshore influences the population size of 

 juvenile rockfishes, perhaps this effect occurs during 

 the early stages. 



