46 



Fishery Bulletin 105(1) 



Temperature and sea level anomaly proved to be im- 

 portant correlates with year-class strength for juvenile 

 rockfishes. Of the three environmental variables ex- 

 amined, nearshore temperature and sea level anomaly 

 were significantly and negatively correlated with the 

 abundance of all three species. Moser et al. (2000) 

 reported a similar relationship, with reduced abun- 

 dance of larval bocaccio and cowcod during periods of 

 high temperature off southern California. Ralston and 

 Howard (1995) reported a negative correlation between 

 recruited juvenile blue and yellowtail rockfish year- 

 class strength and sea surface temperature in January 

 through March. Stephens et al. (1984) surmised that 

 warm water was the limiting factor in the low recruit- 

 ment of juvenile blue and olive rockfish during 1978-81 



-1 



10 



000 

 000 

 000 

 ,000 

 ,000 

 ,000 

 ,000 

 ,000 

 ,000 

 ,000 



-3 



-2 



-1 



1 2 



Log (index) 



Figure 5 



Year-specific catch-at-age data from commercial trawl-caught adult 

 yellowtail rockfish (Sebastes flavidus) from Bodega Bay, CA, and 

 the log-transformed annual abundance index for yellowtail rockfish. 

 (A) 1997 landings; (B) 1998 landings. Numbers represent the year 

 class of aged fish. The solid line represents predicted values from the 

 relationship of the catch-at-age data and the log-transformed index. 



off southern California. Ainley et al. (1993) determined 

 that sea level during February and sea surface tempera- 

 ture in March were negatively correlated with pelagic 

 rockfish abundance for the period of 1973-90 off central 

 California. 



Temperature affects the growth rates of rockfishes, 

 which, in turn, affects species abundance. Johnson 

 et al. (2001) determined that growth rates declined 

 during months of high temperatures for juveniles of 

 three rockfish species. However, Boehlert and Yoklavich 

 (1983) found increased growth rates forjuvenile black 

 rockfish with increased temperature in the laboratory, 

 except under starvation conditions. Therefore, reduc- 

 tion in growth rates may be due to lower prey avail- 

 ability during El Nino conditions (Mullin and Conversi, 

 1989). This lower growth rate of juvenile 

 rockfishes during periods of high tempera- 

 tures may lead to reduced survival and 

 lower year-class strength. 



Although growth can vary directly with 

 temperature, temperature may also have 

 an indirect effect on rockfish abundance. 

 Strong El Nifio events, associated with 

 unusually high water temperatures last- 

 ing from a few months to over a year, 

 have occurred off California in 1982-83, 

 1991-92, and 1997-98 (Fedorov and Phi- 

 lander, 2000; Rebstock, 2001). VenTresca 

 et al. (1995) observed reduced condition 

 factor and gonadal indices for blue rock- 

 fish during the 1983 and 1992 El Niiios 

 off central California when water tem- 

 peratures were elevated. These reduc- 

 tions could lead to fewer larvae being 

 produced and hence ultimately to a lower 

 abundance of juveniles. El Nifio events 

 can also lead to changes in the strength 

 and timing of the annual phytoplank- 

 ton bloom, both of which can reduce the 

 distribution and abundance of the zoo- 

 plankton on which the juvenile rockfishes 

 feed (Lenarz et al., 1995). This reduction 

 in food availability could lead to lower 

 growth or survival of the juvenile rock- 

 fishes. Keister et al. (2005) found sev- 

 eral warm-water species of euphausiids, 

 chaetognaths, and copepods in Oregon 

 waters during the 1997-98 El Nifio. Reb- 

 stock (2001) observed that during periods 

 of high temperatures in 1983, 1992, and 

 1998, the species richness of copepods 

 was lower than a 49-year average. Co- 

 pepods are a preferred prey item for ju- 

 venile rockfishes (Reilly et al., 1992). A 

 change in species richness may reflect 

 a change in species composition to less 

 desirable food sources (e.g., prey is less 

 nutritious or less available to young rock- 

 fishes). Although the exact mechanism 

 is not clear, we observed that the three 



