Ralston and Howard: Year-class strength and cohort variability in Sebastes mystinus and S flavidus 



715 



Table 1 



Coefficients of variation in rockfish year-class strength at selected life 

 history stages. All pelagic and settled juvenile results are based on this 

 study. Within-year measurement error ( o" f ) removed for egg, pelagic 

 juvenile, and settled juvenile life history stages (see Methods section). 



Young-of-the-year 



Species 



Egg 



Pelagic 

 juvenile 



Settled 

 juvenile 



Entry to 

 fishery 



Sebastes mystinus 

 Sebastes flavidus 

 Sebastes entomelas 

 Sebastes goodei 

 Sebastes paucispinis 



0.10' 



1.98 

 1.19 

 2.25 

 1.49 

 0.96 



3.06-3.68 

 2.59-2.69 



0.60-0.87 

 0.82 3 

 1.39* 

 0.72 5 



' Eldridge and Jarvis (1995). 



2 Tagart (Footnote 2 in the text). 



3 Rogers and Lenarz. 1993. Status of the widow rockfish stock in 

 1993, Appendix B. In Appendices to the status of the Pacific Coast 

 groundfish fishery through 1993 and recommended acceptable bio- 

 logical catches for 1994. Pacific Fishery Management Council, 2000 

 SW First Ave., Suite 420, Portland, OR. 



4 Rogers and Bence. 1993. Status of the chilipepper rockfish stock in 

 1993, Appendix D. In Appendices to the status of the Pacific Coast 

 groundfish fishery through 1993 and recommended acceptable bio- 

 logical catches for 1994. Pacific Fishery Management Council, 2000 

 SW First Ave., Suite 420, Portland, OR. 



5 Bence and Rogers. 1992. Status of bocaccio in the Conception/ 

 Monterey/Eureka INPFC areas in 1992 and recommendations for 

 management in 1993, Appendix B. In Appendices to the status of 

 the Pacific Coast groundfish fishery through 1992 and recommended 

 acceptable biological catches for 1993. Pacific Fishery Management 

 Council, 2000 SW First Ave., Suite 420, Portland, OR. 



from 3.06 to 3.68 for blue rockfish and from 2.59 to 

 2.69 for yellowtail rockfish. The observational data 

 also indicated that 1985, 1987, 1988, and perhaps 



1991, were relatively strong years, whereas 1983, 



1992, and to some extent 1986, were weak years. 

 There were highly significant correlations between 



direct observation counts of settled juvenile rockfish 

 at Mendocino and Sonoma Counties. For blue rock- 

 fish the correlation was 0.925 (P<0.005) and for yel- 

 lowtail rockfish it was 0.887 (P<0.005). The greatest 

 disparity in abundance between these localities oc- 

 curred in 1991, when counts of the two species at 

 Mendocino County were low, both in comparison with 

 observations at Sonoma County and with catches in 

 the trawl survey. 



The time series of midwater trawl and direct ob- 

 servational data were also well correlated (Fig. 3). 

 For example, results for blue rockfish, Sebastes 

 mystinus, showed highly significant (P<0.005) posi- 

 tive correlations in excess of 0.80 at both the 

 Mendocino and Sonoma sites. Similarly, the correla- 

 tion between trawl survey estimates of yellowtail 

 rockfish, Sebastes flavidus, abundance and direct 



counts of this species at Sonoma County 

 (r=0.799) was significant (P<0.01). The 

 comparison between the trawl data and 

 Mendocino County counts (r=0.577) was 

 marginally insignificant (0.10<P<0.05). 

 Results were similar when comparisons 

 were restricted to the time period 1986- 

 92, i.e. when three repetitive sweeps of the 

 trawl survey area were completed each 

 year. 



Not only were trends in the abundance 

 of individual species at different study 

 sites well correlated; so too were the in- 

 terspecific abundance patterns of blue and 

 yellowtail rockfish at each of the three 

 specific study sites. For example, the time 

 series of blue rockfish abundance at the 

 Mendocino study site was highly corre- 

 lated with the yellowtail rockfish series at 

 the same site (r=0.961, P<0.001). At 

 Sonoma, variations in the abundance of 

 these two species was also closely linked 

 (r=0.906, P<0.001), substantially more so 

 than in the trawl data (r=0.589, P=0.073). 

 The substantial positive correlations 

 among the data for each species (Figs. 2 

 and 3) suggest that principal component 

 analysis (Green, 1978) would be effective 

 in extracting the primary interannual sig- 

 nal jointly evident in all three time series 

 (i.e. trawl, Mendocino, and Sonoma). In- 

 deed, results for blue rockfish show that 

 the first principal component alone accounted for 89% 

 of the variation present in the three data series. Like- 

 wise, for yellowtail rockfish the first component ac- 

 counted for 87% of the total variation. 



Winter SST's along the central California coast, 

 from Bodega Bay to Granite Canyon (Fig. 1), varied 

 greatly during the period 1983-92. Population mar- 

 ginal means for the year factor (y k ) in the ANOVA 

 temperature model ranged from a low of 10.6°C in 

 1989 to a high of 13.5°C in 1983, an El Nino year. 

 Typical winter SST's in the study region were 11.5- 

 12.0°C. For the two other factors in the model, the shore 

 station effect (oc ; ) showed that SSTs at Bodega Bay were 

 ~1.0°C cooler than at Southeast Farallon Island and at 

 Granite Canyon, which were quite similar to one an- 

 other. Likewise, the calendar date effect (/J.) showed 

 clearly the onset of spring transition to upwelling con- 

 ditions (Strub et al., 1987), evidenced by an abrupt cool- 

 ing trend that started in mid-March. 



Interannual variability in January-March SST's 

 appeared to be related to observed differences in the 

 abundance of pelagic juveniles captured by midwater 

 trawl during May-June and of settled juveniles ob- 



