484 



Fishery Bulletin 92(3). 1994 



(1988). However, for years not available from Strub 

 and James, it was estimated from weekly upwelling 

 indices (at 45°N 125°W, Bakun, 1975; Mason and 

 Bakun, 1986). In the latter case the time of spring 

 transition was assigned to the first week of the year 

 in which the weekly upwelling index became posi- 

 tive and remained positive for at least another week. 

 The spring transition dates reported by Strub and 

 James (1988) were highly correlated with our esti- 

 mates (r=0.80; P<0.01). Because March is usually a 

 month of predominant onshore Ekman transport 

 prior to the spring transition (i.e. negative offshore 

 Ekman transport), we determined whether YCS 

 variation was correlated with mean onshore Ekman 

 transport during March. 



referred to as original series), unrelated trends in 

 original series often cause spurious correlations and 

 conceal the extent of year-to-year associations 

 (Dickey et al., 1986; Norton 7 ; Cohen et al., 1991). 

 Therefore, first-order differencing was used to evalu- 

 ate the reliability of correlations based on the origi- 

 nal series (Chatfield, 1989; here after referred to as 

 filtered series). By this criterion, a significant corre- 

 lation for original series was deemed reliable only if 

 the attendant correlation for the filtered series had 

 the same correlation sign and a minimum absolute 

 value (I r\ > 0.10). Although this procedure does not 

 account for P-values of filtered series, it provides a 

 more consistent selection of factors potentially asso- 

 ciated with recruitment variation. 



Analytical methods 



Spearman's correlation analyses (Tate and Clelland, 

 1957) were used to account for linear and nonlinear 

 monotonic associations between YCS and indepen- 

 dent variables (i.e. potential egg production, envi- 

 ronmental factors, and timing of the spring transi- 

 tion). Independent variables were lagged to the first 

 year of life of each cohort to determine potential in- 

 fluences on YCS at the time year classes were born. 

 Exploratory Spearman's correlation analyses were 

 used for each season of the year because of the sea- 

 sonality of different early life stages and environ- 

 mental factors (Fig. 2, Appendix A). 



Because many environmental-YCS relationships 

 showed anomalous correlations during the 1958 El 

 Nino, one of the largest El Nino events in the twen- 

 tieth century (Cannon et al., 1985), this year was 

 not included in Spearman's correlation analyses. 

 However, after the most consistent Spearman's cor- 

 relations for 1959-77 were established, all years from 

 1958 to 1977 were considered in regression analy- 

 ses. Such regressions consisted of estimated YCS on 

 environmental anomalies. These anomalies were 

 computed as the actual seasonal value of a given fac- 

 tor minus its long-term mean for 1958-77. The use 

 of anomalies as independent variables was justified 

 to reduce multicollinearity effects in polynomial re- 

 gressions (Neter et al., 1989). 



The Bonferroni correction and the P-value plot of 

 Schweder and Spjotvoll (1982) required individual 

 P-values =0.001 for an overall P-value = 0.05 in mul- 

 tiple comparisons between YCS and environmental 

 factors. Since such P-values would have made it dif- 

 ficult to detect meaningful ecological relationships, 

 significance of correlations was based on individual 

 P-values <0.05. Although statistical significance in 

 our study was based on nonfiltered data (here after 



Results 



Potential spawning biomass 



The effect of spawning biomass on subsequent re- 

 cruitment strength was minimal as indicated by simi- 

 lar variations from 1970 to 1977 in YCS per paren- 

 tal egg and the YCS index (Fig. 3). The initial de- 

 cline in YCS in the 1970s was not linked to a de- 



' Norton, J. 1990. Relationship between California Current 

 temperatures and intensity of the Aleutian Low. Southwest 

 Fisheries Science Center. Report of activities. March-April 1990. 

 La Jolla, CA, p. 16-18. 



