Hannah: A new method for indexing spawning stock and recruitment for Pandalus /ordani 



487 



(Fig. 3), The linear regression model (Table 2; model 

 1) was highly significant, with April SLH explaining 

 48*7?^ (unadjusted for degrees of freedom, unless noted) 

 of the variation in log recruits. More importantly, the 

 linear relationship is not based heavily on just a few 

 points but appears quite general in nature, confirm- 

 ing a routine relationship between recruitment and 

 April SLH shortly after the peak of larval release. 



The residuals from the regression of log recruits 

 on April SLH, graphed against the spawner index, 

 show a pattern that is suggestive of a quasilinear 

 stock-recruitment relationship, with the 1990 year 

 class as an exceptional outlier (Fig. 4). The same re- 

 siduals regressed against the egg production index 

 show a similar pattern (Fig. 5). The time series of 

 recruitment and the April catch of egg-bearing 

 shrimp from the year of larval release (Fig. 2) shows 

 that the year class released in 1989 ( 1990 year class) 

 may have been heavily impacted by the trawl fish- 

 ery, owing to an extremely high harvest of late egg- 

 bearing shrimp. This occurred in combination with 

 a high April sea level, suggestive of a late spring tran- 

 sition (Table 1). Data on the percentage of ovigerous 

 females in the April catch (Fig. 6) suggest that post- 

 ponement of the opening of the season to April 20'^ 

 each year could eliminate this impact. 



205 210 215 220 225 230 235 

 April sea level at Crescent City (cm) 



Figure 3 



Linear regression of the natural log of the 

 shrimp recruitment index, calculated assum- 

 ing elemental trawl efficiency of 0.50, versus 

 mean sea level height at Crescent City, Cali- 

 fornia, during April of the year of larval release. 



When the 1990 year class was excluded, neither 

 scatter graph (Figs, 4-5 ) exhibited sufficient evidence 

 of curvature to indicate the most appropriate form 



