Ralston et al : An approach to estimating rockfish biomass from larval production 



143 



80000 



_ 75000 - 



E 70000 - 



^ 65000 



60000 



55000 I I I I I I ...■ I I I I I I 



010 015 020 0.25 0.30 35 

 Natural mortality rate (/yr) 



040 



Figure 14 



Sensitivity of the larval production estimate of shortbelly 

 rockfish total biomass to the estimated natural morality 

 rate. Vertical dashed lines extending up from the abscissa 

 encompass the likely range of shortbelly rockfish natural 

 mortality (Pearson et al., 1991). 



150 n 



Cruise Date 



18 20 22 24 26 28 30 32 34 36 38 40 42 44 46 

 Mean calendar date of spawning distribution 



Figure IS 



Sensitivity of the total biomass estimate to the mean of the seasonal distri- 

 bution of shortbelly rockfish larval production, based on CalCOFI samples 

 collected at station 63.55. The estimated mean (//„=32.62) is represented by 

 the square, which is bounded by its 95'7r confidence interval. The effect of mis- 

 specifying//,, over a broader range (i.e. ±2 weeks) is also shown. 



fully consider sources of error and uncertainty in the lar- 

 val production estimate. 



Results presented in Table 2 show that errors in esti- 

 mating the six growth curve parameters had negligible 

 effects on the biomass estimate, ranging at most from 

 -2.05% to -(-2.01'7f. However, estimation errors in the 



logarithmically transformed power function regression 

 of fecundity on weight had a considerably greater effect. 

 Parameter perturbations in this function altered biomass 

 estimates by ~15-20'X(. In contrast, errors in estimating 

 the parameters of the logistic maturity ogive had virtually 

 no effect. 



