FISHERY BULLETIN, VOL. 72, NO. 1 



Sensitivity of Results to Errors in Estimates of 

 Natural Mortality 



Size-specific values of F were estimated using 

 values of M of 0.6 and 1.0 and an initial value of 

 F = 0.2. The results are compared to size-s])ecific 

 F when M = 0.8 in Figure 16. Although the 

 absolute values differ considerably, the same 

 general trends appear in each curve. The ratio 

 of FIM varies about threefold. 



Results of yield-per-recruit calculations are 

 shown in Tables 8 and 9 and Figures 17 and 18. 

 There is a steeper horizontal gradient when 

 M = 1.0 and a steeper vertical gradient when 

 M = 0.6 than when M = 0.8. That is, yield per 

 recruit is more sensitive to changes in effort 



40 



60 



80 100 120 140 



FORK LENGTH (cm.) 



160 



180 



Figure 16. — Estimates of size-specific F when its initial 

 value is 0.2 and using values for M of 0.6, 0.8, and 1 .0. 



Table 8. — Esliniales of yield per recruit (kg) for the entire fishery when M = 0.6, initial F = 0.2, and growth 



curve of LeGuen and Sakagawa (1973) is used. 



Table 9. — Estimates of yield per recruit (kg) for the entire fishery when M = 1.0, initial F 



curve of LeGuen and Sakagawa ( 1973) is used. 



0.2, and growth 



56 



