82 



Fishery Bulletin 104(1) 



• Length converted 



* Age based 



7 

 6 



5 - 



t 



4  



3 



2 



1 



B 



»oo' 



10 12 14 16 



• Length converted 

 A Age based 



5 10 15 20 



Age (yr)- Relative age (yr) 



25 



Figure 7 



Age-based catch curves (InF against A^e) and length- 

 converted catch curves (In F/dt against Relative age) 

 for Diagramma pictum (A) and Lethrinus nebulosus (B). 

 Dashed and solid lines show the regression equation 

 {y = b.x+a) fitted to data for age-based and length-con- 

 verted catch curves, respectively. Only solid points are 

 included in the regressions. 



10 20 30 



50 



60 



70 



B 



30 40 50 



Fork length (cm) 



60 



70 



Figure 8 



Selectivity curves for (A) Diagramma pictum and (B) 

 Lethrinus nebulosus, showing the mean size at first 

 capture at probabilities of 0.5 (^5,,), 0.75 (L-5). and the 

 size at which fish are fully recruited to the fishery <Lj(„,). 



maximize yield per recruit would be associated with 

 a substantial increase in yield at the current level of 

 exploitation. An increase in the size at first capture to 

 that at which sexual maturity occurs (L^^^) was also 

 predicted to be associated with an increase in yield, 

 although to a lesser degree (Fig. 10). 



The relative biomass per recruit for D. pictum at 

 the current exploitation rate was less than 10% of 

 that at the theoretical unexploited level. An increase 

 in the mean size at first capture to that which would 

 maximize yield per recruit was predicted to be asso- 

 ciated with a small increase in biomass per recruit. 

 Changes in the exploitation rate were predicted to 

 have a greater impact on biomass per recruit, which 

 was estimated to be above 50% of the unexploited 

 level at the optimum exploitation rate (£„„,) (Table 7). 



