Grandcourt et al Biology and assessment of Diagiamma pictum and Lethnnus nebulosus in the southern Arabian Gulf 



81 



2000 



1500 



1000 



500 



n = 5006 



1 2 3 4 5 6 7 8 9 10 11 12 13 



2000  



1500 



1000 



500 



n = 13.129 



1 2 3 4 5 6 7 8 9 10 11 12 13 14 

 Age group (yr) 



Figure 6 



Age-frequency distributions for I A) Diagramma pictum 

 and (Bi Lethrinus nebulosus derived from age-length 

 keys and size-frequency data. 



to the fishery at a mean size iLc^g) which was smaller 

 than the mean size at which first sexual maturity was 

 attained (L,„j,(). 



Assessment of the fishery 



The size at which yield per recruit would be maximized 

 *-^max' w^s ■^4.4 cm (Lp) for D. pictum and 36.9 cm (Lp) 

 for L. nebulosus. For both species, these values were 

 considerably greater than the mean size at first capture 

 and the mean size at first sexual maturity (Fig. 9). 



The exploitation rate for D. pictum (0.79/yrl was 

 greater than that which would maximize yield per re- 

 cruit (0.57/yr) at the existing mean size at first capture 

 (Table 6). Furthermore, the same yield per recruit could 

 be achieved at a much lower exploitation rate and at 

 an increased relative biomass per recruit (Fig. 10). 

 The yield-per-recruit function also indicated that an 

 increase in the size at first capture to that which would 



Table 5 



Probability of capture ( selectivity) for Diagramma pictum 

 and Lethrinus nebulosus. 



Probability of capture 



50% (L50) 



