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Fishery Bulletin 100(4) 



sharks and rays, particularly the smaller individuals, die 

 within the trawl net (56'^'^). The lower sui-vival rates of 

 male individuals is possibly because the males of most elas- 

 mobranch species are smaller than the females. The rhyn- 

 chobatid R. djiddensis had a higher survival rate {90'^7r) 

 than most other species, whereas the lowest survival rate 

 was seen in C. tilstoni and R. acutus (18%). Although the 

 larger elasmobranchs appeared to have a higher within- 

 net survival, in the commercial fishery these were the very 

 individuals killed for their fins and therefore their mortal- 

 ity was ultimately higher than that predicted by their size 

 alone. In 2001 the NPF introduced an industry-initiated 

 ban on all shark products, so that the only mortality these 

 species are subject to is that caused by the capture process. 



Differences between species in survival rates may influ- 

 ence changes in the relative abundance of species. 



Assessment of the sustainability of 

 elasmobranch species 



Elasmobranchs, in general, are more susceptible to over- 

 fishing than are bony fishes, but there is likely to be a 

 range of sensitivities among the species (Walker. 1998; 

 Stevens et al., 2000). The process we applied in our study 

 allowed us to examine these different sensitivities and 

 to highlight those species whose populations were most 

 likely to be affected by the NPF. The process was designed 

 to deal with the high diversity of the bycatch and the 



