Stobutzki et aL: Suslainability of elasmobranchs caught as bycatch In a tropical prawn trawl fishery 



813 



Low 3 



High 1 



3 

 High 



Figure 2 



The ranking of elasniobranch species with respect to criteria that reflect their 

 susceptibiHty to capture and mortahty due to prawn trawhng and their capacity 

 to recover after depletion by trawling. These factors combine to reflect the rela- 

 tive ability of species to sustain capture as prawn trawl bycatch in the northern 

 prawn fishery and therefore their relative priority with respect to research and 

 management. Numbers refer to species combinations that fall together on the 

 graph. ( l=Hj, Pm, Pz; 2=Ca, Cle, Dt, Gsa, Ssa, Tm; 3=Af. Dsa, Hf Hg Hua. Oo, 

 Rty, Ua; 4=Cf Aa; 5=Ana, Cli; 6=Rac, He). Explanations of the abbreviations for 

 species are given in Table 3. 



paucity of information available for most species. Our pro- 

 cess was similar to that used by the International Union 

 for the Conservation of Nature and Natural Resources 

 iIUCN) red lists (lUCN. 1995) that categorize species with 

 respect to the threat of extinction worldwide. The lUCN 

 uses criteria on the extent of population decrease, area of 

 occurrence, percentage of population that is mature, and 

 the probability of extinction (lUCN, 1995). The lUCN cri- 

 teria have been modified for application to marine fishes 

 and to smaller geographic scales (Musick, 1998). With 

 respect to elasmobranchs, several authors have exam- 

 ined the variable resilience of species to fishing pressure. 

 These approaches have focused on life history character- 

 istics that influence the recovery of populations, including 

 reproductive and growth parameters ( reviewed by Stevens 

 et al., 2000). Our process is similar to these but focuses at 

 the level of an individual fishery, incorporating fishery- 

 specific information on the susceptibility of species to the 

 fishery. Of significant importance with all methods is the 

 ability to calculate the range of parameters required for a 

 large number of species (Stevens et al., 2000). The semi- 



quantitative method used in our study maximizes what 

 can be determined from the data available and enables 

 consistency across the species. The criteria include char- 

 acteristics that influence the probability of extinction of a 

 species and its sensitivity to overfishing (McKjnney, 1997: 

 Carlton et al, 1999; Roberts and Hawkins, 1999; Stevens 

 et al., 2000). Our analysis provides a process for highlight- 

 ing gaps in information and for prioritizing species for 

 future management and research. This process does not 

 replace traditional methods of population assessment but 

 provides a rapid assessment of the species, so that tradi- 

 tional methods can be focused on the high-risk species. 



The species that were least likely to be sustainable in 

 the bycatch of the NPF were D. brevicaudatus. P. pecti- 

 nata, P. clavata, P. microdon, P. zijsron, and Himantura 

 Jenkinsii (Fig. 3). The pristids and H.jenkinsii had ranks 

 of 1 on the susceptibility axis, the lowest possible rank, 

 and D. brevicaudatus ranked 1.15 (Appendix 1). These 

 species are demersal, are rare in the bycatch, and at least 

 for the pristids (which have restricted depth distributions) 

 are likely to be rare. Nothing is known about their sur- 



