Stobutzkl et a\ Sustainabillty of elasmobranchs caught as bycatch in a tropical prawn trawl fishery 



801 



129° 



1 



134° 



139°E 



Northern Prawn 

 Fishery management 

 area 



229,974 



1 5 "S 



Figure 1 



The management area of the northern prawn fishery (NPFl and the bioregions defined through the 

 interim marine and coastal rationalization (IMCR) process (Thackway and Cresswell. 1998). The shaded 

 area represents the regions fished by commercial prawn trawlers. The dots mark the positions of the 

 trawls that were sampled to estimate the removal rates and total biomass of bycatch species (Table 1). 

 The numbers refer to the bioregions (l=Oceanic Shoals, 2=Tiwi, 3=Cobourg, 4=Arnhem Wessel, 5= 

 Arafura, 6=Groote, 7=Pellew, 8=Wellesley, 9=Karumba-Nassau, 10=West Cape York, ll=Carpentaria). 



This study is one of several (Milton, 2001; Stobutzki 

 et al. , 2001a) that broadly examine the sustainabillty of 

 bycatch species groups in the NPF. The aim of this study 

 was to assess the relative sustainabillty of elasmobranch 

 species taken as bycatch in the NPF. We use a broadbrush 

 method developed by Stobutzki et al (2001a) to encompass 

 the high diversity of and limited amount of information. 

 This semiquantitative technique assesses the sustainabil- 

 lty of species according to two overriding characteristics: 

 1) their susceptibility to capture and mortality due to 

 trawling; and 2) the ability of a population to recover after 

 depletion. Traditional population assessment methods 

 have attempted to measure or model these factors. The 

 broadbrush method uses biological and ecological criteria 

 to rank species with respect to these two characteristics, 

 maximizing the use of the limited information available. 

 The method identifies species that are least likely to be 

 sustainable in the bycatch, so that these can be the focus 

 of further research and management. 



Methods 



Species present in the NPF and 

 those captured as bycatch 



A Hst of the elasmobranchs species recorded in the area 

 of the NPF was compiled from Last and Stevens (1994). 



A list of species taken as NPF bycatch has been collated 

 from two sources: 1) fishery research surveys undertaken 

 within the NPF fishing grounds (Crocos and Coman, 1997; 

 Stobutzki et al., 2001b; Blaber et al.^; Crocos et al.'^); and 

 2 ) records of elasmobranch bycatch by observers on com- 

 mercial vessels (these observers were either scientific 

 staff or trained crew-members) (Stobutzki, 2001b; Pender 

 etal.^; Stobutzki etal. 5). 



 Blaber, S., D. Brewer, C. Burridge, M. Farmer, D. Milton. J. Salini, 

 Y-G. Wang, T. Wassenberg, C. Buxton, I. Cartwright, S. Eayrs, N. 

 Rawlinson, R. Buckworth, N. Gill, J. MacCartie. R. Mounsey, 

 and D. Ramm. 1997. Effects of trawl design on bycatch and 

 benthos m prawn and finfish fisheries. Final report to Fisher- 

 ies Research and Development Corporation (FRDC), Project 

 93/179, 190 p. FRDC, PO Box 222, Deakm West ACT 2600, 

 Australia. 



' Crocos, P J., D. M. Smith, and G. Marsden. 1997. Factors 

 affecting the reproductive performance of captive and wild 

 broodstock prawns. Final report to the Fisheries Research and 

 Development Corporation (FRDC I. Project 92/51, 87 p. FRDC, 

 PO Box 222, Deakin West ACT 2600, Australia. 

 Pender, P J., R. S. Willing, and D. C. Ramm. 1992. Northern 

 prawn fishery bycatch study: distribution, abundance, size and 

 use of bycatch from the mixed species fishery. Northern Terri- 

 torv Department of Primary Industry and Fisheries ( NT DPIF). 

 fishery report 26, 97 p. NT DPIF, GPO Box 3000, Darwin NT 

 0801, Australia. 



' See next page for footnote 5. 



