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Fishery Bulletin 100(4) 



equivalent of 14 hours of trawling with two nets and with 

 14-fathom (25.48 m) headropes at a speed of 3.2 knots (5.9 

 krn/h) (Bishop and Sterling. 1999). 



The estimate of the total amount removed for a species 

 within the whole fishery was calculated by summing the 

 removal estimates for the bioregions. This estimate was 

 then converted to a proportion of the estimated total bio- 

 mass of the species. 



An estimate of the total biomass of each species in the 

 bioregions where tiger prawn trawling occurs was gener- 

 ated from all research and scientific observer surveys 

 conducted in the NPF during the 1990s (Fig. 1, Table 1). 

 The gears used were prawn trawls (Florida flyer nets) and 

 two types offish trawls (Frank and Bryce trawls and Engel 

 trawls). Both night and daytime trawling were undertaken. 



Both prawn-trawl and fish-trawl surveys were analyzed in 

 order to cover the management area of the fishery. 



The catch rates of species in each trawl were converted 

 to the catch per swept area of the trawl as described previ- 

 ously. The fish trawls were assumed to have a spread of 0.6 

 of the headrope length (Blaber et al., 1994). A mean catch 

 rate for each gear at each time (day or night) was calcu- 

 lated in each bioregion, resulting in up to six catch rate 

 estimates for a species in a bioregion. The highest of these 

 means was used for each species in that bioregion. This 

 catch rate was then multiplied by the area of the bioregion 

 to give an estimate of total numbers of individuals in the 

 bioregion. Currently there are no robust estimates of the 

 catchability coefficients for the various trawl gears and 

 therefore a catchability coefficient of one was assumed for 



