Grandcourt: Effect of intensive line fisfiing on biomass of Pristipomoides ftlamentosus 



309 



12 3 4 



5 6 7 8 9 10 11 12 13 



Day number 



Figure 3 



Reduction in the biomass of Pristipomoides filamentosus over the fishing 

 period at Saya de Malha Bank. Line shows the exponential model; v = 

 72.972 e-'39'' fitted to the data (r2=0.994). 



of 43.633 (±4.538 SE) kg/man hour gave an initial biomass 

 estimate of 72,582 kg for P. filamentosus accessible to a line 

 fishery at the study site. Bootstrapped upper and lower 

 95% confidence limits for the initial biomass estimate were 

 62,750 and 91,376 kg, respectively. Analysis of the daily 

 estimates showed that there was an exponential decrease 

 in remaining biomass over the fishing period (Fig. 3). The 

 biomass densities, potential yield estimates, and respective 

 959c confidence intervals are given in Table 3. 



Mees (1993) derived a maximum sustainable yield es- 

 timate of 24% for the virgin biomass of P filamentosus on 

 the edge of the Seychelles Bank using the method of Bed- 

 dington and Cooke (1983). 



Applying this proportion to the initial biomass for 

 P. filamentosus on the north western promontory of Saya de 

 Malha Bank gives an annual maximum sustainable yield 

 estimate of 17.4 t. The quantity of P. filamentosus caught 

 by the mothership-dory fishing operation represented 82% 

 of the initial virgin biomass available to a hook-and-line 

 fishery. The amount removed was equivalent to more than 

 three times the estimated annual maximum sustainable 

 yield. 



Discussion 



The fisheries resources of Saya de Malha Bank have been 

 exploited by Mauritian mothership-dory fishing operations 

 since the late 1960s. 



However, the fisheries operate only to a maximum 

 depth of 50 m, and a single species (Lethrinus mahsena) 

 constitutes 80-90% of the catch (Mees^). The exploitation of 



P. filamentosus had not occurred prior to the present study 

 because of the belief that the fish were ciguatoxic (Samboo 

 and Mauree, 1987), and consequently the population re- 

 mained in a virgin state. 



The Leslie constant catchability model assumes that the 

 population is completely closed, i.e. there is no recruitment, 

 growth, natural mortality, immigration or emigration dur- 

 ing the time frame of the data to which it is applied. Natu- 

 ral mortality, recruitment, and growth can be assumed to 



2 Mees, C. C. 1996. Management of multi-species tropical 

 fisheries, 193 p. Marine Resources Assessment Group Ltd., 47 

 Princes Gate, London SW7 2QA, UK. 



