Population biology and stock assessment of Pristipomoides filamentosus on the Mahe Plateau, Seychelles

Abstract

The population of P. filamentosus around the periphery of the Mahe Plateau was studied using data derived from commercial handline fishing operations between November 1989 and December 1990. Sex ratio was close to one. Fork length was in the range 25.6–79.8 cm: at first sexual maturity, 36–38 cm for females and 40–42 cm for males. Spawning occurred from October to April peaking between February and April and in November.The length (f.l., cm)–weight (kg) relationship was W=0.00005353 ×f.l.2.7004. The von Bertalanffy growth parameters, estimated from length frequency data, were K=0.2875 and Linf=81.7 cm. Mortality rates, estimated from length converted catch curve analysis, were Z=0.811, F=0.277 with M=0.534 derived from Pauly's empirical formula. Jones' length cohort analysis gave an estimate of F= 0.294 for the fully exploited part of the stock, and a density of 2.59 t km−2 for the periphery of the plateau from 75 to 150 m depth. The Lesley constant catchability model, applied to the results of intensive fishing around isolated banks, derived a mean density estimate of 2.99t km−2. The sustainable yield was estimated to be 233–268 tonnes per annum and the catch in 1990 was 200 tonnes.