Population parameters and exploitation rate of demersal fishes in Brunei Darussalam (1989–1990)

Abstract

Abstract Growth parameters ( L ∞ and K ) and mortality coefficients ( Z , M and F ) were estimated for 25 fish species caught in Brunei Darussalam. The number of recruitment peaks, growth performance index ( φ ′) and exploitation ratio ( E = F / Z ) was also assessed for each species. Routines in the FAO-ICLARM Stock Assessment Tools (FiSAT) software were used to estimate the parameters from length distribution data collected during a trawl survey in the coastal waters (10–100 m depth) of Brunei Darussalam from July 1989 to June 1990. The key parameters were used in yield- (Y/R) and biomass-per-recruit (B/R) analyses to derive reference points and evaluate the exploitation status of the 25 species. The E estimates for the 25 species were compared with those from other studies conducted in South and Southeast Asia to assess the relative exploitation status of demersal fish stocks in Brunei Darussalam. The other parameters obtained were also compared with available estimates to evaluate consistency of the results with current knowledge about the species in the region. The 25 species studied represented 70% of demersal abundance off Brunei Darussalam during the 1989–1990 survey. Relatively high K (and low L ∞ ) values, typical of short-lived tropical fishes, were obtained for most (22) of the species. Combined with the high Z (0.85–3.40) and M (0.73–3.10) estimates, these results imply low annual survival and high turnover rates. All 25 species exhibited year-round recruitment, with 20 species having two recruitment peaks annually and five species having a single annual recruitment peak. The φ ′ (2.05–3.32) and M parameters obtained were consistent with those available in the literature for the 25 species. The values of F (0.03–0.72) and E (0.02–0.27), however, were low compared to other assessments conducted in South and Southeast Asia. Estimates of E for the 25 species were also low compared to the E 0.1 (0.31–0.42) reference points obtained from the Y/R and B/R analyses. Low length-at-first capture was evident for 6 of the 25 species, although this is technologically difficult to avoid in multispecies fisheries. Overall, the results indicate that the 25 fish species were lightly fished in 1989–1990. The results provide baseline information (as well as reference points) that can be incorporated into wider reference systems relevant to current fisheries assessment and management in Brunei Darussalam, and are relevant to further (multispecies or ecosystem) studies of fisheries in the country and the region.