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Abstract

The silky shark, Carcharhinus falciformis, is a common bycatch species of tuna and swordfish longline fishing in the Indian Ocean. The high value of its fins makes it one of the most heavily fished shark species in the world. Concern over declining populations and the uncertainty surrounding its population dynamics has increased the urgency of developing appropriate methods to assess its stock status. This study developed a two-sex stage-based structured matrix model with Monte Carlo simulations to examine silky shark demography and population dynamics. The simulations indicate that, without mortality from fishing, the stock will increase slightly (sex combined mean annual population growth rates were 1.079 yr-1 and 1.030 yr-1 for 1-yr and 2-yr reproductive cycles, respectively). However, our analysis of various management scenarios shows that even with low levels of fishing mortality, the silky shark population may be on the edge of collapse. This study indicates that the protection of immature sharks is the most efficient conservation measure for this species, and that this will produce higher population growth rates than the protection of mature sharks only. As the data on stock status are inadequate, better estimates of current fishing levels are needed to obtain a more accurate estimate of the impact of fishing on the population. Against a background of increasing global shark catches and landings, it is important that silky shark populations are constantly monitored to ensure their sustainability in the Indian Ocean. We believe that the framework developed in this study can be used to evaluate the risk of decline among other widely distributed

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