Can we Derive an Abundance Index for the Silky Shark Based on its Associative Behavior with Floating Objects?

Using data from the French tropical tuna purse seine fishery, this study proposes a new method to derive an abundance index for silky shark’s populations. Two models were used: the first one describes the dynamics of sharks associated to floating objects (FOBs) used by tuna purse seiners in a social and in a non-social case. The second one illustrates the exchanges of individuals between the FOB-associated population and an external pool of sharks. The parameters estimates of the first model were obtained with fitting analysis. These parameters were then integrated into the second model. By approximating an unknown parameter (𝛾!), abundance indices were derived. This approach also allowed the construction of short-term temporal series relative to a reference year. This methodology has the potential to be applied to any other species associating with FOBs and serve as a tool for fisheries management.