Preliminary Ecological Risk Assessment (ERA) for shark species caught in fisheries managed by the Indian Ocean Tuna Commission (IOTC)

Ecological risk assessment (ERA), and specifically Productivity-Susceptibility Analysis (PSA), is a useful methodology for assisting the management of fisheries from an ecosystem perspective in a data poor situation. Indian Ocean tuna and tuna-like fisheries, managed by the Indian Ocean Tuna Commission (IOTC), are economically important both at local and international scales and interact with several non-target or bycatch species. In spite of these interactions, to the authors best knowledge, no comprehensive ERA has been conducted for bycatch species in general, neither for sharks, caught by IOTC fisheries. A PSA for shark caught in various longline and purse seine fleets operating in the Indian Ocean was carried out. We follow the methodology proposed by Cortes et al. (2010), which allow ranking the vulnerability of the species based on its productivity and susceptibility to the fishing gear. We estimate the species productivity parameters based on Leslie matrices analysis, in which the value of Lambda (λ), population finite growth rate, was calculated (Caswell 2001). The species with the least productivity values are two coastal shark species (Carcharhinus plumbeus and Carcharhinus obscurus), followed by several Lamniformes (Isurus paucus, Alopias superciliosus, Lamna nasus and Isurus oxyrinchus). As had been previously observed for other Oceans, such as the Atlantic (ICCAT, 2012), the blue shark (BSH) seems to be the pelagic shark species with the higher values of biological productivity. The susceptibility analysis for the effects of fishing on sharks was carried for the European purse seiner, Soviet Union purse seiner, Soviet Union research longline, Japanese longline, Korean longline, La Reunion Island longline, Chinese longline fleets; for which observer or research data were available, and also for all longline fleets and purse seine fleets combined. The effort distribution, for each fleet as well as for all the fleet combined (LL vs. PS); the vertical overlap between the species and fishing gear; the selectivity; and post-capture mortality was assessed to estimate the susceptibility of each shark species to particular fishing gear.