Changes in habitat preference of tuna species and implication for regional fisheries management: southern bluefin tuna fishing in the Indian Ocean

Changes in the ocean’s physical environment and its impact on ecosystems are well recorded in the literature and are likely to impact on the range and distribution of tuna species. This paper examines the impacts of these factors on the southern bluefin tuna (SBT) (Thunnus maccoyii), a species of low population abundance that is the focus of a high-value fishery. Oceanic warming has been projected to facilitate the expansion of such tropical tunas whilst reducing the northern distribution of temperate tunas such as the SBT. The study analysed the distribution of SBT using historical fisheries data collected by the Commission for the Conservation of SBT and the Indian Ocean Tuna Commission with the latitudes of fishing events and catches used as a proxy for SBT presence. Whilst these data do not provide conclusive evidence of a southerly shift in habitat preference, they do show increasing overlap between the SBT and with yellowfin tuna (Thunnus albacares). The paper concludes that while shifts in fishing effort in the Indian Ocean have a number of potential drivers, including changes in fish habitat, they highlight potential challenges to current regional management arrangements.