Seasonal distribution patterns and conservation gaps of blue sharks in the Indo-Western Pacific Ocean

Aim

Oceanic sharks play an important role in maintaining the stability and biodiversity of marine ecosystems, and yet they are among the most threatened taxa worldwide. Currently, large spatial-scale distribution patterns and conservation gaps are poorly known for most species since they are challenging to study. To address the problem, we here use an integrated approach with an illustration with the blue shark (Prionace glauca), a common bycatch oceanic species.

Location

Indo-Western Pacific Ocean (IWPO).

Methods

We first collated decades of species occurrences and marine environmental datasets from open-access sources. We then applied ensembled species distribution models (SDMs) to predict its seasonal distributions and evaluated the model performance using true skill statistic (TSS) and area under the receiver-operating characteristic curve (AUC). We finally conducted spatial analyses (e.g. bivariate hotspot analyses) to identify conservation gaps/opportunities based on the predicted distribution maps and two additional datasets, namely, marine protected areas (MPAs) and fishing effort.

Results

(1) Both seasonal SDMs performed well (mean TSS > 0.8, AUC > 0.95), and the results suggested that blue sharks were widely distributed in the IWPO with some seasonal differences in ecological niches and distributions (mainly in the West Indian Ocean and the Northwest Pacific Ocean); (2) large MPAs and shark sanctuaries covered comparable, small portions (4%–9%) of blue shark habitats, but these locations (in MPAs and sanctuaries) varied between seasons; (3) fishery-shark conflict hotspots also varied between seasons with some located in or close to large MPAs and sanctuaries.

Main conclusions

We provide seasonal (cold vs. warm) distribution maps of blue sharks across the IWPO to advance their conservation and management. We highlight the importance of strengthening management both in and near large MPAs and shark sanctuaries. Our study contributes a feasible integrated approach to reveal seasonal distribution patterns and conservation opportunities for oceanic sharks.