Abstract

The Western Indian Ocean (WIO) is known for its high diversity of chondrichthyans (sharks, rays, and chimaeras). However, intense fishing pressure has led to severe population declines and local extinctions of several species. The Important Shark and Ray Area (ISRA) process is a collaborative, evidence-based approach used to identify critical habitat for chondrichthyans. We analysed ISRAs across the WIO to quantify the diversity of research methods used to identify them, evaluate spatial overlap with designated marine protected areas (MPAs), model the influence of several species- and jurisdiction-specific variables on ISRA delineation, and explore the importance of incorporating unpublished data into the delineation process. In total, 125 ISRAs (covering > 2.8 million km2; ~10% of total regional surface area) were identified within the WIO from surface waters to ~2000 m depth. These ISRAs contain over one-third (n = 104, 39%) of the 270 chondrichthyan species reported from the region, with 76% being threatened with extinction according to the IUCN Red List of Threatened Species. The underlying evidence supporting ISRA identification was primarily drawn from relatively inexpensive research methods, such as visual census (25%) or fish-market/landing site surveys (22.6%), as well as citizen science (9.5%). Incorporating unpublished records substantially increased the frequency of ISRA delineation, leading to expanded taxonomic and geographic coverage. Still, the full dataset was influenced by the same biases as the published record, tending to favour large-bodied, wide-ranging, and shallow-dwelling species. Only 7.1% of ISRAs are within designated MPAs, with just 1.2% in fully protected no-take areas. The highest no-take overlap occurs in the Seychelles and Chagos Archipelago. These findings highlight the shortfalls in spatial protection of chondrichthyan habitats, but also present a strategic opportunity for policy-makers and resource managers to improve current MPA coverage and meet their commitments under international agreements, such as the Global Biodiversity Framework.

Publication Date

2026-01-11

Publication Title

Ecology and Evolution

Volume

16

Issue

1

ISSN

2045-7758

Acceptance Date

2025-12-02

Deposit Date

2026-01-13

Funding

The Important Shark and Ray Areas project was funded by the SharkConservation Fund, a philanthropic collaborative pooling expertiseand resources to meet the threats facing the world's sharks and rays.The Shark Conservation Fund is a project of Rockefeller PhilanthropyAdvisors. Special thanks are extended to the Important Shark andRay Areas (ISRA) Independent Review Panel composed of ColinSimpfendorfer, Ana Barbosa Martins, Vanessa Jaiteh, and Eva Meyers,who reviewed and provided feedback on all ISRA proposals. Finally, wethank our web developer Elena Politi for support with the ISRA eAtlasand all those who contributed their knowledge and expertise to help de-lineate ISRAs and Areas of Interest in the Western Indian Ocean region

Keywords

biodiversity, conservation, fisheries, global biodiversity framework, marine spatial planning, threatened species

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