Open Ocean Giants

Few refuges from fishing on the high seas

Ocean-going sharks and rays face intense fishing pressure in international waters. A 2021 analysis (opens in a new tab) co-authored by MMF co-founder Dr. Andrea Marshall estimated that the global abundance of oceanic sharks and rays declined by 71% between 1970 and 2018. It attributed that decline to an 18-fold increase in relative fishing pressure, and found that three-quarters of the 31 oceanic species were threatened with extinction.

A 2019 global study in Nature (opens in a new tab), co-authored by MMF’s Simon Pierce and Chris Rohner, had already shown where that pressure falls. It compared the satellite tracks of ocean-going (pelagic) sharks, whale sharks among them, with the movements of global fishing fleets, and found that 24% of the mean monthly space used by the tracked sharks fell under the footprint of pelagic longline fisheries. That overlap reached 64% in the space-use hotspots of internationally protected species, the areas those sharks used most intensively. The authors concluded that pelagic sharks have limited refuge from current fishing effort on the high seas, and called for conservation and management measures at their high-seas hotspots.

Important areas on the high seas

The IUCN Species Survival Commission’s Shark Specialist Group identifies Important Shark and Ray Areas (ISRAs) using global scientific criteria. An ISRA is not a protected area and creates no new rules. Instead, it gives governments, fisheries managers, and marine planners independent evidence to guide decisions about how these waters are managed.

Several ISRAs extend into the high seas. The Pacific Equatorial Front (opens in a new tab) lies mostly beyond national jurisdiction in the Eastern Tropical Pacific and qualifies as a whale shark feeding and movement area. Evidence for its movement criterion includes research on whale shark migrations (opens in a new tab) co-authored by MMF’s Chris Rohner.

The Gulf of California–Revillagigedo–Clipperton Migration Corridor (opens in a new tab) spans Mexican and French waters and areas beyond national jurisdiction. Its evidence for whale shark movements includes the Pacific Mexico tracking study co-authored by Simon Pierce, and oceanic manta rays are also among its qualifying species.

The Eastern Tropical Pacific Marine Corridor (opens in a new tab) extends into international waters from Costa Rica, Panama, Colombia, Nicaragua, Honduras, Ecuador, and northern Peru. It is recognized as a feeding area for both whale sharks and oceanic manta rays. Diet studies co-authored by Andrea Marshall form part of the evidence for its importance to manta rays.

Protection under the Convention on Migratory Species

The Convention on Migratory Species (CMS) provides a framework for the countries that share migratory animals to cooperate on their conservation. Its Appendix I requires countries within a species’ range that have joined the convention to prohibit taking (capturing or killing) listed species, with limited exceptions. Whale sharks were listed on Appendix II of CMS in 1999 and, following their classification as Endangered, were added to Appendix I in 2017. Dr. Simon Pierce wrote the technical proposal for that uplisting, which the Philippines put forward as lead proponent. The oceanic manta ray was listed on CMS in 2011, after Andrea Marshall and the MMF team worked with the government of Ecuador to champion the listing. The reef manta ray followed in 2014.

For the CMS Secretariat, Simon co-authored the fact sheets Human Impacts on Sharks and Rays (2022), and Chris Rohner co-authored a 2023 report on limiting ship strikes on whale sharks. A 2026 study co-authored by Chris and Simon (opens in a new tab) established the first baseline of migratory connectivity, the links that animal movements create between places, for the CMS-listed sharks and rays of Australian waters. It documented five species linking Australia with other countries, but found no movement data for 18 of the 29 species reviewed. That gap limits the evidence available to coordinate their conservation across borders (read the story).

Oceanic manta rays and devil rays

Oceanic manta rays have been listed as Endangered on the IUCN Red List since 2020, yet their movements in the open ocean remain poorly known. Dr. Madalena Cabral of Cuidando los Mares de México leads research at Mexico’s Revillagigedo National Park, 400 km (250 miles) south of the Baja California peninsula. We contribute expeditions and photo-identification, which distinguishes individual rays by the spot patterns on their bellies. Satellite tags have been deployed there to follow the rays beyond the park’s boundary.

In Hawaii, oceanic mantas are often encountered far from shore. We are compiling sightings from researchers and the diving community to describe where they occur around the islands. Off Ecuador, a 2022 study (opens in a new tab) co-authored by Andrea Marshall identified 2,803 individual oceanic manta rays from photographs taken between 2005 and 2018. The study concluded that coastal Ecuador and Peru likely hold the largest population of the species in the world.

Several devil ray species are encountered so rarely that even their ranges are still being mapped. In the western Atlantic, Jessica Pate and our Florida team combine aerial surveys, fisheries records, and photographs from community scientists to document where these rays occur. A 2023 study (opens in a new tab) extended the known northern range of the sicklefin devil ray (Mobula tarapacana) in the western North Atlantic. A 2025 study (opens in a new tab) led by Jessica then mapped the distributions of the sicklefin, spinetail (M. mobular), and bentfin (M. thurstoni) devil rays across the western Atlantic and Caribbean. Next, we plan research expeditions with the Shared Seas Lab to study manta and devil rays off the northeastern United States.