- New rules that apply to a vast swath of the Pacific Ocean aim to improve manta and devil rays’ chances of surviving encounters with tuna fishing boats.
- The measure prohibits fishers from targeting the rays or keeping the ones they catch accidentally. It also mandates that fishers release rays that survive being caught in a manner “that will result in the least possible harm.”
- Growth in demand for manta and devil ray gill plates and anecdotal reports of decreasing populations have raised concerns about the effects of overfishing, both intentional and accidental.
Purse seine fishing nets may be set for tuna, but they trap whatever fish swim into them, including manta and devil rays. As the net tightens, rays will panic and thrash. Trauma and death by suffocation in the crush of fish are likely outcomes. But even those rays lucky enough to survive the net face further challenges. Tuna fishers don’t really want a 1,600-kilogram (3,500-pound) oceanic manta (Mobula birostris) flopping around on deck, but large mantas aren’t easy to put back into the ocean. Crews might hoist a ray overboard by hooking it through its gill plates or running a cable through a hole punched in its fin. This may explain why a 2016 New Zealand study found that less than half of rays released alive survive.
New rules that apply to a vast swath of the Pacific Ocean aim to improve manta and devil rays’ chances of surviving encounters with fishing boats. In December 2019, the Western and Central Pacific Fisheries Commission (WCPFC) adopted a measure prohibiting fishers from targeting the rays or keeping the ones they catch accidentally, and mandating that they release living rays in a manner “that will result in the least possible harm.” The multilateral body manages fisheries in the region and includes some of the world’s largest tuna-fishing nations among its members: Japan, Indonesia, and the Philippines.
Manta and devil rays, newly grouped into eight species in the genus Mobula, are generally large-bodied planktivores that live in tropical and temperate waters around the world. Females usually give birth to a single pup every one to five years, making mobulids vulnerable to overfishing. Growth in demand for their gill plates and anecdotal reports of decreasing ray populations have scientists worried.
The WCPFC mobulid protection measure comes five years after its initial introduction as a set of non-binding guidelines, according to biologist Wetjens Dimmlich, director of fisheries management for the Pacific Islands Forum Fisheries Agency (FFA). The FFA helped push the measure’s adoption, with support from all of the FFA’s 17 member nations — half the entire WCPFC membership. Passing the measure was an accomplishment because it represented the commitment of major fishing nations such as Japan and the Philippines to upholding its provisions at their ports and on ships flagged to them.
Several factors contributed to the measure’s adoption, Dimmlich said. It helped that the Indian Ocean’s fisheries management body had just implemented a similar measure; that the region encompasses some of the most lucrative (and growing) manta tourism in the world; and that WCPFC’s small member country of Palau, a dive-tourism destination, had just preserved 80% of its national waters as a marine sanctuary.
Tuna boats will bear the brunt of the measure’s stipulations. Guidelines for getting trapped rays safely back into the sea include tending immediately to live animals, careful handling (gripping fins not gills), untangling the animals from gear, and using special equipment rather than the ubiquitous hooks and gaffs. The measure also encourages fishers to work with satellite-tagging programs that track the rays for research purposes.
The eastern Pacific’s fisheries management body, the Inter-American Tropical Tuna Commission (IATTC), enacted similar protections for mobulids in 2015. All IATTC member tuna boats of more than 363 tons (which is most commercial boats) have onboard observers, so the fishery is poised to collect useful scientific and compliance data.
The IATTC has been honing its conservation protocols since the 1960s, mainly to protect dolphins. Boats are set up with conveyors at the sorting point that conduct unwanted animals directly back to sea. But for many boats under the WCPFC, where the work of conveyors is still done by humans and efficiency has been a higher priority than rescuing bycatch, implementation remains a work in progress.
“Most fishery measures take considerable time to implement,” said Daniel Fernando, a director of Blue Resources Trust, a Sri Lankan NGO that supported the mobulid regulations in the Indian Ocean.
