Falling short of expectations: Scientist says marine protected areas don't guarantee tuna repopulation

By Mar-Vic Cagurangan

Aquatic resources within marine protected areas do not repopulate as much as commonly believed, a fishery scientist said, citing recent studies suggesting that large sanctuaries do not live up to expectations.

Ray Hilborn, a professor with the University of Washington, said recent studies have found no measurable increase in tuna biomass density inside open-ocean protected areas.

He noted that substantial ecological responses to marine closures are particularly unlikely in U.S. monument waters, where fishing pressure is relatively low.

“This refers to the pelagic fisheries," Hilborn said in an email to the Pacific Island Times. "The catch of tunas in most of the U.S. territory EEZ was relatively low, so you just don't expect to see much of a change."

He delivered a presentation at the Scientific and Statistical Committee’s 158th meeting in Honolulu, where the scientific panel weighed the pros and cons of restoring commercial fishing in U.S. Pacific marine national monuments in response to President Trump’s April directive.

The target areas are the Marianas Trench, Papahānaumokuākea and Rose Atoll national monuments.

Hilbron declined to take a stand on the Trump administration's policy to open marine monuments to commercial fishing.

"That is totally a political decision," he said in an email to Pacific Island Times. "My role is to give science advice on the consequences."

According to a press release from the committee, Hilbron examined the limited data available from within existing monument closures, new information from recent reopenings, and economic performance of U.S. longline vessels before and after closures.

He cited a study on the Phoenix Island Protected Area, published by Dr. John Hampton of the Pacific Community, which found that the no-take zone “does not have discernible conservation benefits for Pacific skipjack and bigeye tuna, two of the most important tropical tuna species to U.S. fisheries.”

In some cases, the study said, substantial reductions in bigeye catch-per-unit-of-effort linked to the loss of historically productive grounds.

The 408,250-sqkm Phoenix sanctuary is a UNESCO World Heritage site located about halfway between Hawai‘i and Fiji. It was once the world’s largest marine protected area.

Hilborn, a member of the committee under the Western Pacific Regional Fishery Management Council, presented an analysis that compared widely promoted claims that large marine protected areas increase biodiversity, create healthier ecosystems and support sustainable fisheries with empirical evidence from the Pacific.

Marine monuments are established to protect aquatic ecosystems, preserve biodiversity and provide habitats for natural resources to thrive.

Hilborn, however, argued that closures of marine national monuments create an illusion of “protection” while leaving non-fishing threats ignored.

"For the Pacific island areas, the major non-fishing threat is probably climate change, but also includes invasive species, pollution and plastics," he said.    

Hilborn told the committee that well-regulated U.S. fisheries under the Magnuson–Stevens Act are unlikely to pose an abatable threat to pelagic stocks and that any threat can be addressed by creating large marine protected areas alone.

He said the Magnuson–Stevens Act's management frameworks and the Western and Central Pacific Fisheries Commission already provide tools to achieve conservation goals while considering human and community impacts.

Eric Kingma, executive director of the Hawaii Longline Association, said existing monument area closures “exclude U.S. vessels from U.S. waters and leave us very constrained in where we can fish.”

Citing declining bigeye catch rates, Kingma emphasized that “we need to be able to find and follow the fish – that’s the most important part.”

“We’re not looking for more fish, but to have the opportunity to fish more efficiently away from competitors,” Kingma said. 

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