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Fifty years ago today, Congress passed the Marine Mammal Protection Act (MMPA), a law that set the global benchmark for conserving marine mammals. It was the first piece of legislation to call specifically for, “an ecosystem-level approach to wildlife protection.” According to the National Oceanic and Atmospheric Administration (NOAA), not a single marine mammal species has gone extinct in US waters since the law was passed in 1972, and the protections enacted have helped stop declines among many marine mammal species. The policy has even led to the recovery of many species including gray seals, California sea lions, and humpback whales.

In the Pacific Ocean, fish and humans alike are seeing some of the same benefits from strong regulations. At 582,578 square miles, the Papahānaumokuākea Marine National Monument in Hawaii is the world’s largest no-fishing zone and marine protected area (MPA). It was established in 2006 and expanded 10 years later with the goal of, “seamless integrated management to ensure ecological integrity and achieve strong, long-term protection and perpetuation of NWHI ecosystems, Native Hawaiian culture, and heritage resources for current and future generations.” And it appears to be working.

[Related: Eating sustainably may mean skipping the lobster for now.]

A study published this week in the journal Science finds that carefully placed no-fishing zones like Papahānaumokuākea can help restore tuna and other large fish species. “We show for the first time that a no-fishing zone can lead to the recovery and spillover of a migratory species like bigeye tuna,” says co-author John Lynham, a professor in the Department of Economics at the University of Hawaiʻi at Mānoa’s College of Social Sciences, in a press release.

The team used data collected from fishing boats and found that the catch rate of yellowfin tuna increased by 54 percent in the fishable waters close to the Papahānaumokuākea protected area since 2010. Additionally, the catch rates for bigeye tuna increased by 12 percent and it was 8 percent for all fish species combined in the years since the MPA was expanded.

Fish populations thrive near marine protected areas—and so do fishers
The spillover benefits to fish catches from Hawaii’s Papahānaumokuākea Marine National Monument. CREDIT: Sarah Medoff, John Lynham, and Jennifer Raynor.

Both the size of the no-fishing zone (about four times the size of California) and apparent homing behaviors of some tuna species possibly played a role in these positive effects. The Hawaiian islands appear to be a nursery for baby yellowfin tuna and many of the fish stay in the region, according to study co-author Jennifer Raynor, a professor in the Department of Forest and Wildlife Ecology at the University of Wisconsin-Madison.

[Related: A tuna robot reveals the art of gliding gracefully through water.]

Additionally, the positive results seen in this study aren’t necessarily an isolated global incident. “This study echoes similar work done in the Galapagos Marine Reserve, showing large and persistent fishery benefits for highly migratory species,” Boris Worm from the Department of Biology at Dalhousie University in Nova Scotia says in an email to Popular Science. “It builds a strong case for large-scale marine protected areas not just as biodiversity conservation, but as fishery rebuilding tools. Responsible fishing and conservation do not oppose each other – they are two sides of the same sustainability strategy.” Worm was not involved in the study.

These big fish are also big business. Fortune Business Insights estimates that the global tuna fish market will be worth $48.19 billion by 2028. Yellowfin tuna and bigeye tuna (which you may have seen listed on a sushi menu as ʻahi) cost an average of $28 to $35 per pound and the most expensive on record sold for more than $3 million at a 2019 auction in Tokyo, Japan.

However, they are are historically important to Hawaii’s diet and culture. One of the study’s co-authors, Sarah Medoff, was born and raised in Hawaii and pointed to how ‘ahi is a focal point at family gatherings and celebrations, and conservation will ensure that that tradition can continue.

“Conservation and economic progress are often viewed as opposing forces, meaning, you cannot achieve one without sacrificing the other. This study is a perfect example of how conservation objectives can be met without sacrificing the livelihood of people who depend on this resource. If we construct a well thought out conservation plan, we can reverse environmental damages,” Medoff, a researcher at the School of Ocean and Earth Science and Technology at the University of Hawaiʻi at Mānoa, says in an email to Popular Science.

Papahānaumokuākea is considered sacred by Native Hawaiians and the monument is co-managed by Native Hawaiians and the state and federal government. “This research by Medoff et al. reaffirms the value of large scale marine protected areas in the Pacific,” Kekuewa Kikiloi, associate professor in the Kamakakūokalani Center for Hawaiian Studies at the University of Hawaii at Mānoa, says in a press release. “The protections that were fought for by Native Hawaiians and other stakeholders for Papahānaumokuākea serve to benefit everyone, including fishing interests.”