Six years ago, the then U.S. president, Barack Obama, created the world’s largest fully protected ocean reserve by expanding the existing Papahānaumokuākea marine national monument in Hawaii, a world heritage site that include islands, atolls and archeological treasures.
Now scientists have found that the reserve, which spans 1.5m sq km (580,000 sq miles) and is inhabited by whales and turtles, has brought unexpected benefits to the surrounding ocean.
Catches of yellowfin tuna, known as ahi in Hawaiian, were found to have risen by 54 percent between 2016 and 2019 near the reserve, within which fishing is banned, while catches of bigeye tuna rose by 12 percent.
The findings, published in the journal Science, by researchers from the University of Hawaii and the University of Wisconsin-Madison may strengthen support for a target, agreed by more than 100 countries, to protect 30 percent of the world’s oceans by 2030.
“This research is important because it helps us understand that a large, carefully placed no-fishing zone can create benefits for these large iconic species,” said Jennifer Raynor, an environmental economist at the University of Wisconsin-Madison and one of the paper’s three co-authors.
Although marine protected areas (MPAs) have repeatedly been shown to protect local populations of fish, previous research has cast doubt on their potential to provide so-called spillover benefits for migratory species, such as tuna and swordfish, as many MPAs are small compared with the geographic range of these species.
“The protected area could be doing one of two things,” said Raynor. “The first is that these iconic fish populations are increasing because the areas provide nurseries for baby fish, and some of them are spilling over into nearby areas. A second reason might be that fish are just finding a safe place to aggregate, near the protected area, where they can’t be caught.”
She said the research could help demonstrate that MPAs are a worthwhile investment.
“By setting up no-fish zones, we are forcing people to stop fishing in places that they previously enjoyed,” she said. “But it is like an investment. You make big upfront costs, with the hope that it will pay off in the future, like having higher tax rates over time. Our paper says: if you create these areas carefully, then that investment can pay off.”
The scientists used data from the U.S National Marine Fisheries Service’s Pacific Islands observer programme, which monitors the Hawaii-based longline fishery catching bigeye and yellowfin tuna. The largest increases in catches were seen at distances of between about 100 and 200 nautical miles (185-370km) from the reserve’s border. As a control, they compared fish catches from 2016-19 with catches between 2010 and 2013, before the reserve’s expansion. They found no significant increase or “spillover benefit” before 2016.
MPAs are often declared by governments without any accompanying prohibition on commercial fishing, leading to criticisms that the reserves are simply “paper parks” with no real protection from damaging extractive activities. In Papahānaumokuākea, however, commercial fishing is banned. While the area’s remote location makes enforcement difficult, the park has officers patrolling in addition to monitoring flights and visits by US coastguard vessels to deter illegal fishing.