Just northwest of the Hawaiian Islands lies the Papahānaumokuākea Marine National Monument — a vast 583,000-square-kilometer swath of federally protected coral islands, seamounts, shoals, and deep-sea expanses that host a wide diversity of marine flora and fauna, much of which are unique to the region and some dangerously endangered. The monument covers more area than all of America's national parks combined and is the world's largest no-fishing zone.
Since its dedication in 2006 and its most recent expansion in 2016, Papahānaumokuākea's goal has been to protect and preserve the marine life that calls the monument home.
Now, researchers have found that the benefits of Papahānaumokuākea's stringent protection extend beyond its borders and have helped revive stocks of large migratory fish, specifically the commercially important yellowfin and bigeye tuna that often frequent the area surrounding the monument.
According to a new study, this spillover effect has led to significantly increased commercial catch rates for these fish in nearby waters outside of the Papahānaumokuākea marine protected area (MPA). The findings, published in the October 21 issue of Science, show that commercial catch rates for yellowfin tuna increased by 54% since Papahānaumokuākea's 2016 expansion. Catch rates for bigeye tuna also have increased by 12%.
"This study is a perfect example of how conservation objectives can be met while still supporting the livelihoods of fisherman that depend on this resource," said Sarah Medoff, a researcher at the University of Hawai'i Mānoa and lead author.
Searching for Spillover Benefits
Unlike many smaller reef species, which tend to spend their lives close to their home habitats, large migratory ocean fish species like tuna and swordfish can have ranges that can span ocean basins and, more importantly, the boundaries of designated MPAs and international fishing zones.
"It is relatively uncontroversial that marine protected areas can help restore species that don't move around much, like corals or lobsters," said Jennifer Raynor, a researcher at the University of Wisconsin-Madison and coauthor of the study. "But there is a debate about whether any protected area could be large enough to protect large, mobile species, like tunas."
Previous research has cast doubt on the ability of MPAs to provide refuge and benefits for large migratory species, as many MPAs are small compared to the species' natural geographic ranges. Moreover, identifying any potential spillover benefits associated with MPAs is challenging. As a result, the potential investment returns from marine conservation efforts are poorly understood.
Since Papahānaumokuākea is the world's largest contiguous no-fishing zone, it provides an ideal case study to investigate these questions, said Medoff.
To identify potential spillover benefits, Medoff and her colleagues evaluated species-specific catch-rate data for individual fishing vessels operating near to (up to 300 nautical miles) and far from (as much as 600 nautical miles) Papahānaumokuākea's boundaries both before and after its 2016 expansion.
The analysis revealed clear evidence that the protections afforded benefits for yellowfin and bigeye tuna outside Papahānaumokuākea's borders that were previously only seen for resident fish populations.
Yellowfin and bigeye tuna — a pair of species commonly known as ahi tuna and prized for their use in sashimi and sushi — are the most commercially important species in the region and account for almost half of all catch in the region.
"Globally, tuna fishing generates $40 billion in revenues each year and supports millions of jobs," said Raynor. "We show for the first time that marine protected areas can help to restore tunas and generate economic benefits for nearby commercial fishing."
Investing in Future Oceans
Many nations, including the United States, have committed to protecting 30% of their ocean territory by 2030. While the extent and details for these protections can vary significantly, achieving this goal will undoubtedly have an impact on commercial fishing worldwide.
While the fishing industry can be doggedly opposed to creating or expanding MPAs, Medoff and her colleagues show that large and carefully placed no-fishing zones can have an important spillover benefit and help to maintain surrounding fisheries for years to come.
"Marine protected areas are an investment in the future," said Raynor. "They impose a large upfront cost of lost fishing opportunities in the hope of later benefits from increased catch."
The spillover effects like those identified by Medoff, Raynor and the researchers offer a nice proxy for the overall health of the ecosystem that the MPA is protecting, signaling that the environmental investments are paying off.