UH study: No-fishing zones benefit ʻahi, other large fish species

A new study led by two University of Hawaiʻi at Mānoa researchers recently published in Science shows carefully placed no-fishing zones 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,” study co-author John Lynham, a professor in the Department of Economics at UH-Mānoa’s College of Social Sciences, said in a press release.

The recovery is good news for the environment and the global tuna fishing industry, which generates $40 billion in revenues each year and supports millions of jobs around the world.

It is well-known that no-fishing zones can benefit sedentary marine life, such as corals or lobster. However, until now it was assumed that no marine protected area could be big enough to protect species that travel long distances.

Using data collected onboard fishing boats by scientific observers, the study found that the world’s largest no-fishing zone, Papahānaumokuākea Marine National Monument, has increased the catch rate of yellowfin tuna by 54% in nearby waters. Catch rates for bigeye tuna, also known as ʻahi, increased by 12%; catch rates for all fish species combined increased by 8%.

Aside from their economic significance, yellowfin tuna and bigeye tuna have long held a central place in Hawaiʻi’s culture and diet.

“Being born and raised in Hawaiʻi, I know how important ʻahi is to the community here,” study co-author Sarah Medoff, a researcher at the UH-Mānoa’s School of Ocean and Earth Science and Technology, said in the press release. “It’s not just something eaten in fancy sushi restaurants, it’s the focal point of family gatherings, weddings, birthdays, graduation ceremonies and New Year’s Eve parties. It’s reassuring to know that the monument is protecting this resource for my own children and for future generations.”

Papahānaumokuākea was created in 2006 and expanded in 2016 to protect biological and cultural resources, not specifically to generate benefits to the local tuna fishery. The area is considered sacred by Native Hawaiians and the monument is co-managed by Native Hawaiians, the state of Hawaiʻi and the federal government.

The size of this no-fishing zone — almost four times the size of all the land in California — and the apparent homing behavior of some tuna species in the region, likely played a role in the positive effects observed.

“Over the past 30 years, we have learned that tunas do not venture as far away from home as we once thought,” study co-author Jennifer Raynor, a professor in the Department of Forest and Wildlife Ecology at the University of Wisconsin-Madison, said in the press release. “The Hawaiian Islands are a nursery for baby yellowfin tuna, and it turns out that many of these fish stay in the region.”

According to Kekuewa Kikiloi, an associate professor in the UH-Mānoa Kamakakūokalani Center for Hawaiian Studies, who was not involved in the study, the research reaffirms the value of large scale marine protected areas in the Pacific.

“The protections that were fought for by Native Hawaiians and other stakeholders for Papahānaumokuākea serve to benefit everyone, including fishing interests,” Kikiloi said in the press release.

The research was funded by the National Oceanic and Atmospheric Administration, and the National Science Foundation.