A new study by Hawaii scientists offers more evidence that ocean sanctuaries are not only good for the marine life inside the protected zones, but they create spillover effects that act to expand their borders.

In this case, the study published Thursday in the journal Science found that the number of bigeye and yellowfin tuna caught by fishing boats outside and near the Papahanaumokuakea Marine National Monument increased significantly from the time it was expanded in 2016.

Until now many questioned whether a marine protected area could be big enough to protect a species that travels long distances, such as a bigeye tuna, which has a range from 200 to 400 miles.

“There are lots of examples of smaller protected areas having spillover effects on sedentary life, such as lobsters,” said co-author John Lynham, a University of Hawaii at Manoa economics professor. “Now, for the first time, we show that a no-fishing zone can lead to the recovery and spillover of a highly migratory species like bigeye tuna.”

The study offers what appears to be good news to the tuna fishing industry, which has resisted the creation of expansive marine protected areas due to the loss of fishing grounds. The research suggests that a fisherman can compensate for some of the expense tied to fishing grounds losses by getting more valuable fish out of the water.

The study comes at a time when a number of governments, including the United States, have committed to protecting 30% of their oceans. Although several marine protected areas are being proposed around the world, there have been some setbacks, including the reopening to fishing of the Phoenix Islands Protected Area, a reserve the size of California, near Kiribati.

Using data collected aboard fishing boats by scientific observers from 2010 to 2019, the study found that the world’s largest no-fishing zone, Papahanaumokuakea Marine National Monument, increased the catch rate of yellowfin tuna by 54% in nearby waters.

Catch rates for bigeye tuna, also known as ahi, increased by 12%, while the catch rates for all fish species combined increased by 8%.

Lynham, an economist who has a master’s degree in marine biology, said the study grew out of a doctoral thesis started three years ago by co-author Sarah Medoff, a researcher at the UH Manoa’s School of Ocean and Earth Science and Technology. The third co-author is Jennifer Raynor, a professor of forest and wildlife ecology at the University of Wisconsin at Madison.

Anticipating pushback from the fishing industry, the scientists went out of their way to double- and triple-confirm their data with some 100 different tests using three different data sets and publicly available data, Lynham said.

Research professor Robert Richmond, director of UH’s Kewalo Marine Laboratory, who wasn’t involved with the research, called it “a valuable study and important contribution to broader knowledge on the value of large-scale marine protected areas in general and the Papahanaumo­kuakea Marine National Monument in particular.”

“This is a solid piece of research and clearly communicated,” he said.

Papahanaumokuakea was created in 2006 by President George W. Bush and expanded in 2016 by President Barack Obama to protect biological and cultural resources. At roughly 583,000 square miles, the monument — surrounding the Northwestern Hawaiian Islands — is the single largest fully protected conservation area in the U.S. and one of the largest marine protected areas in the world.

Not everyone’s a fan of vast marine protected areas. Two years ago the Western Pacific Regional Fishery Management Council wrote to President Donald Trump urging him to lift the fishing restrictions in the Pacific marine national monuments, saying Hawaii longline vessels face an unfair playing field as they compete with fishermen from other countries.

In September the council came out against the proposed expansion of the Pacific Remote Islands Marine National Monument, which would create the largest highly protected marine sanctuary in the world. A coalition of Hawaii scientists, conservationists and cultural practitioners is urging President Joe Biden to expand the monument.

Council fisheries scientist Mark Fitchett in 2021 co- authored a peer-reviewed paper that looked at a future where 30% of the world’s oceans are covered by fixed ocean sanctuaries, and suggested there may be a better way to protect fishing stocks.

Analyzing 15 fisheries around the globe, the paper found that under static area management, observed bycatch could be reduced by 16%. However, under a more dynamic ocean management, based on observed bycatch and closing the same total area but fragmented in smaller areas that can move year to year, reduction increased up to 57% at minimal or no loss of target catch, the research found.