A national proposal that pits environmentalists against the fishing industry would have an outsized impact on Hawaii: a huge expansion of the Papahanaumokuakea Marine National Monument (PMNM).

Advocates want President Barack Obama to use the Antiquities Act to expand PMNM from its current 50-mile-out boundary to 200 miles out — encompassing the entire U.S. exclusive economic zone (EEZ) around the Northwestern Hawaiian Islands, making it the world’s largest marine reserve.

It’s an audacious idea, and not without negative consequences. Access to the area could be heavily restricted and regulated. Moreover, Hawaii’s commercial longline fishing fleet would be banned from laying its hooks over the roughly 600,000 square miles the PMNM would encompass. That could have an impact on the supply of fresh fish on our docks.

On balance, however, expanding the monument is the more sensible option. Given the relentless pressure on the oceans’ ecosystems from both man and nature — an aggressive fishing industry, a warmer Western Pacific, pollution, alarming declines in certain marine species — public policy should follow the best available science to ensure the health of Hawaii’s ocean environment and wildlife for generations to come.

Robert Richmond, a research professor and director of the Kewalo Marine Laboratory, told the Star-Advertiser editorial board that truly effective marine conservation requires protecting areas of relative isolation that encompass many diverse habitats and unique species — features which Papahanaumokuakea possesses in abundance, at least for now.

The area contains an interdependent web of wildlife, from the fish we eat to 4,000-year-old corals.

Moreover, a five-fold expansion of the reserve reflects the proportions needed for the buffer required to protect this marine life from the broad impacts of global climate change, said Richmond, who is one of a large number of scientists who signed a letter to Obama urging him to expand the reserve for these reasons.

But does that mean Hawaii’s small commercial fleet of 140 longline fishing boats should be banned?

That’s a trickier question.

The Western Pacific Regional Fishery Management Council, an unapologetic booster of the fishing industry, says its scientists believe Hawaii’s fishing fleet has a negligible impact on the EEZ, and that banning fishing in the EEZ will only harm Hawaii’s economy and the fishery without benefitting conservation.

In an April letter to Obama, council officials argued that “if these Hawaii vessels are forced to fish on the high seas, they faced increased competition with foreign vessels, lower catch rates, and higher operating costs.”

The numbers tell a more nuanced story. The fleet already operates on the high seas, by choice, because that’s where the fish are. Recent data on Hawaii’s longline vessels gathered by the Pacific Islands Fisheries Science Center show that most of the fishery’s harvest already comes from outside the EEZ — upwards of 90 percent or more, depending on the year.

Moreover, in 2014, the fleet caught a record 216,897 prized bigeye tuna, Hawaii’s source of locally caught fresh ahi. And while the loss of the EEZ would impose a burden to the fishery, it’s not likely to be a fatal one. A closed EEZ would not prevent the fishery from catching its full quota, which could be collected elsewhere, as it mostly has been.

It also should be noted that in 2014, the fishery hooked 5,662 sharks within the EEZ, but kept only 44. Overall that year, the fishery caught 85,067 sharks and kept less than 1 percent of them. Sharks, while hugely important in a balanced marine ecosystem, are mere bycatch for the fishery.

Such bycatch is part of longline fishing, which employs what Richmond called “a wall of hooks” — 47 million hooks deployed by the Hawaii fishery in 2014, a strong argument that the effects of longline fishing are not benign.

Among the advocates who have urged Obama to expand PMNM are U.S. Sen. Brian Schatz, who has proposed allowing small-time fishers access to the eastern edge of the EEZ; and a group of prominent Native Hawaiians, including William Aila, Nainoa Thompson and Kamana‘opono Crabbe, CEO of the Office of Hawaiian Affairs (OHA).

Indeed, OHA wants to be a co-trustee of an expanded PMNM, so it can represent Native Hawaiian interests on equal footing with the state of Hawaii and the federal agencies that would manage the monument.

While the cultural importance of all the Hawaiian islands to the Native Hawai- ian community cannot be denied, such an arrangement raises jurisdictional questions about the role of OHA, which is a state agency.

Proponents of an expanded PMNM hope to entice Obama to approve the expansion and announce it, in person, at the International Union for Conservation of Nature Congress, to be held in Hawaii in September. That would be a public relations coup — though closing off such a large section of Hawaiian waters, even for the best of reasons, will come at a cost. The amount remains to be seen.