Op-ed: Research papers misrepresent impacts of marine protected areas

Ray Hilborn is a professor at the University of Washington’s School of Aquatic and Fishery Sciences and a fellow of the Royal Society of Canada, the American Academy of Arts and Sciences, and the Washington State Academy of Sciences. He has been awarded the Volvo Environmental Prize and the International Fisheries Science Prize and has published over 300 papers in peer-reviewed scientific journals.

A paper from Ocean University of China Researcher Mark John Costello,Evidence of economic benefits from marine protected areas,” published on 27 March in Scientia Marina, which concluded marine protected areas (MPAs) boost overall economic performance of fisheries, contains many factual errors and violates the standards of a review of the subject.

The most serious error the paper makes is claiming evidence of economic benefits from studies that did not show benefits. As an example, Costello cites Lynham 2020, saying this paper showed “that catch and CPUE were higher for longline fisheries,” whereas the actual paper stated that the MPA “had little, if any, negative impact on the fishing industry.” A more detailed study conducted later by Chan showed a negative impact on the individual vessels who had previously fished in the MPA by having to travel farther.

In almost every case cited by the paper, economic benefits were shown by higher catches or size near MPAs, known as “spillover.” Yet, spillover is always expected on the edge of an MPA, and the paper does not provide evidence that those higher catches made up for lost catch from the area when it was closed. However, in one of those cases cited, in which I was a co-author, we did find that the weight of catch outside the MPA was slightly higher than what was lost by the closure.

As another example, the paper claims “catch rates of trammel netters were 33 to 50 percent higher inside the trawl exclusion area than outside.” It is not a surprise that if you close an area to one fishing gear like trawling, the remaining fishing gears benefit. This does not mean marine protected areas provide a net benefit for catch totals.

Certainly, some MPAs have proved great tourist attractions and generated economic benefits, but most have not. In a recent review of the many MPAs set up on the California coast, it was found that tourism increased primarily in places where some harvesting was allowed.

It appears that Costello simply searched the literature for examples he could find that appeared, in his opinion, to show economic benefits. He cites 48 cases among the hundreds of studies of MPAs. His 48 examples do not represent a survey of the economic costs and benefits of MPAs. MPAs can have economic benefits, primarily when overfishing is intense, but there is no evidence that, on average, the benefits are real, or at the very least outweigh the costs.

There are also issues with “Divergent responses of pelagic and benthic fish body-size structure to remoteness and protection from humans,” published by Science in February 2024.

Using hundreds of thousands of camera photos, the paper by Letessier and co-authors found that inside MPAs, or at remote locations far from fishing pressure, the average size of fish was larger. They then argue that this means that MPAs are needed to recover size structure of fish populations and endangered species.

There is simply nothing new in their basic result. It has been known for 100 years that the average size of fish is reduced by fishing. Fishing causes fewer fish to grow older and larger. The size of fish should be smaller in a well-managed fishery compared to an unfished area.

For Letessier to show that in MPAs, or far from people, the average size of fish is smaller says absolutely nothing about whether the populations are overfished and in need of rebuilding. All they have done is confirm what other scientists have already know: If you close an area to fishing, or look far away from people, fish will be bigger. It hardly seems worthy of a paper in Science, or any press coverage.

The size distribution of fish does tell a lot about the amount of fishing pressure, though, and the absence of large fish is a common indicator of overfishing, but Letessier’s paper doesn’t show this. In fact, it makes no attempt to determine if the reduction in size structure is strong enough to indicate overfishing. Perhaps some of the places they had cameras were overfished, but looking at their map, most of their sites seemed to be in Australia, Norway, or remote islands, where overfishing is uncommon.

Having first shown something that is widely known to then arguing this difference in size indicates the need for MPAs is an amazing leap.

In the paper’s abstract, the authors write “recovery of the world’s largest and most endangered fishes in pelagic systems requires the creation of highly protected areas in remote locations, including on the High Seas, where protection efforts lag.”

Almost all of the large fishes of the pelagic world, including tunas, billfish, and sharks, are highly mobile, and even very large no-take areas have little, if any, impact on these species. There are conservation concerns among large pelagic fishes, especially sharks, but the effective way to rebuild those species is to reduce the catch. If you close large parts of the ocean as the U.S. has done in its Pacific territories, you simply make the boats fish outside the closed areas where they catch just as many fish, including sharks.

In a 2021 paper, Dulvy and co-authors reviewed the extinction risk of sharks and their relatives and found such species are disproportionately threatened in tropical and subtropical coastal waters.

“Science-based limits on fishing, effective marine protected areas, and approaches that reduce or eliminate fishing mortality are urgently needed to minimize mortality of threatened species and ensure sustainable catch and trade of others,” they wrote.

If science-based catch limits cannot be imposed, as is common in tropical coastal waters, MPAs may be the most effective conservation tool. But, for the high seas, where species move great distances and there are already fishing limits in place, MPAs are not going to be helpful in conserving species of concern.