Marine protected areas are the oceanic versions of national parks: In the most stringently protected regions, fishing and other extractive activities are banned. Some critics in the fishing industry have long argued that such restrictions negatively affect fishers by reducing catches and forcing mariners to travel longer distances to fish. However, researchers have now analyzed maritime data to show that’s not true, at least for North America’s largest marine protected area. Their results were published in Science Advances.
Protect What’s Left
In late 2017, Mexican officials established a 148,000-square-kilometer marine protected area, Revillagigedo National Park, in the Pacific Ocean off the southern tip of the Mexican state of Baja California Sur. At the time, Fabio Favoretto was attending graduate school in the state’s capital, La Paz. The marine ecologist, who now splits his time between the Centro para la Biodiversidad Marina y la Conservación in La Paz and the Scripps Institution of Oceanography in La Jolla, Calif., remembered feeling excited that such a large swath of the ocean—roughly the size of New York State—was being safeguarded for the future.
The ocean was once viewed as limitless in its bounty, Favoretto said. However, massive fishing operations have already depleted fish stocks in many coastal regions, he said. “We’re seeing this push toward the high seas.” Establishing places such as Revillagigedo that are fully protected against fishing allows marine life to recover, Favoretto explained. “It’s a way that we can protect what we have left.”
Investigating Claims with Data
But marine protected areas haven’t been embraced by everyone. In the case of Revillagigedo National Park, the Mexican fishing industry was outspoken about concerns that the park would have detrimental effects on mariners and result in, for example, decreased catches. Favoretto and his colleagues decided to investigate the veracity of those claims using data.
The researchers amassed records from the Mexican fishery commission for over 200 vessels that were permitted to catch tuna, sharks, or swordfish. Favoretto and his collaborators focused on two time windows that straddled the creation of Revillagigedo National Park—2008–2017 and 2018–2021—and compared metrics such as the duration the vessels spent fishing, their reported catches, and the area they traversed.
The team started by defining a quantity called “catch per unit of effort,” which has units of metric tons of fish caught per day. It’s necessary to consider not only the amount of fish caught but also the time spent fishing, Favoretto said. “You can catch three tuna in 4 days, or you can catch three tuna in 1 hour. It’s very different.” (The researchers used information about a vessel’s speed to infer when its mariners were likely fishing or searching for fish.)
When Favoretto and his colleagues compared data from before and after the creation of Revillagigedo National Park, they found no significant change in catch per unit of effort. That’s clear evidence that fishers’ productivity didn’t decrease because of the marine protected area, the team concluded.
Next, the researchers examined vessel-monitoring data that recorded, on an hourly basis, the geographic coordinates of each fishing vessel. Favoretto and his collaborators used that information to determine the approximate area traversed by each vessel during fishing activities. Critics of marine protected areas have suggested that the preserves force mariners to travel over larger areas to fish.
When the team compared the footprints that the vessels traversed before and after the creation of Revillagigedo National Park, they found that the fishing industry’s concern wasn’t borne out: Vessels, on average, fished over a smaller geographic region after 2017 compared with before. And the difference was statistically significant—mariners tended to traverse a roughly 50% smaller swath of the ocean after the marine protected area was established.
One explanation for that finding, the researchers proposed, is that in recent years fishers have tended to focus on fishing farther from the land. “Our interpretation is that they are concentrating the same effort in a smaller, more-productive area in the high seas,” Favoretto said. That’s in part because regions closer to shorelines are often overfished, he said. “Coastal areas are depleted.”
Overall, the creation of Revillagigedo National Park did not adversely affect catches or the area that fishers had to traverse to collect those fish, the researchers concluded. That may be true, said Tim McClanahan, a conservation biologist for the Wildlife Conservation Society in Mombasa, Kenya, who was not involved in the research, but the investigation didn’t address other potential issues that fishers have raised about marine protected areas.
For example, do marine protected areas prompt some fishers to leave fishing entirely? The number of hours that vessels spent fishing within the footprint of Revillagigedo National Park had been steadily declining for a decade before the park was established, Favoretto and his colleagues showed. “That seems to suggest that people were not making a lot of money,” McClanahan said. Fishers that were struggling financially might have opted to seek employment on land when they heard that the park was being established, he said. The data that the team analyzed don’t reflect how many people might have left fishing, said McClanahan. “Poverty is a loud voice.”
—Katherine Kornei (@KatherineKornei), Contributing Writer