Fishing ban brings species back to Mexico park. But can it rebuild a fishery?

A study finds that a fishing ban at a Mexican marine park – with critical help from local residents – has successfully restored the fish population. Whether it's enough to restore the industry is not clear.

You can sunbathe, go kayaking or windsurfing, or try your hand at diving. No fishing. Period.

That, in effect, is the dictum residents of the tiny village of Cabo Pulmo, at the tip of Baja California, have enforced throughout a 27-square-mile patch of ocean that a decade ago was severely over-fished.

The patch is a national marine park that Cabo Pulmo's residents help oversee. And according to a new study of the impact of that no-fishing policy, fish populations have rebounded beyond anyone's wildest dreams.

The researchers conducting the work say they hope the results will do more than build momentum for more effective enforcement of marine reserves elsewhere in the Sea of Cortez. The research, they say, also highlights the positive effect that residents in comparable areas around the world can have when they buy into the concept of a ban on fishing.

Between 1999 and 2009, total fish biomass – an aggregate figure that accounts for the number and size of fish – grew by more than 460 percent, from roughly 600 pounds per acre to 3,392 pounds per acre, according to a study published recently in the on-line journal PLoS One, an on-line journal of the Public Library of Science.

And species – from top predators to tiny fish that feed on plankton and marine plants – have returned in proportions that resemble those found in ocean ecosystems that have escaped overfishing, signaling a biologically vibrant ecosystem, according to Octavio Aburto-Oropeza, leader of the team that conducted the study.

The only other marine reserve known to have experienced a comparable recovery is Cabo de Polas off of Spain.

For many marine scientists, the concept that no fishing in an overfished area gives stocks a chance to rebuild is a no-brainer, acknowledges Dr. Aburto-Oropeza, a scientist at the Scripps Institution of Oceanography in La Jolla, Calif. But he and his colleagues, whose results were posted Friday on the PLoS website, were stunned at how quickly the recovery took place.

The group did not expect it to happen in a decade, he explains. "It's amazing."

The results are definitely above average, notes Ray Hilborn, a marine ecologist at the University of Washington in Seattle, who was not part of the research team.

He notes that protected marine areas whose fishing restrictions are well enforced typically see stocks rebound by two to three times their pre-protection level.

"The particularly high increase here indicates both that it was severely over-fished" before the no-take zone was set up, and that the enforcement "was particularly good," he writes in an email.

Colleague Tim Essington, another marine scientist at the University of Washington, says he is particularly struck by the breadth of the recovery up and down the food chain.

That aspect "is quite surprising and remarkable," he says, noting that it probably indicates that stocks were severely depleted all along the chain.

While on a broad level the study's observations may be a no-brainer, the work represents the largest no-fishing zone studied to date, as a proportion of the park in which it is found.

After poring over past research results on the subject, the team found that some 80 to 90 percent of the reserves studied to date covered less than three square miles, and most of those covered less than half a square mile.

The 27-square-mile marine park in this study initially included a 13-square-mile official no-take zone – still the largest proportion of no-take zones for any of the 10 marine parks in the Sea of Cortez, Aburto-Oropeza explains. But with government backing, residents of Cabo Pulmo, some 100 strong, opted along the way to enforce the initial fishing ban across the entire park.

Cabo Pulmo National Park's success stands in stark contrast to conditions in nine other marine parks the Mexican government established in the Sea of Cortez between 1937 and 2007. All but one of these reserves have no-take zones. But none of those zones has shown any significant improvement in fish stocks.

Several ecological factors are likely to have contributed to Cabo Pulma's stunning recovery, the team speculates. The entire park is no-take, whereas other parks' no-take zones represent a much smaller proportion of the overall park. And in many of these parks, the no-take zones are fragmented. Cabo Pulmo's reefs remained healthy enough, despite overfishing, to serve as nurseries for young fish. And the park encompasses spawning areas for large predator fish.

But perhaps the most critical element in preventing Cabo Pulmo National Park from becoming a marine reserve in name only (as others have become) is the participation of locals in enforcing the ban – a move that appeared to be profitable to the tiny community.

A study conducted in 2006 showed that the village of Cabo Pulmo's economy pulled in just over $500,000 from its handful of small businesses that cater to vacationers. This gave the residents a per capita income of $18,000 – nearly double Mexico's national figure.

But while the study documents environmental benefits within the no-take zone, and it cites economic benefits for local residents, the researchers have yet to show that the effort can rebuild sustainable commercial fishing – the oft-cited reason for setting up no-take zones in the first place.

Yet this is a crucial step, notes the University of Washington's Dr. Essington.

"Demonstrating benefits to fishing, as opposed to conservation benefits, is always difficult but really important to fully judge the benefits of no-take marine reserves," he notes.

Aburto-Oropeza acknowledges the point, noting that this study was limited to assessing conditions inside the park. The next step is to see what effect the rebound has had on fish populations in surrounding waters.

He finds some encouragement in anecdotal reports from local fishing guides that just outside the park boundaries, visitors have been catching increasing numbers of top-of-the-food-chain fish, such as small tuna, wahoos, and bill fish.

Looking at the "spillover" effect from the park's recovery is one of the next projects on his agenda, he says.