Published online 12 August 2011 | Nature | doi:10.1038/news.2011.479

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Marine protected area sees fish increase fourfold, sharks tenfold, in a decade.

Cabo Pulmo's fish population is booming because the locals have switched from fishing to ecotourism. O. Aburto-Oropeza

At conferences, Grant Galland calls the marine protected area he works on in Cabo Pulmo in Mexico the "best in the world".

"I do it in part to see if anyone challenges me or shows me one that has been more successful," says Galland, a marine ecologist at the Scripps Institution of Oceanography in La Jolla, California. So far, he says, no one has.

Cabo Pulmo National Park covers just 71 square kilometres — a little bigger than Manhattan — at the southern end of the Baja California Peninsula. In PLoS One this week1, a team including Galland reports that fish biomass in the marine protected area (MPA) increased more than fourfold between 1999 and 2009.

Fish biomass elsewhere in Mexico, including in other marine protected areas with weaker enforcement, didn't improve at all over the same period.

The area owes its success, says Galland, to the efforts of one local family that campaigned for the reserve's creation in 1995 and is devoted to policing it. The family used to be fishers, but decided it would be better to preserve their ecosystem and make a living from tourism, says Galland.

They now watch for boats and head out to deter them from fishing. "They're like vigilantes," says Galland. Although just 35% of the park is designated as 'no take', the local population of about 100 villagers follow a no-fishing policy for the entire reserve, says study leader Octavio Aburto-Oropeza, also of Scripps.

Five locally owned tourism businesses in Cabo Pulmo pull in enough money to earn their 30 employees an average of US$18,000 per year, compared with the Mexican average of around $15,000. "If you can make more money doing tourism, that unlocks the real benefit of an MPA. You genuinely have a win-win situation on your hand," says Peter Jones, a marine biologist turned human geographer at University College London, UK, who studies how to make effective marine reserves.

Shark infested

Aburto-Oropeza's team found an average 463% increase in the number of fish in Cabo Pulmo. Top predators such as sharks fared best: their biomass went up more than tenfold, perhaps because they are drawn to the area by all the fish, or perhaps because the reserve is a good breeding ground.

The percentage recovery isn't unprecedented – one recent study found an average of 446% in 55 MPAs2. But the density of fish living on the park's reef, at 4 tonnes per hectare, is the best the authors have seen anywhere on record.

The recovery at Cabo Pulmo seems to be "exceptionally good" agrees Peter Sale, Assistant Director of the United Nations University Institute for Water, Environment and Health, who is based in Port Carling, Ontario, Canada.

The divers also noticed Cabo Pulmo fish doing strange things. On most Mexican reefs, a scale-eating blenny (Plagiotremus azaleus) sneaks up on its prey by hiding amid schools of hundreds of similar-looking but harmless Cortez Rainbow Wrasse (Thalassoma lucasanum). But Cabo Pulmo's blennies hunt in packs of several hundred. "They terrorize the other fish," says Galland. This behaviour has not been seen anywhere else3.

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Such changes highlight the possibility that a reserve may not return to its pristine state. "We don't know if it's returning to normal or turning into something else," says Galland.

The recovery shows that even small reserves can allow fish populations in the Gulf of California to recover, say the authors. But they add that the area is under threat from the development of a resort aiming to house thousands of tourists and a marina just a few kilometres to the north.

Galland and others are now working to compile environmental data, such as the direction of prevailing ocean currents, in an effort to quantify the probable impact of the resort and petition against its development.