Read our COVID-19 research and news.

Easily spotted. Coral trout have increased in size and number after marine reserves were enlarged on the Great Barrier Reef.

Leonard Low

Marine Reserves Help Fish Recover

SAN DIEGO—When fisheries have plummeted or collapsed, one approach to fix the situation is to set up a marine reserve where fishing is banned. The idea is to provide relief to stressed fish stocks by providing safe habitat where fish can reproduce, and then spread out. But banning fishing when a fishing industry is already struggling can be controversial. Yesterday and tomorrow, at two sessions here at the annual meeting of the American Association for the Advancement of Science (which publishes ScienceNOW), researchers presented new data that marine reserves help fish recover.

Jennifer Caselle, a biologist from University of California, Santa Barbara, provided a local example of success. In 2003, the state of California set up a network of 12 marine reserves near Los Angeles and banned fishing in more than 488 square kilometers. By monitoring the area before and after, Caselle and her colleagues found that over 5 years there were 50% more blue rockfish and other species targeted by fishing inside reserves than outside, and that their biomass was 80% higher. There was no change in species that people don't eat, suggesting that fishing restrictions were responsible for the recovery.

Another success story comes from Australia, which created the first large marine reserve in the Great Barrier Reef Marine Park in 1975. After a major die-off of coral, the government decided in 2003 to rezone the park and increased the proportion of no-take areas from less than 5% to 32%. Many fish species quickly doubled in size and numbers. Biomass of coral trout, for example, doubled within 2 years, after fishing was banned on heavily fished reefs. The new reserves also seemed to improve ecosystem health in general, as outbreaks of coral-eating starfish were nearly 4 times more frequent on the reefs where fishing was still permitted. It's not clear why, however.

Fears of a collapse of recreational fishing in the park proved unfounded. The researchers, led by Laurence McCook of the Great Barrier Reef Marine Park Authority, in Townsville, found that the number of fishing licenses continued to rise after the rezoning.

But not everything is rosy, especially for large animals such as turtles and dugongs, whose populations continue to drop. "The biggest failure of the Great Barrier Reef park is the decline of megafauna," said coauthor Terry Hughes, a coral reef biologist at James Cook University, Townsville. These species migrate in and out of the park boundaries, so there is a proposal to extend the park east into the Coral Sea.

The situation in the Great Barrier Reef is consistent with the results of a larger analysis, led by Russ Babcock of the Commonwealth Scientific and Industrial Research Organization in Cleveland, Queensland. Looking at marine reserves in New Zealand, Australia, California, the Philippines, and Kenya, the team found that species targeted by fishing—after they became protected by the reserve—started to respond faster than others. Those that had been fished began to increase in abundance after 5 years, on average, compared to 13 years for other species that are indirectly affected by the reserve (such as urchins that are eaten in greater numbers by the recovering fish). "Marine managers will have to sustain confidence in the potential for restoration outcomes for considerable lengths of time before they can expect… the recovery of the broader ecosystem as well as target species," the authors conclude.

What makes a marine reserve successful? Taking a broad look at 56 marine reserves around the world, Joshua Cinner of James Cook University in Australia examined the social and economic factors. The number of people living near the reserves played a big role in some cases. In the Caribbean, reserves near large populations tended to have less fish relative to unprotected areas than did reserves that were more remote. But the opposite was true in the Western Indian Ocean. It's not clear why, but one reason could be that people tend to move to places with healthy marine reserves so that they can fish nearby. (No pattern could be found in the Philippines.)

Another factor related to successful marine reserves was, as expected, compliance with fishing restrictions. And that tended to be associated not just with enforcement, but more complicated social dynamics such as how well people work together and participate in research and management. "In areas where people work together to invest in their resources, we saw less poaching inside marine reserves," Cinner said in a statement. "To get high levels of compliance with reserve rules, managers need to foster the conditions that enable participation in reserve activities, rather than just focusing on patrols."

The results of these and related papers also appear tomorrow in a special issue of the Proceedings of the National Academy of Sciences.