Large patches of ocean that countries have declared out of bounds for fishing have become gold standards for maintaining or rebuilding the health of tropical reefs and other key ocean habitats.
A new study suggests that less draconian restrictions could put many troubled reefs on the road to recovery. A mix of approaches – from curbs on the type of fishing gear used and clearly defined fishing rights to restrictions on the species of fish caught – also can lead to healthier, more resilient reef communities, the study suggests.
The recovery probably would take longer under such management practices than it would under a flat ban on fishing, the researchers acknowledge. And the long-term effects of ocean acidification and global warming remain wild cards.
But the scientists say that more flexible management practices could reduce friction between conservationists and the millions of people, particularly those living in developing countries, who depend on the reefs for their livelihood. The hope is that management plans tailored to local needs will be less likely to force a Hobson's choice between long-term conservation goals and immediate livelihoods.
"Conservation is not just about walling off areas and denying access, it’s about finding effective solutions that preserve the integrity of the ecosystem," notes Aaron MacNeil, a marine ecologist at the Australian Institute of Marine Science in Townsville, Queensland, and the lead author of the study, which is set to appear in Thursday's issue of the journal Nature.
Conservation groups have done a lot of heavy lifting in making the case for marine-protected areas and in showing that they can work, he writes in an e-mail.
But, he adds, "fisheries closures are not for everyone, and if they are established in places where people are poor or disinclined to comply with regulations, then they just become ‘paper parks.’ "
The new study, involving researchers from Australia, Canada, Britain, and the United States, provides a unique perspective on tropical-reef conservation that can help inform regulations that are more likely to get buy-in from local people than an outright ban, he adds.
Based on fisheries data from 832 reefs in 64 locations around the world, the study suggests a global base line from which to gauge success. It shows how fish biomass at the reefs stacks up against the base line. It estimates the time needed for a fully protected reef to return to normal. And it suggests how quickly fish biomass can bounce back if measures other than fishing bans are used.
Few question that the world's tropical-reef ecosystems – the ocean analogue to tropical rain forests and their biodiversity – are in trouble and that for now, fishing remains the dominant threat to reef ecosystems.
On average, an unfished reef system supports about 1,000 kilograms (1.1 tons) of fish per hectare (two acres), found the team, which adopted that as their base line.
A healthy reef system typically hosts at least 90 percent of that base line, the study shows. With the right mix of species, a reef system can still maintain its full range ecosystem functions with about 500 kilograms of fish per hectare.
But of the 832 reefs in the study, 83 percent had fish densities below 500 kilograms per hectare. One-third of the reefs fell below 250 kilograms per hectare. Reefs around Guam and Papua New Guinea were in the worst shape, with only 10 percent of the fish-density base line – a level at which the reef system has all but collapsed.
The team's analysis found that for reefs where fishing was permitted or under some restrictions, on average it would take 39 years for fish density to recover to the 90 percent level. The worst reefs could take up to 60 years to recover.
Meanwhile, previous studies have suggested that marine-protected areas, which have been set up during the past 20 years, also take decades to bring fish populations back to the base line.
One key finding in the new study: Fish that graze on algae – vital to preventing algae from smothering a reef – don't need to be present at "pristine reef" levels to fulfill their roles as reef cleaners. They tend to reach their ideal biomass well before the overall fish density on a reef reaches the 500 kilogram-per-hectare mark. That may help explain a reef system's ability to maintain its functions with only half the fish density of an unfished reef.
In general, reefs with some form of fishing restrictions sported fish biomass levels averaging 27 percent higher than those of fished reefs. Where those restrictions involved nets hurled from beaches or the catch of algae grazers, the density of grazers in general increased to about 80 percent of the levels needed to keep algae in check.
For Nicholas Dulvy, a marine biologist at Simon Fraser University in British Columbia whose conservation research focuses on sharks and rays, any surprise from the study comes less in its results than in the effort it makes to evaluate, at least in broad terms, more-traditional conservation approaches, rather than focus on marine-protected areas alone.
Over the past decade, he says, many marine scientists and conservations groups "have given up on fisheries management and instead focused on locking down the ocean into marine protected areas," he writes in an e-mail.
Yet even for marine-protected areas, accommodations are being made for some level of fishing, notes Deborah Brosnan, an independent marine biologist who works closely with governments in developing conservation and natural-hazard resilience plans.
Last summer, researchers at the University of Queensland in Australia published an analysis of several approaches to setting up marine-protected areas in an attempt to strike a balance between long-term conservation demands and those of local residents for immediate income from fishing. Depending on local circumstances, the approaches involved gradually increasing the size of a reserve, increasing the number of species protected, or adjusting the number of months a year that the reserve would be closed to fishing.
The latest study provides additional information that managers could use immediately, notes Dr. Brosnan.
"In communicating with fishermen, being able to provide an explanation with biomass numbers will be critical to explaining the level of degradation and the goals of recovery in a language that they can understand," she writes in an e-mail. This kind of communication "also will be important to help avoid a situation where the recovery of some fish triggers overfishing."
She currently is advising an agency that is having a hard time explaining to fishing interests why tighter reef-fishing restrictions are needed. The issue is raising "real tensions," she writes. The kind of information the new study provides "gives a rationale, a basis, and a way to have a dialogue instead of a conflict."