Plucked from the depths

BORIS WORM, a marine biologist, has spent much of his academic life studying fish. In 2006 he came to the depressing conclusion that by 2048 the world's commercial fisheries would have collapsed. Fish would no longer be on the menu. But Dr Worm is no pessimist and on July 31st he published a more encouraging piece of work in Science. It suggests that, with proper management, it ought to be possible to rebuild the world's fisheries.

Dr Worm, who works at Dalhousie University in Nova Scotia, Canada, conducted the study in collaboration with Ray Hilborn of the University of Washington, Seattle, who was a ferocious critic of his initial analysis. For two years the pair, along with 19 colleagues, gathered data from ten of the world's large fisheries. They found a mixed picture, in which some species were overfished in some places and not in others.

AFP

What gave Dr Worm and Dr Hilborn cause for hope was that, in five of the ten fisheries, steps taken to curb the damage were beginning to pay off. They drew this conclusion because exploitation rates (the proportions of available fish caught) in these areas were falling. The researchers examined eight management techniques used to rebuild fisheries, including closing certain areas to fishing, limiting the catch permitted and restricting the gear used to haul fish from the sea. They concluded that although the details varied with the local context, a combination of catch quotas coupled with strategic measures aimed at specific species, such as using certain types of fishing nets whose shape and mesh size are designed to catch only certain sorts of fish, usually worked best.

The researchers also recommend that the “maximum sustainable yield”, an internationally agreed measure of how much can be taken from a fishery, should be thought of as the upper limit on exploitation rates rather than as a target. Their analysis suggests that fishing a little below this level is the most efficient way of ensuring a sustainable income.

The same issue of Science also reports a second optimistic fisheries-related study. This looked at the restoration of oyster beds in Chesapeake Bay, an inlet that lies between Maryland and Virginia, in the United States.

Previous attempts to boost the numbers of native oysters in the bay by banning oyster fishing had proved disappointing because the molluscs failed to re-establish themselves. However, Romuald Lipcius of the College of William and Mary, in Gloucester Point, Virginia, and his colleagues, did succeed in boosting the number of native oysters. In fact, they report the largest restoration of native oyster numbers anywhere in the world.

The researchers constructed oyster reefs in nine protected sanctuaries on the Great Wicomico River, which flows into Chesapeake Bay. Instead of just piling the oysters up close to the riverbed, as had been done in the past, they built reefs of various heights above the bed for them to grow on. After three years, they found five times as many oysters living on reefs that stood high in the water as were on the lower-lying reefs. Altogether, there were 185m of the molluscs. Dr Lipcius thus suggests that creating high-standing artificial reefs could help with restoration projects elsewhere—and the two groups of researchers together have shown that it is possible, if you try, to pluck both fish and molluscs from the depths of despair.