The world’s fish might not be doomed after all, according to a report this week. But that doesn’t mean we can relax as, paradoxically, the little, fast-growing fish that we thought were safe may be nothing of the sort.

The first analyses of massive databases of global fisheries statistics assembled in the past decade suggested that if we continued to fish at current levels we would destroy all fish stocks by 2048. While a later study found some stocks were stable – most still seemed to be overfished.

Now Trevor Branch of the University of Washington in Seattle and colleagues report that this prediction was also too pessimistic, because it assessed the state of stocks based on catches, rather than how many fish there are in the sea.

It is expensive to measure a fish stock directly using the age and size of fish, and other features, so most are assessed indirectly using catch records: lower catches are taken to mean fewer fish. But even when stocks are thriving, catches can also fall due to fishing restrictions, poor records or pricey boat fuel.


Branch’s team found that catch records suggest 68 per cent of world stocks are overfished or have collapsed altogether. But only 28 per cent of the stocks that could be assessed using biomass estimates from scientific stock assessments were overfished or had collapsed. It wasn’t just that the scientifically assessed stocks happened to be healthier: the catch data for these stocks showed the same pessimistic pattern typical of catch data in general.

Dip but no collapse

One problem is that the catch method always defines certain dips in catches as a sign of collapse. They may not be: the method decided that the team’s computerised fisheries model had “collapsed” even when it hadn’t.

The revised forecast doesn’t mean there’s a lot more fish to be had, warns Branch. “Most fisheries are already being caught at or near the maximum sustainable level.” Some are still overfished or have collapsed, and they all need management based more on stock measurement than catch data. But at least most of the world’s fisheries do not, yet, appear to be headed for destruction.

Except where we least expect it. Biologists have always assumed fast-growing, fast-reproducing fish low on the food chain, such as anchovies, are less susceptible to over-fishing than slow-growing predators such as cod. A related study this week found that unexpectedly, they may be even more susceptible. This is bad, as the little fish feed many other species.

They may be vulnerable partly because they are considered stable, so get little management and research. Taken together, the studies show more scientific stock assessments are desperately needed, says Branch. “Why doesn’t the UN Food and Agriculture Organization buy a fleet of vessels to survey the waters of developing countries? It would definitely be worth it.”

Journal reference: Scientific fish stock study: Conservation Biology, DOI: 10.1111/j.1523-1739.2011.01687.x; fast-growing fish study: Proceedings of the National Academy of Sciences, DOI: 10.1073/pnas.1015313108