No more seafood by 2050?

There may be no more commercial fish stocks left in the sea by 2050, according to a new study cataloguing the global collapse of marine ecosystems.

It blames not just over-fishing, but also mankind's wider attack on the health of ocean ecosystems, for instance from pollution. "Unless we fundamentally change the way we manage all the ocean species together, as working eco-systems, then this century is the last century of wild food," says Steve Palumbi at Stanford University in California, US, who carried out the four-year investigation with colleagues.

The study is the biggest and most all-embracing effort yet to understand the productivity of the oceans and predict their future. Uniquely, it combines historical data on fish catches, some of it going back a thousand years, with analysis of marine ecosystems and experiments to bring marine life back to protected areas.

The authors, from five countries, reviewed hundreds of individual studies covering every scale from whole oceans to marine plots of a few square metres. They say the same pattern emerges at every scale. Rich ecosystems with many species can survive over-fishing and other threats well - but once biodiversity is lost, the entire system, including fish stocks, goes into exponential decline.

Accelerating pace

A healthy ecosystem keeps fish healthy and well fed, and maintains fish nurseries such as coral reefs and seagrasses. But there are fewer such healthy systems each year. Since 1950, 29% of commercial fish species have suffered collapse (defined as a loss of 90% or more).

And the pace is accelerating. The study extrapolates that the last currently commercial fish species will be lost in 2048.

But the report also points out that the vulnerability of fish stocks to collapse depends on overall biological diversity. Areas of ocean with low biodiversity have suffered collapses to 34% of commercial fish stocks, compared to 24% in those areas with high biodiversity.

Many fisheries scientists have been sceptical of the idea that damage to a few non-fish species could be a threat to major fish stocks. But this study demonstrates, for the first time, that commercial and ecological health go together in the ocean. "Every species matters."

Health and wealth

Ecologists are heralding the findings as a breakthrough not just for the study of the oceans, but also more widely for gauging the value of natural ecosystems to the health and wealth of the planet. "This analysis provides the best documentation I have ever seen regarding biodiversity's value," says Peter Kareiva at the Nature Conservancy in the US.

The good news is that fish stocks can recover if ecosystems are protected and biodiversity revives. Boris Worm, a marine conservationist at Dalhousie University in Halifax, Canada, who led the study, says that inside the 44 protected areas studied, "species came back more quickly than people anticipated - in three or five or 10 years. And where this has been done we see immediate economic benefits."

A typical marine conservation project can increase biodiversity by more than one-fifth and raise fish catches four-fold, the study showed. Even so, less than 1% of the global ocean is effectively protected right now.

"Marine biodiversity provides lots of services to the planet besides fisheries - such as preventing algal blooms, processing waste and maintaining the ability of the oceans to absorb our carbon dioxide emissions," says team member Nicola Beaumont at Plymouth Marine Laboratory in the UK. "To help minimise climate change we need a resilient and healthy marine ecosystem," she adds.

"Biodiversity conservation and long-term economic development must be viewed as inter-dependent," the researchers conclude. Or, as Worm puts it: "The oceans define our planet, and their fate may to a large extent determine our fate."

Journal reference: Science (vol 314, p 787)

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