Fisheries 
warned 
against 
reliance 
on prawns

As stocks of big fish have dwindled, fishermen have turned to smaller fry to provide their main source of income.

The removal of natural predators from the sea has seen catches of prawns, scallops and lobsters rocket around the world.

In many regions, including the UK, shellfish are now the most valuable marine resource. But replacing fish such as cod and haddock with prawns and scallops is a highly precarious strategy, according to the authors of a new study.

Like simplified agricultural systems, shell-fisheries are said to be unstable and at great risk of collapse from disease, species invasion and climate change.

Lead researcher Leigh Howarth, from the University of York, said: “Prawns are now the most valuable fishery in the UK, with catches currently worth over £110m a year.

“But this fishery has come to exist only after we over-exploited populations of cod, haddock and other predators. If shellfish now collapsed the social consequences for fishermen would be devastating. There are simply very few remaining species left to target.”

The study, published in the journal Fish and Fisheries, reports a similar situation all over the world.

In the US and Canada, lobster, catches of scallops and crab have replaced those of cod.

Meanwhile in the Black Sea, Baltic and of the west coast of Africa, over-fishing of large predators has caused ecosystems to be overrun with jellyfish. This has led to severe oxygen depletion and excess levels of hydrogen sulphide which are wiping out important food chains across 100,000 square kilometres of the sea floor, said the researchers.

Co-author Professor Callum Roberts, also from the University of York, said: “The rise of shellfish has been welcomed by many as a lifeline for the fishing industry. However, such changes are not a result of successful management, but rather a result of management failure, a failure to protect stocks and their habitats in the face of industry innovation and over-fishing.

“This study highlights why the UK needs to urgently act to protect our seas. We need more marine protected areas to stop our seas from becoming a wasteland and to restore the diversity and productivity of fisheries well into the future”.