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Dwindling Cod Populations May Be Caused By Grey Seals Says Study

18 May 2015, 8:01 am EDT By Ted Ranosa Tech Times
Researchers from the University of Strathclyde have discovered that the significant decrease of cod stocks found in the west coast of Scotland is potentially caused by the rapid increase of grey seal populations in the area.  ( Mats Hagwall | Flickr )

Latest study by the University of Strathclyde has revealed that grey seals are responsible for the decrease in local cod stocks in the west coast of Scotland.

Researchers from the university discovered a significant increase in grey seal population in the area after the approval of several conservation laws in the 1970s. The number of seals in Scotland's west coast is estimated at around 30,000 to 40,000.

It is believed that these local grey seals consume around 7,000 tons of cods annually, inadvertently causing the recovery of cod stocks to be drastically affected.

Fishermen in the Atlantic have long blamed seals as the reason for the rapid decline of cod stocks and several studies have been conducted to verify this accusation.

In an effort to speed up the recovery of cod population, the Canadian Senate passed a controversial plan to systematically kill off 70,000 grey seals in the Gulf of St. Lawrence through a bounty system.

This move, however, has been objected by marine experts who claim that no credible scientific evidence can prove that the mass killing of the grey seals would have its intended result.

Senior Researcher Dr. Robin Cook of Strathclyde's mathematics and statistics department explained that while fishing has played a role in the diminishing number of cods, the predation by the grey seals has prevented the stocks of fish from recovering.

"Fishery managers face striking a difficult balance," he said. "With high predation by seals, the cod stock will struggle to improve and the recovery plan may not deliver the expected results. We may have to live with smaller cod stocks if we want to protect our seals."

Cook added that when the stocks of cod decreased to about five percent of what they were in 1981, the European Union launched a recovery plan to allow the fish to recover. Despite this, experts were only able to see modest improvements in the situation off the west coast of Scotland.

Before the implementation of the EU recovery plan, fishing accounted close to 50 percent of the total weight of the cod stock in the affected areas, but it fell to about half of it after the plan was launched.

Predation by the grey seals, however, rapidly increased during this time. The animals consume around 40 percent of the total weight of stocks.

Dr. Steven Holmes, a member of the European Commission Joint Research Center and co-author of the report, said that the grey seals could continue to consume the cod in Scotland's west coast even though the stocks of the fish are quite low.

The University of Strathclyde study is published in the Journal of Applied Ecology.

Photo: Mats Hagwall | Flickr

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