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#Science

Predatory grey seals pegged as a hurdle in Scottish cod stock recovery

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Though loss of cod owing to fishing and natural causes isn’t a new thing for the Scottish coasts, one of the major reasons behind constrained recovery of cod stocks in Scottish West coast waters in recent years is presence of predatory seals, a research led by the University of Strathclyde suggests.

Fishing has been responsible for removal of almost 50 per cent of cod from the coastal waters, but recent decline in cod stock is a direct result of predatory activities of grey seals. Though fishing in the region has been halved in recent years, predatory seals have capitalised on decrease in fishing and have eaten up more than 40 per cent of the total stock.

According to some estimates, grey seals consume nearly 7,000 tonnes of cod each year off the west of Scotland as compared to fishing which only amounts to a few hundred tonnes.

Dr Robin Cook, a Senior Research Fellow in Strathclyde’s Department of Mathematics & Statistics, revealed that the current cod stocks have plummeted to just 5 per cent of the value they had in 1981. Despite the recovery plans aimed at curbing fishing, cod stock recovery have shown few signs of improvement. Cook added that though fishing played an important part in reducing the cod stock, grey seals are now playing their part by preventing the recovery.

As far as EU’s cod stock recovery strategy goes, it only places strict regulations on the amount of time spent by fishermen at sea and the quantity of cod they can land. One major gap in the strategy is that it doesn’t take into consideration the amount of cod consumed by seals and that could be one of the major reasons why EU’s strategy hasn’t garnered any success.

Dr Cook adds: “With high predation by seals, the cod stock will struggle to improve and the Recovery Plan may not deliver the expected results”.

Dr Steven Holmes, of the European Commission Joint Research Centre – co-author of the report – added that grey seal population has increased on the West Coast of Scotland in recent years and one of the major reasons could be that they are able to find the cod just as easily despite dwindling stock.

“This makes the remaining stock very vulnerable to predation”, Holmes adds.

Most recent statistics reveal that grey seal numbers stand at around 30,000-40,000 in the West of Scotland and though cod account for just 10 per cent of total weight of fish eaten by seals, this amount is sufficient to significantly impact cod stock.

The research paper has been published in the Journal of Applied Ecology.