Research led at the University of Strathclyde suggests that predatory seals are constraining the recovery of cod stocks in Scottish West coast waters.

The study found that seals are eating up more than 40% of the total cod stock

The study found that seals are eating up more than 40% of the total cod stock. Credit: Mick Garratt/CC BY-SA 2.0, via Wikimedia Commons

Grey seals are believed to consume nearly 7000 tonnes of cod each year off the west of Scotland, where landed catches now amount to only a few hundred tonnes.

In an effort to protect the stock, the EU Cod Recovery Plan places strict regulations on the amount of time spent at sea by fishermen and the quantity of cod they can land. However, the plan does not take into account the amount of cod eaten by seals, which appears to be a major reason why the strategy in the West of Scotland has had little success so far.

Dr Robin Cook, a Senior Research Fellow in Strathclyde’s Department of Mathematics & Statistics, led the study. He said, “Fishery managers face striking a difficult balance. 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.”

Grey seal populations increased significantly around the British Isles after the passing of UK conservation laws in the 1970s but, more recently, their numbers in the West of Scotland have levelled off at around 30,000-40,000. They eat a wide range of fish, with sand eels forming the largest part of their diet.

Although cod form only around 10% of the total weight of fish eaten by seals, this is sufficient to have a significant impact on the stock.

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