Rising sea temperatures combine with over-fishing to threaten North Sea cod

Researchers in the UK believe that higher temperatures during the first half of recent years have reduced North Sea cod breeding rates. They argue that the rise in sea temperature may be combining with over-fishing to threaten the future of the fish.

Scientists at the Centre for Environment, Fisheries & Aguaculture Science (CEFAS) in Lowestoft, England have published their findings on North Sea cod stocks in the 9 March edition of Nature. They argue that noticeably lower year-classes – fish spawned in a specific year – have followed warmer seasons. “Cod in the North Sea are near the southern boundary of their range and, historically, strong year-classes have been associated with lower-than-average temperatures,” states the article.

1996 was the last year that lower-than-average temperatures in the North Sea were recorded. Since 1996 spawning rates have dropped in accordance with the higher sea temperatures, says the researchers.

The impact of higher sea temperatures and continued over-fishing mean that there is increasing pressure to reduce the legal quota for North Sea cod catches. The authors of the study published in Nature suggest that the North Sea cod quota should be reduced by 40 to 60%. The International Council for the Exploration of the Sea also backs such a cut in the quota.

CEFAS staff conduct a ‘trawl survey’ of the North Sea annually during August/ September. They catch fish that are members of ‘commercially important species’ to determine age composition. The information is used to determine overall fish stocks in the North Sea.

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