Bluefin tuna in the Arctic? A sad, but true fish tale

Large bluefin tuna caught along with mackerel offshore  Greenland. Image: Greenland Fisheries. Authority
Large bluefin tuna caught along with mackerel offshore Greenland. Image: Greenland Fisheries.

A research ship’s mysterious catch of three large predator fish off Greenland’s coast is a warning that climate change is heating up the seas and altering the migration of commercial fish stocks.

The biologists and fishermen aboard an Arctic research ship came back with one heck of a fish story.

While fishing and investigating mackerel stocks in 2012 in the strait between Greenland and Iceland, scientists aboard were surprised by the catch of three bluefin tuna, each weighing more than 220 pounds, or 100 kilograms.

The prized bluefin tuna, whose stocks are in decline, are seldom found near Greenland and never that far north.

Bluefin tuna like to gorge on large amounts of small fish and usually search for prey in areas where surface temperatures are warmer than 11° C, according to Professor Brian MacKenzie, lead author of a study from the voyage. The report, by the Center for Macroecology, Evolution and Climate at the University of Copenhagen, was published in the journal Global Change Biology.

Expanded range

At the time of the catch in August of that year in the Denmark Strait, the water was unusually warm and one of tuna’s preferred prey, mackerel, had already expanded into the region.

“The presence of bluefin tuna in this region is likely due to a combination of warm temperatures . . . and immigration of an important prey species to the region. We conclude that a cascade of climate change impacts is restructuring the food web in east Greenland waters.”

Data was too limited to estimate how many tuna swam that far north but the authors believe many more were in the region because bluefins tend to gather in schools of 10 to 100.

“Satellite imagery showing the spread of warm water from the south-east towards east Greenland suggests that recent warming and climate change may have opened a migration pathway from the European shelf towards Greenland for migratory species,” according to the report, which said the fish may have swum to the strait from the north-west Atlantic.

An adult bluefin tuna is typically 1.5-2 metres long but can grow up to 4.5 metres and weigh 650 kilograms. The fish, known for their speed and shaped like a torpedo, are highly prized for sushi, especially in Japan. Last year a bluefin tuna was sold at an auction in Japan for a record $1.6 million, three times the previous year.

Further changes in the migration of commercial fish such as mackerel and herring will mean there will be a need for new fishery and ecosystem management plans, according to the report’s co-author, Helle Siegstad, head of fish and shellfish at the Greenland Institute of Natural Resources.

The Denmark Strait tuna will be further discussed in September at the annual conference of the International Council for the Exploration of the Sea in Spain. – Climate News Network

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