New Study: Mackerel Steals Plankton from Sandeels Skip to content

New Study: Mackerel Steals Plankton from Sandeels

By Iceland Review

The preliminary results of a new study strongly indicate that sandeels in Icelandic waters don’t fatten because of competition over their primary source of food, plankton, with mackerel, which presence in Icelandic waters has increased in the past years.


Archive photo by Páll Stefánsson.

The number of sandeels, on the other hand, has dropped significantly in the same period, which causes problems for seabirds, such as puffins, as they feed on sandeels, Morgunblaðið reports.

“There are two theories as to why sandeels are disappearing,” said Erpur Snær Hansen, biologist and divisional manager of ecology research at the Icelandic Institute of Natural History.

“One concerns the competition over food, that the mackerel eats both the sandeel’s food and the sandeels themselves. Also that the large generation of haddock from 2003 ate a significant amount of sandeel roes.”

“The other theory is that the quantity of plankton changes with warmer ocean temperatures, which causes the sandeels to be more meager,” Erpur explained.

“Our preliminary results indicate that the sandeels aren’t gaining weight. The simple reason for that is that plankton is lacking in the ocean. Someone else is eating the plankton and the most likely culprit is mackerel,” he concluded.

The arrival of mackerel is considered to have a widespread impact on the food chain. The study shows, for example, that gannet has started feeding on mackerel instead of sandeels.

Click here to read more about the condition of seabirds in Iceland and here to read more about mackerel.


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