
A group of American and Norwegian oceanographers recorded the largest attack of predators in known history. The events unfolded in the North Atlantic Ocean off the coast of Norway at the height of capelin spawning. The study was published in the scientific journal Communications Biology (CommsBio).
Billions of capelin migrate each year in February from the edge of the Arctic ice sheet to the Norwegian coast to throw eggs. At the same time, the capelin’s main enemy, the Atlantic cod, congregates there.
In the new work, the team captured the interactions between cod and capelin populations over a vast area. To do this, the scientists used a broadband acoustic imaging technique.
The observations showed how capelin began to cluster into a huge shoal of about 23 million individuals, covering tens of kilometres. In response, cod also began to gather in a flock of 2.5 million heads. When the predators caught up with their prey, an epic hunt took place underwater, during which the cod ate more than 10 million fish, or more than half of the capelin shoal.
The dramatic encounter between cod and capelin was the largest predator attack ever recorded, both in terms of the number of individuals involved and the area over which the event occurred.
Scientists noted that the capelin population suffered very little loss from the cod attack, as the affected herd represents only 0.1 per cent of capelin spawning in the region.
However, as climate change causes the Arctic ice sheet to retreat, capelin will have to swim a greater distance to spawning grounds. This makes the species more vulnerable to predators.