Massive cod assault on Capelin shoal in Atlantic observed
Scientists have observed the largest single act of capelin predation they have ever recorded, according to IFL Science. Over four hours, millions of cod attacked the Capelin shoal mentioned. During this short period, ten million fish perished.
Capelin, or Mallotus villosus, is a small fish that inhabits northern Atlantic waters and feeds on plankton and krill. IFL Science explains that they are important in the food chain, playing a role in the ocean comparable to anchovies in warmer waters.
Threat from predators
Mallotus villosus are vulnerable to predators while searching for spawning grounds. The greatest danger comes from cod, which, during their migration to their spawning grounds, prey on capelin along the way.
An article published in the journal Communications Biology states that MIT scientists, using Ocean Acoustic Waveguide Remote Sensing sonar, detected a gigantic shoal of capelin that extended for dozens of kilometres. According to estimates by Nicholas Makris from MIT, the shoal might have consisted of 23 million fish weighing about 413 metric tonnes.
Capelin did not previously form shoals
Capelin gathered in such a large group to adopt a similar speed and have a common direction in which they move. While shoaling behaviour is known among many fish species, it has never been observed in capelin, according to IFL Science. However, this large concentration of fish makes the capelin shoal an easy target for predators. Scientists calculated that during the observation using the mentioned sonar, approximately 10.5 million capelins were killed.
"In our work we are seeing that natural catastrophic predation events can change the local predator prey balance in a matter of hours," said Makris. According to the scientist, the same is happening with predators. They join forces to attack together, he added.
While the scale of this event is enormous, it does not threaten the capelin population. However, it is significant that rising global temperatures might make some capelin spawning grounds unsuitable, forcing the small fish to concentrate in fewer locations. Then, the risk of predator attacks might increase.
