Piscivorous fish patrol krill swarms

Dense swarms of the krill Meganyctiphanes norvegica in the Norwegian Sea were patrolled by large, piscivorous fish, which apparently use the krill swarms as feeding grounds in their hunt for planktivores. For the krill, patrols of piscivores may add to the generally accepted anti-predator benefit of the swarming behavior. The fact that krill swarms govern small-scale patchiness of large piscivores emphasizes the key role of krill in oceanic ecosystems.