Beneath the Californian waves lurks a grisly gauntlet, patrolled by tentacled predators with a voracious appetite that will eat anything they can grasp hold of – including each other. Though squid cannibalism has been suspected for some time, until now it had never been observed in the wild.
Squid remains had previously been found in the stomachs of other members of their kind, while others had been seen eating each other when trapped in fishermen's nets, although marine biologists believe this may be an unnatural behavior driven by the panic of being snared. However, reporting their discovery in the journal Deep Sea Research Part I: Oceanographic Research Papers, the study authors describe how they used remotely operated vehicles to spy on squids living in the Monterey Submarine Canyon, finally catching the deep-sea enigmas in the act.
More than 100 individuals belonging to the genus Gonatus were observed, with many of these seen engaging in cannibalism. In particular, the species Gonatus onyx appeared to have developed a taste for its own brethren, with 42 percent of its prey made up of squid. Another species, Gonatus berryi, was also seen engaging in cannibalism, though to a slightly lesser extent.
The researchers believe the main reason for this is probably related to the energy demands of these squids. The species observed have one of the highest metabolic rates of all cephalopods, and because females spawn only once in their lifetime, they have to invest a high amount of energy into their egg mass.
Gonatus onyx squid eating another squid of the same species. 2010 MBARI
As such, they are thought to prey on other squid, in addition to fish, as this enables them to build up a larger store of nutrients. This comes in particularly handy during their nine-month brooding period shortly after spawning, when they do not hunt at all and have to rely on their existing energy reserves.
Observing the animals’ behavior, the study authors describe them as “versatile, opportunistic predators,” willing to eat anything they can, and using their hook-lined tentacles to grab hold of their prey as they devour it.