These squids are fierce predators, but caring mothers.

In the ocean’s twilight zone, squids are dominant predators. Two long tentacles with thick clubs at the tip grab a meal, then eight arms lined with suckers hold on tight. The armhook squids (family Gonatidae) have a secret weapon to keep especially slippery prey from escaping their grip: Tiny claws line their arms to prevent prey from wiggling loose. The sharp hooks can pierce the scales of a fish or the squishy tissue of a squid. They also help immobilize prey bigger than the squid themselves.

We frequently encounter armhook squids during our explorations of the midwater in Monterey Canyon. The black-eyed squid (Gonatus onyx) is the most common. We have encountered other stunning armhook squids—the deep-red Gonatus berryi, the fiery-white Gonatus pyro, the eight-armed Gonatopsis, and the small-finned Berryteuthis.

Until recently, the diet of the armhook squids in the genus Gonatus remained unknown. Our archive of thousands of hours of underwater video contains valuable observations of feeding interactions of deep-sea animals, including squids. Taking a closer look revealed that fishes were a favorite food. But we also saw a surprising pattern: Both Gonatus onyx and Gonatus berryi frequently feed on their own kind. 

These squid have an active metabolism, which demands food for fuel. Food is scarce in the deep sea, so a hungry Gonatus cannot afford to be picky. Dining on their own kind also reduces competition for food and mates.

In the endless expanse of the ocean’s midwater, finding food is not the only challenge facing armhook squids. Most shallow-water squids leave clumps of eggs attached to the seafloor or release neutrally buoyant egg masses containing thousands of eggs that drift in the water column. Deep-dwelling armhook squids have a different strategy. With the seafloor far below and predators plentiful, female armhook squids cradle their eggs in their arms. 

While brooding, a mother squid will not eat. Instead, she survives on fatty lipids stored in her digestive gland, an organ analogous to the liver in humans. She retreats to deeper waters of the midnight zone, beyond the reach of air-breathing predators like beaked whales and elephant seals and too far above the seafloor for bottom-dwelling fishes and sharks. In about nine months, her eggs will hatch, and then she will die. Her sacrifice gives her offspring a better chance of survival.

Deep-sea squids play a vital role in ocean food webs, eaten by large fishes, sharks, whales, dolphins, seals, and seabirds. They make up a large part of the diets of commercially important fishes like tunas, swordfish, and billfishes. Despite their ecological and economic importance, we still know very little about the lives of deep-sea squids. MBARI’s work is answering fundamental questions about the biology of deep-sea cephalopods and providing vital information that resource managers can use to inform decision-making about the ocean.