BioEd Online

What do you do if you find yourself with a couple of thousand eggs? If you're the squid Gonatus onyx, the answer is simple: take them for a swim. The creature is the first squid ever discovered carrying its huge brood around under its arms.

Squid usually lay eggs on the sea floor and leave them to develop and hatch unattended, says Brad Seibel of the University of Rhode Island in Kingston, who captured pictures and videos of squid behaviour while working with colleagues at the Monterey Bay Aquarium Research Institute in Moss Landing, California.

But G. onyx, one of the most abundant squid species in the Pacific and Atlantic oceans, is different. Researchers had suspected that it carries its brood around, but until now had been unable to confirm this because the creature often dives to depths of more than 2,000 metres.

Seibel and his team used a remote-controlled submarine to observe five squid, each carrying 2,000-3,000 eggs. They report the discovery in Nature¹.

"It's truly amazing to watch," says Seibel. "I was surprised by many details of the process, such as the agility of the squid despite carrying a large mass of eggs."

Carrying a large egg mass is still a burden, potentially placing broody mothers in greater danger of being eaten by whales or elephant seals. But the benefits of ensuring that more eggs survive and hatch may outweigh this risk, Seibel says.

"These squid reduce predation risk by diving deep in the ocean," he explains, "and then spend lots of energy ensuring that the eggs hatch at a large, capable size."