Cambrian: Opinion

Video illuminates seals’ eating habits down deep

Two young seals tussle in the surf. Serious fighting is reserved for adults in the coming breeding season.
Two young seals tussle in the surf. Serious fighting is reserved for adults in the coming breeding season. Special to The Cambrian

Subadult male seals are arriving in greater numbers on the beach. Lots of juveniles are still sleeping there, but some large individuals have shown up. November is the last month of the fall haul out, when young seals come to Piedras Blancas to rest for four to six weeks.

The large male seals aren’t fully adult, with the trunk-like nose and thick, calloused chest shield. That’s the best way to tell that they are still, at 3,000 to 4,000 pounds, youngsters.

The smallest seals on the beach are the pups that were born last winter. Those that return from their first migration are called the Young of the Year. About half survive that first swim north, learning to hunt along the way.

Diving in deep

Elephant seals hunt at 1,000 feet and deeper. Digital tracking devices make it possible for us to know this, but much of their feeding behavior remains unknown. It’s too dark down that far for a critter cam to function. One seal was tracked over 17 hours of her day. Most of her dives were 20 to 30 minutes long, down to between 1,500 and 2,500 feet. One dive of over an hour brought her to around 4,000 feet.

Knowing where they go lets us infer that they are eating the fish and squid that live there. One remarkable video did catch a female elephant seal eating a hagfish. It was part of a study by Ocean Networks Canada, which placed a pod at about 3,000 feet deep. The lights and camera went on to record video for 15 minutes in every two-hour period.

Hagfish feast

It recorded a huge amount of video, so the word went out to citizen scientists worldwide to watch the video and report interesting events recorded. A dedicated 14-year-old boy in the Ukraine watched long enough to see a female elephant seal slurp up a hagfish!

Hagfish are living fossils, unchanged more than 300 million years. They are primitive fish, with no jaw. Instead, their teeth flex out from inside their lips. They travel in schools, feeding on the ocean bottom, eating worms and carcasses of dead animals that float down.

Eating a hagfish is more difficult than she makes it look. When they are threatened, hagfish nearly instantaneously cover themselves with sticky, gooey slime. (Do the Ghostbusters know about this?) It’s so thick and viscous that sharks have to spit them out. The slime clogs their mouths, making it impossible for them to breathe in water. Elephant seals, even if they took longer to eat a hagfish and it bloomed its slime protection, could eat them anyway. They breathe at the surface, so no problem for them.

Improvements in digital technology will undoubtedly advance so that we can know more about what and how elephant seals eat. For now, we can be confident that those huge seals resting on the beach represent lots of food consumed.

Adult males will arrive in December, preparing for the breeding season to come in January.

Christine Heinrichs is a longtime elephant seal docent. Her monthly column is special to The Cambrian.