From this month's column in The Cambrian:
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.
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 over 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.