Elephant Seal, Interrupted

Story by Sara Maxwell and Patrick Robinson, University of California-Santa Cruz

Imagine it. The sun is shining. You’re snoozing on a sandy beach. You’re a Californian – at least for now. You gave birth to a little girl just a few short weeks ago, but already hunger is gnawing at your stomach – it’s almost time to abandon your pup for the cold waters of the North Pacific. Año Nuevo, near Santa Cruz CA, may have good surf, but there’s no food to be found here – at least not for you.

You make a break for the water. You’ve been on land for 35 days without a bite to eat. In fact, you’ve lost more than 200 of your original 900 pounds by nursing your pup…

– she’s grown over 100 pounds – from 40 to 150 pounds – in 28 short days by drinking milk as thick as cream. Now its time for you to eat. You swim for days on end. You dive while you travel – 600 meters deep at a time, coming to the surface only every 20 minute to breathe. You don’t rest. You don’t drink. You don’t sleep – at least not in the way humans know of. Finally, 2600 miles and 35 days later you arrive at the Pratt Seamount Chain in the Gulf of Alaska.

Stretching over 400 miles, it is literally an underwater mountain range, unseen by most human eyes. But you know it is there, and you know there is food. It is covered by deep water corals and sponges, and within their branches and nooks and crannies hides a smorgasbord of food, just like the tropical coral and sponge communities so well known to humans. There is enough food to stay and feast for a month, until you have to make the long journey back to California to do it all over again.

You are a northern elephant seal and you are a survivor. The deep-sea is little known by humans, but you know how to use it to your advantage. Most elephant seals forage in the open ocean, diving sometimes well over a mile to capture the squid and fish that congregate at depths below fronts and eddies. Some head to the continental shelves, foraging along the bottom for the fish that hover near the sediments. But you – you have found something new. Seamounts are your secret – away from the continental shelves and so away from predators, but unlike the moving eddies and fronts, your seamounts are found in the same place time after time – always stationary and always productive.

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Researchers in Daniel Costa’s laboratory at University of California Santa Cruz have been equipping northern elephant seals at Año Nuevo State Park with satellite-linked transmitters, such as the one attached the female elephant seal in the image above, for over 10 years. The Costa lab studies elephant seal physiology, particularly that associated with diving, and how elephant seals can act as indicators of ocean health by understanding how they use the ocean environment through time. Current satellite tagging efforts are part of a larger program called the Tagging of Pacific Pelagics project, tracking over 3000 individual animals from more than 20 taxa, including sea turtles, cetaceans, pinnipeds and fish. You can see the real-time tracks of elephant seals at sea right now at the tracking portion of the TOPP webpage.