Elephant seals versus white sharks at Isla Guadalupe

“Nunca lo habían hecho antes” (translation: it has never been done before)! This became our motto on our recent research trip to Isla Guadalupe, Mexico where we are studying the predator and prey interactions between northern elephant seals and great white sharks. The phrase was inspired by a documentary about the island, and it is really fun to say in a booming and dramatic voice (try it!).

Isla Guadalupe, our field site, is a small volcanic island ~250 kilometers (or 150 miles) off the coast of Baja California, Mexico. Isla Guadalupe is a dream-come-true for marine biologists! It is home to many different species of large marine animals, including Laysan albatross, dolphins, northern elephant seals, Guadalupe fur seals, California sea lions, and white sharks. Of all these species, the white sharks are probably the most famous, as Isla Guadalupe is one of the best places in the world to see white sharks and people pay a lot of money each year to cage dive with the sharks off the coast of the island.

Large marine vertebrates (Laysan albatross, Guadalupe fur seal, and unknown dolphin species) at Isla Guadalupe (photo credit: Sarah Kienle and Stella Villegas-Amtmann)

The goal of our research on the island is to understand the predator and prey interactions between northern elephant seals and white sharks (“nunca lo habían hecho antes”; it has never been done before). One of the reasons white sharks are so abundant around Isla Guadalupe is because of the smorgasbord of pinnipeds (seals and sea lions) that call the island home. White sharks are one of the only known predators (along with killer whales) of elephant seals. Recently, researchers have noticed that more and more elephant seals have bite marks from white shark attacks. The seals with these scars are the lucky ones—they survived the attack. Many others are likely not so fortunate.

The most dangerous time for an elephant seal on Isla Guadalupe is when they arrive to the island and when they leave the island. Elephant seals come to land twice a year: (1) during the breeding season (December to February) where seals give birth, nurse pups, and mate, and (2) during the annual molt (April to June) where seals lose and regrow all their hair and skin. The rest of the year the seals are at sea feeding throughout the North Pacific Ocean.

In May 2017 we deployed six sets of instruments on female elephant seals. These instruments give us a ton of information about the seal’s positions on land and at sea, their diving behavior, and their potential proximity to white sharks when they arrive and leave Isla Guadalupe. An adult female seal weighs ~400 to 600 kilograms (900 to 1,300 pounds) and measures 2.5 – 3.5 meters (8 to 12 feet), so as you might imagine, working with elephant seals safely is not an easy task. We sedate the animals to safely work with them, and then we attach the instruments to their fur with epoxy. We also take a variety of measurements (mass, length, girths) and tissue samples from each female and her pup that give us a wealth of information about the seal’s health and diet. Over the last several years our collaborator, Dr. Mauricio Hoyos, has deployed similar tags on the white sharks and has identified the majority of the individuals around Isla Guadalupe.

Northern elephant seals at Isla Guadalupe with satellite tags (top left), white shark bite scar on neck (top left), and at the Punta Norte colony (bottom) (photo credit: Sarah Kienle and Stella Villegas-Amtmann)

For the last eight months, the six female elephant seals have been feeding throughout the North Pacific Ocean, and they returned to Isla Guadalupe at the end of December for the breeding season. A multinational team of researchers from three organizations with an absurd number of acronyms (UCSC, CIAD, and CONANP) converged on Isla Guadalupe two weeks ago to find the tagged seals, get the data from the instruments, and re-deploy the tags on new seals. We were moderately successful.

The first two days were exciting! We successfully recovered the instruments from three of our seals. One of those seals was an animal that had stopped transmitting her positions a few days ago, so we were excited to find out she was alive and hadn’t been eaten by a white shark. While we were on the boat on our way back to the fisherman’s village for the night, we even spotted a fourth animal on a different beach called Playa Elefante (named for the abundance of elephant seals on this beach). We made all sorts of plans to go and get her the following day.

Our research team

Unfortunately, when you are working on an island in the middle of the ocean, everything is dependent on the weather gods, and they were not feeling generous. All of our field sites were only accessible by boat. Not a single boat left the fisherman’s camp for the next five days, so we were stuck in the village. Additionally, we were never able to find another seal that had stopped transmitting her positions at sea. And, perhaps most frustrating of all, one of the seals who had arrived on the island three days prior to our trip, left the island the day we flew in. We have never seen this behavior in an elephant seal before during peak breeding season (nunca lo habíamos visto antes). Despite the frustrating wait for the weather to improve, knowing we had one hope to get back out to Playa Elefante (spoiler alert: we didn’t), things weren’t all bad. We feasted on lobster, abalone, fresh caught fish, fried chicken, frijoles, hand made flour tortillas, and chocolate abuelita. We also had a movie afternoon watching Jacque Cousteau and his team studying elephant seals in unorthodox ways at Isla Guadalupe ~50 years ago. We also got our first look at the dive data from the three instruments. Much to our excitement (there may have been some yelling involved), we saw that the elephant seals at Isla Guadalupe behave different—their dives to and from the island are long and deep, and this is likely to avoid being attacked by white sharks.

The weather never improved and with more storms rolling in, there was no chance we could get to Playa Elefante to recover our last tagged female. Luckily for us there were nine females on a beach within walking distance of the fisherman’s camp. This group was perfect to work with because there were only two small males to keep an eye on and lots of sleepy animals at low tide in the afternoon sun. We deployed two sets of instruments successfully on healthy females with super fat pups. And, with that, we were done! We finished in perfect time to watch our last sunset on Isla Guadalupe.

Now, we wait for the females to update us on their movements and dive behavior. We hope that none of them get eaten by white sharks. And, our fingers are crossed that they continue to do things that nunca lo habían hecho antes (it has never been done before)!

Final day at Isla Guadalupe (photo credit: Sarah Kienle and Stella Villegas-Amtmann)

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