The world’s attention may be turning its focus to human athletes at the Olympics in Paris, but elephant seal observers are celebrating our own local seal athletes.
A new exhibit at the Friends of the Elephant Seal Visitor Center in San Simeon puts three seals on the metaphorical platform, for migrations of more than 6,000 miles over seven months.
The exhibit characterizes them as three human swim champions: Diana after Diana Nyad, Katie after Katie Ledecky, and Trudy after Gertrude Ederle.
Diana Nyad is a long-distance open water swimmer who swam from Cuba to Florida in 2013, through stinging jellyfish and sharks. Katie Ledecky is a competitive swimmer who has won seven Olympic gold medals (2012, 2016, and 2020) and 21 world championships. Gertrude Ederle was the first woman to swim the English Channel in 1926.
Two annual migrations
Female elephant seals have the advantage over human swimmers, spending 10 months of the year in the ocean.
They swim two annual migrations, a short one and a long one.
The short migration, about 10 weeks, comes after they wean their pups in the early spring. Elephant seal mothers don’t eat while they are nursing their pups, so they lose about a third of their body weight. It’s physiologically draining.
By the time the pup is big enough to wean, the mother is thin. She needs to regain blubber.
So she leaves the beach in February or March, returning in April or May. At that time, she stays on the beach for four or five weeks to molt her skin.
When she returns to the ocean, it’s for her long migration, seven to eight months. The next time she comes out of the water, it will be to have her pup in January.
What are they doing out there?
All elephant seal females spend those months feeding in the open waters of the North Pacific.
But some go far west, 3,200 miles, to feed.
Roxanne Beltran’s research team at University of California Santa Cruz documented the long migrations by tagging female seals. The one nicknamed Diana was tagged twice and made the same journey twice.
Female elephant seals have to eat almost constantly to gain weight and support the developing pup. Most forage on small fish in the mesopelagic layer, although about 15% dive down to forage on the ocean floor along the continental shelf or at seamounts.
They have to gain enough weight to support them in their travels, and to develop a pup and then carry them through nursing the pup for a month. That’s a lot of blubber.
They share the mesopelagic layer with a few other large species: sperm whales, beaked whales, blue sharks and salmon sharks. Scientists don’t know much about how they all share this ocean resource.
Season statistics
The exhibit gives these athletes’ stats on their migrations: how far they went, how long they were at sea, how much weight they gained.
With one exception, they each did it while pregnant, having a pup every year.
Trudy and Diana spent 223 days at sea. Katie made her trip, to a point 3,436 miles west, and back in only 185 days.
Diana gained the most weight, 448 pounds, while Katie gained 279 pounds and Trudy gained 293 pounds.
What’s out there?
They all went to the same general location but probably didn’t interact with each other. Seals are solitary.
“Although there are a lot of elephant seals, maybe 240,000 total, they are foraging in a HUGE volume of the ocean,” Beltran wrote in an email. “so they likely don’t encounter each other often.”
Perfect timing
The tricky part is heading back to the beach in time to give birth to the pup. They have to find their way around the open ocean, catch and eat enough fish to gain weight and support the developing pup, and then turn around and find their way to the beach to have that pup. They give birth within five days of returning to the beach.
Beltran’s research team found that the seals have a “map sense” that allows them to know how far they are from that home beach, and how to manage their time, at about 100 miles a day, to get back.
“We found that the seals’ abilities to adjust the timing of their return migration is based on the perception of space and time, which further elucidates the mechanisms behind their astonishing navigational feats,” the academic paper’s summary states.
No one yet knows how they do it. Geomagnetic, celestial, acoustic or olfactory senses may be involved.
For now, observers use electronic tagging to learn what the seals are doing and welcome them back to the beach when they arrive in January, in time to have their pups.
August seal viewing
The bulls, fully mature ones and younger ones, are now on the beach at Piedras Blancas. They are molting their skin, the annual shedding. Docents have samples of shed skin for visitors to handle.
Bulls are generally quiet at this time. With no females to fight over, they spend their days resting on the sand.
Christine Heinrichs’ elephant seal columns were recognized by the National Society of Newspaper Columnists with a first-place award in the General Print category of the 2023 annual contest.
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