Why 'Chonkers' the Steller sea lion is such a rare sight

A massive sea lion nicknamed “Chonkers” is having his moment at Pier 39 in San Francisco, drawing crowds eager to take in his sheer size.

“I usually come into work around 7:30 a.m. and he's already up and out there on the floating dock,” says Stephen Arsenault, marina maintenance assistant at Pier 39. “Typically he'll hang out until about 10 o'clock and then jump in the water and spend the rest of his day in the bay.”

Sprawled across the dock, he might appear like any other sunbathing sea lion. But that bulk tells a different story. This is an animal built for the open ocean, made for cold water, defending territory and a life far beyond the harbor.

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Chonkers is not a California sea lion, the species people are used to seeing along the coast. Instead, he’s a Steller sea lion, a species that ranges along the North Pacific Rim, from northern Japan through Russia and Alaska and south to central California.

While the two look similar, there are key differences—most notably size, with Steller sea lions growing over twice the size of California sea lions.

“It is quite obvious if you've seen the pictures that one of these things is not like the other when he showed up,” says Adam Ratner, director of conservation engagement at the Marine Mammal Center in California.

Why Steller sea lions are so enormous

As the largest species of eared seals, male Steller sea lions can reach 11 to 12 feet and weigh up to 2,500 pounds. Once fully mature, they also sport a mane of fur around their necks, like a lion. Females are much smaller, growing to about nine feet and around a thousand pounds. They are light tan to reddish-brown, with a blunt face and a broad, bear-like head.

Stellers need that size for a reason. Living in cold ocean waters, these sea lions rely on thick layers of blubber to stay warm. Their large bodies also help them dive deep—more than a thousand feet—to hunt fish and squid at night.

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For males, size is especially important during breeding season, when they compete to defend territory to mate with females. They often forgo hunting during this time so they rely on the energy stored in their bodies as they may go weeks without eating.

Because of their size, Steller sea lions tend to dominate when they mix with smaller species like California sea lions, says Sharon Melin, a biologist with NOAA Fisheries. That’s likely why the California sea lions slip off the dock when he hauls out.

A day in the life of Chonkers

Why is Chonkers at the pier? Probably the same reason people come here, Ratner says: food. “It’s a good place to rest and hang out, and there’s lots of food around,” he says. “That’s really what makes Pier 39 special—it’s a protected area, away from predators, he added, as white sharks and orcas don’t really come into the bay.

“Chonkers is clearly not one missing out on the food right now and probably thoroughly enjoying the buffet of anchovies and other foods that's at his disposal,” Ratner says.

Like other sea lions, Steller sea lions rely on land to rest, molt, and socialize, gathering in large numbers at breeding sites known as rookeries. In California, small rookeries exist on offshore islands including the Farallones and Año Nuevo.

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Outside the breeding season, they spread out more—including to places like Pier 39—to find food and rest wherever they can find a good spot.

But this time of year, males like him are in a lower-energy, non-breeding state, with lower testosterone. “They’re in winter mode, just getting fat. They’re not breeding,” Melin says. “So he’s just hanging out—and might be wondering why [the other sea lions] jumped off. They do like to be next to other animals.”  

Soon, Chonkers will likely leave and head to the rookery sites to establish a territory for breeding season, where the odds aren’t quite yet in his favor given that he’s a younger male. “He'll probably try, but he won't be successful. He'll give it a good shot,” Melin says.

Young males often behave this way, learning how to compete and become territorial by spending time around others at the rookery. “The species is just big, but only the biggest and only the strongest get to reproduce,” says Ratner.

In the meantime, if you want to catch a glimpse of Chonkers, check out the live feed of Pier 39.

What makes this sighting unusual

Chonkers is not the first of his kind to appear at Pier 39. Arsenault says there’s usually one that shows up every year or so, and they stay a few days before leaving. Chonkers himself arrived March 13. His lengthy stay is what is more unusual.

And while it’s not totally unexpected that he’s there, it is less common. For instance, at the Marine Mammal Center, they’ve rescued a total of 43 Steller sea lions, out of a total of 27,000 marine mammals in their 50 years, says Ratner. By contrast, they’ve rescued more than 17,000 California sea lions and more than 5,000 northern elephant seals. “It is really, really rare,” he says.

Ratner, Melin and others say that what makes Chonkers and Pier 39 so special is the rare chance to see wild animals up close. “What I love most about the Chonkers story is that it gives us this opportunity to see this amazing wildlife right here, in a major urban area,” Ratner says. “It shows how marine mammals and people can share the same space in a way that benefits both.”

Arsenault says the attention is noticeable. "We're getting a ton more foot traffic,” he says. “I've been asked multiple times like, Hey, where's the Steller sea lion? So that's kind of different."

It’s special to see such a rare animal, especially because Steller sea lions haven’t always thrived in these waters and face ongoing threats.

Steller sea lions were split into two distinct groups in 1997. The western population remains listed under the Endangered Species Act, while the eastern population—like the one Chonkers likely belongs to—was listed as threatened before recovering enough to be delisted in 2013, the result of years of protection and management. For instance, managers created protected buffer zones around rookeries and haul-out sites to keep fishing activity away, helping females and young have better access to food and improving their chances of survival.

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Even though some populations have rebounded, Melin cautions against complacency. Marine heat waves and events like El Niño can still have major impacts, especially on coastal species like Steller sea lions, she says, such as shifting where their prey is found and how abundant it is.

Past heat waves have shown how vulnerable they are, with fewer adult females surviving after the 2014–2017 heat wave. “And you really worry about that, because once you lose your females, the population suffers for a while,” Melin says. Threats to these populations still exist, and we can’t afford to ignore them, she adds. “We do have a responsibility to them—they're just such a treasure.”