An unexpected culprit is decapitating baby seals in California

Earlier this spring, researchers discovered a grisly scene in the sand at MacKerricher State Park near Fort Bragg in Northern California. 

Ice plants spattered with blood indicated there had been some kind of a scuffle just a few feet away from the crashing waves. Though paw prints still covered the beach, the unknown predator was long gone. What remained was the carcass of a harbor seal pup, its head completely gnawed off. 

“It’s somewhat gruesome,” said Frankie Gerraty, a Ph.D. student at the University of California, Santa Cruz who has been studying the phenomenon with cameras set up along the California coastline. “We realized there are a handful of sites where harbor seal pups are dying at unusually high rates with distinct patterns of mortality. And for a while, it was really a mystery as to what was going on.” 

Sightings like this have been occurring as far back as 2015, according to Sarah Grimes, stranding coordinator for the Noyo Center for Marine Science in Mendocino County, who said she’s recorded a dozen or more dead, headless seals per year at MacKerricher State Park alone.

“I love these animals, so it was a gut punch when I started to see these helpless little ones torn apart,” she said. “Putting on the scientific hat made it easier to do the detective work — taking measurements, looking at tooth marks — so we could try to get to the bottom of this.” 

But it wasn’t until recently that Gerraty captured the culprit red-handed, as the Mercury News first reported. 

On April 23 at 11 p.m., one of his motion-sensor cameras was triggered at MacKerricher State Park and recorded about five minutes of footage. Gerraty, who had been staying at a campground nearby, took out the camera’s SD card the following morning, plugged it into his laptop and began to scroll through the shots, anticipating a lot of blank images.  

“When I opened my computer, I was pretty shocked to see it,” he told SFGATE. “We had a few minutes of this coyote dragging a seal into the frame and munching off its head before dashing off-screen.” 

Now, researchers are attempting to determine the extent of the coyotes’ hunting behavior, why it seems to be a trend in certain locations in California, and whether there are consequences for the species involved. Gerraty is doubtful that the predation alone would cause harbor seals’ strong population numbers to decrease, but it may lead to shifts in where the seals choose to haul out and give birth. It’s possible they could leave their usual rookeries for sites that are more or less suitable for their pups, he said. 

And because seals’ tissue can be loaded with contaminants often found in the marine food web, such as mercury, it’s possible those could become transferred to land-dwelling animals as a result of the coyotes’ consumption habits, he continued. 

More information isn’t yet available because the researchers are hoping to collect more data from camera traps again in the spring, and the full study isn’t expected to be published until the end of 2024 or early 2025. But the knowledge they have so far is eye-opening. 

“Oftentimes, people would be like, this is terrible,” Gerraty said. “Coyotes have emerged as a villain in people’s minds in terms of how they relate to them. They’re thought of as pests. But they’re both native predators on land and in the ocean. This is nature in action. This is probably a relationship between marine mammals and terrestrial animals that existed historically but was severed, and this could be a restoration of this relationship.”

Sarah Codde, a marine mammal ecologist for Point Reyes National Seashore, said that in 2020, she also observed coyotes attacking weaned elephant seal pups near South Beach. About 30 of the pups’ rear flippers were bitten, but all of them survived, and otherwise appeared to be healthy. The behavior wasn’t observed in 2021 or 2022, but this year, four more weaned elephant seal pups with gnashed flippers were recorded on Drakes and South beaches. These pups also survived, but appeared to be malnourished and weak. 

“We don’t know if this is a new behavior that will continue or if it was just an abnormal event,” Codde said, noting she’s only seen about four or five events of coyote predation on harbor seal pups in the area. “We checked with other elephant seal researchers in California, and no one has seen this before.”

However, coyotes have been documented hunting harbor seals elsewhere along the West Coast, specifically in Washington and Canada, for several decades, said Christine Wilkinson, a conservation biologist and carnivore ecologist at the University of California, Berkeley and the California Academy of Sciences.

The phenomenon may have begun after coyote populations bounced back from near extirpation due to overhunting around 1900, she said, and they expanded their range to new habitats all over the U.S. Wilkinson suspects their tendency to prey on seals could be a result of this historical shift and expansion in their range, which was made possible after extirpation of other apex predator populations like the grizzly bear, which was wiped out in California by the 1920s. Coyotes no longer had to worry about fellow carnivores that they otherwise could have been hunted by and would have had to tiptoe around, she said. 

But there’s only so much documentation available surrounding these patterns and when they started to develop, Wilkinson noted, in part because of the public perception of coyotes.

“​​To be honest with you, people vilify and disregard coyotes a lot,” she said. “It’s changing slowly, but there’s a lot of galvanizing around studying them, especially urban coyotes. My speculation is that maybe this behavior isn’t super new in California — people just haven’t been looking for it.” 

Meanwhile, the passing of the Marine Mammal Protection Act in 1972, which made it illegal to harass, hunt, capture, collect or kill marine mammals, likely played a role in the seals’ own population rebound, said Rachel Reid, a paleoecologist and research scientist currently based at Virginia Tech. Reid previously studied changes in coastal coyote diets at UC Santa Cruz, and in her research, she found that seals made up about 20% of coyote diets at Año Nuevo State Park. She also learned that historically marine mammals were not an important part of the carnivores’ sustenance. Reid and Wilkinson agree that these changes in the coastal environment could be making the coyotes’ behavior more prevalent. 

“I think it’s really interesting,” Reid said. “Coyotes have been on the coast of California for thousands of years; people find coyote bones in the La Brea tar pits. It’s not a new place for them, but maybe they’re spending more time there than they did previously because they don’t have as many competitors. There’s an opportunity for coyotes to gain access to a resource they may have had to compete more heavily for.”

There’s also the reality that seals are not as graceful on land as coyotes are. While the canines have been spotted wandering through elephant seal colonies and scavenging for dead pups, much to the indifference of the adults, Codde said, hunting down the live ones could simply be a matter of convenience. 

“Beaches are sometimes carpeted with these animals,” Wilkinson said. “If the seals are readily available, and so easy to capture, why would they pass up this massive, accessible food source and go through the work of hunting for something else?” 

Why coyotes are biting off the harbor seals’ heads, however, is still a big unknown. Gerraty hypothesized that the predators just may not have enough time to eat the rest of the body before birds and other scavengers get to it. What’s likely, he said, is that the seals’ brains are particularly rich in nutrients, and that canines, not just coyotes, are instinctively inclined to go for them. For instance, he said, hyenas have been observed exhibiting similar behavior when hunting for seals along the Skeleton Coast in Namibia.

“I also imagine it’s a lot harder to get through the blubber of a living animal and get the most bang for your buck,” Wilkinson said. “From a coyote’s perspective, it could be a better payoff to go for the flippers or the head.” 

As Gerraty’s research expands, and more wildlife organizations are getting involved on a statewide level, he hopes people are able to gain a better understanding of each species and the respective roles they play in the ecosystem. 

“While obviously it is traumatic to have seal pups dying, coyotes are also amazing, adaptable animals,” Gerraty said. “They’re really able to identify and exploit new food resources. I think both species are equally valuable as important predators that share landscapes with us. And the fact they share this relationship that perhaps we never noticed before is captivating.”