Marine scientists solve mystery behind decapitations of seal pups on California coast
Coyotes are the likely culprits behind the gory decapitations of baby seals in Northern California, researchers said.
“I think it’s an exciting thing. It’s a predator-prey relationship that’s developing. It’s nature happening,” Sarah Codde, a marine ecologist with the National Park Service at Point Reyes National Seashore, of the discovery.
Since at least 2015, headless seal pup carcasses had turned up on Northern California beaches, Sarah Grimes, a marine mammal stranding coordinator with the Noyo Center for Marine Life, .
The attacks were mainly concentrated on harbor seals at MacKerricher State Park in Mendocino County, Grimes said.
“I was like marine mammal CSI, seeing all the dead pups with their heads torn off, and I’m like, ‘What the heck did that?’” Grimes added of the years-long mystery.
By 2020, the then-unidentified predators were also taking chunks of the flippers of 300-pound weaned elephant seal pups at Point Reyes National Seashore, according to the Mercury News.
Experts were initially baffled by the grisly finds — and wondered if it could possibly be the work of humans or even a skin disease among the seals, Codde explained.
The problem seemed to dissipate in 2020 and 2021, but weaned pups with flipper bites turned up again this year, Codde told the outlet.
Eventually, Codde enlisted the help of Frankie Gerraty, a doctoral student at the University of California, Santa Cruz, who set up a camera at Point Reyes and caught the attackers in the act.
“The coyote was really struggling to pull at it, and the seal was trying to pull away. We caught it for about six minutes of the coyote pulling and biting, and then the seal would get away, and the coyote would get it again, and then they went off-screen,” Codde said of the footage.
In the fall, Gerraty also set up a camera at MacKerricher, where they captured footage of a coyote attacking a harbor seal and “beheading it,” he explained.
“Coyotes are underappreciated predators in shoreline ecosystems, and marine mammals are the largest and most calorically rich nutrient parcels in the ocean, and really anywhere in the world,” Gerraty added.
The teams still do not know why the coyotes only eat the pups’ heads — or why they only attack the elephant seals’ flippers.
“For all the pups we saw with injured flippers, there were no other bites anywhere else on the body. We didn’t know why they would do that, what was the purpose, what is the nutritional value,” Codde explained.
“Maybe they think it’s a carcass, and then they go there, and they take a bite, realize and run away,” Tali Caspi, a doctoral student at University of California, Davis, who studies coyotes, told the Mercury News.
Seals and sea lions may have become more comfortable having pups on beaches — rather than on sandbars — since land-bound predators have mostly been chased away by ranchers, the outlet noted.
But now coyotes are encroaching closer to the water.
“Everyone was fat and happy, and no one was disturbing them. Then populations of large predators started to rise, and suddenly, now, there’s a killer in the mix,” Grimes said.
Researchers are already seeing fewer harbor seal pups at MacKerricher Park, she added.
“Harbor seals are pretty skittish. Maybe the smarter ones are realizing they failed to pup for the past few years, and they are choosing a different site,” she speculated.
The harbor seal count at Point Reyes might also be waning.
“There is definitely more research that needs to be done on a statewide population look of harbor seals so that we can see if they are moving to different areas,” Codde confirmed.
“If harbor seals have to find new locations because of coyotes, we have to be mindful of that and protect those areas from human disturbance,” she added.
