Scientists catch culprit behind serial seal decapitations in the act

Decapitated seals have been turning up along North American coastlines for several years. Some experts have suggested humans were to blame for sea lions, harbor seal pups, and various other pinnipeds losing their heads. One private investigator went so far as to suggest the "cuts were surgical."

It turns out that canids, not beachfront butchers, were to blame.

What's the background?

Private investigator David Stuart was among the beachgoers to express concern in 2016 about the discovery of headless seals and ponder their fate. After coming across one such decapitated mammal on Garry Point Park beach in British Columbia, Stuart told Richmond News that the incision was extremely clean, "almost laser precision."

"The seal's rectum has been removed and cauterized; it makes no sense," continued Stuart. "This was a crime scene as far as I was concerned; this needed to be looked at."

Years later, after numerous other incidents were reported on the West Coast, 21 headless seals turned up on the other side of the continent, along the shores of Nova Scotia, Canada. Mammal zoologist Dr. Anna Hall, who noted a similar trend was impacting sea lions in British Columbia, suggested humans might have been responsible, reported the National Post.

"The carcasses have a distinct similarity to them," said Hall. "While we can't say definitely that the seals on the East Coast have been decapitated by human efforts, it does seem that is a distinct possibility looking at the photographs."

Marine mammal biologist Tonya Wimmer alternatively suspected scavengers were to blame, stating, "From the images and information we've received, many of the holes are where the umbilicus would have been and is likely scavenging by other animals."

Caught in the act

Sarah Grimes, a stranding coordinator at the Noyo Center for Marine Science in Mendocino County, California, long speculated about the cause of the headless wonders.

"It was so gruesome," she recently told the Mercury News regarding the headless harbor seals she encountered along the high-tide line in MacKerricher State Park, near Fort Bragg. "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?'"

Frankie Gerraty, a Ph.D. student at UC Santa Cruz, ultimately provided Grimes with an answer, capturing the culprit on tape in MacKerricher.

"We set up camera traps and got one really solid video of a coyote dragging a harbor seal pup and beheading it," said Gerraty. "We are pretty confident there has been predation at four sites along the Northern California coast."

The student noted that contrary to popular wisdom, coyotes — who have made a big comeback from having their numbers suppressed by farmers and ranchers for decades — are often beach dwellers.

"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," said Gerraty.

It's unclear both why coyotes only eat the heads and whether this behavior is altogether new.

Gerraty told the Los Angeles Times, "My guess is that the brains are pretty nutritious compared to a lot of other seal parts. Blubber can be pretty hard to get through."

The student indicated that the coyotes' hunting pattern is unlikely to have a substantial impact on seal populations but may prompt them to relocate where they give birth and "haul out."

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