Scientists on Tuesday conducted a necropsy — an animal autopsy — on a 10-foot shark that washed up on San Onofre State Beach just south of San Clemente, to find out just why the sevengill ended up on dry land.
The shark was spotted circling around in shallow water, not far from where surfers were taking waves at the popular “Old Man’s” surf break, before coming to shore on the cobblestone-dotted beach.
A beachgoer tried twice to return the shark to the sea, but it kept coming back to land, said State Parks Peace Officer Lifeguard Todd Shanklin.
“They can be aggressive if provoked, so I didn’t want anyone pushing it back in the water,” he said Monday, Dec. 16. “We’re kind of taking a wait-and-see approach and letting nature take its course.”
Retired ranger Jim Serpa rushed down to see the shark. In his decades overseeing south county beaches, he said, he had never seen the species in local waters. “It’s pretty trippy looking, isn’t it?” Serpa said.
Serpa, who gives educational talks on sharks, said they typically have five gills and that it’s a more primitive species that has seven.
“This is a really old type of shark,” he said before measuring its length and inspecting the body to determine it was a female.
Chris Lowe, director of the Shark Lab at Cal State Long Beach, said the shark species migrates regularly, swimming from Washington state to Southern California and Baja before turning back around.
“They were fished pretty heavy in the ’60s and ’70s, and populations have been coming back,” Lowe said.
They hunt in groups, like wolves, he said. They typically feed on crabs and crustaceans in kelp beds, but will gang up on bigger pray, such as seals.
“The only way they can take down a seal is to work as a team,” Lowe said.
The cause of death could range from a hook lodged in the shark’s gut, to a bacterial infection that eats at the brain.
Being able to study the shark allows researchers a glimpse into the complex sea creature.
“Most of the time when sharks are sick, we never see them. They sink to the bottom and die,” Lowe said.
One theory was that it was a brain-eating bacteria, similar to what happened to a thresher shark in Long Beach in June. The “carnobacteria” is common in sea water and is only found in certain fish.
“There are certain strains known to be pathogenic — it gets into the head and starts eating the brain,” Lowe said.
The bacteria used to be found only in small salmon sharks, but more recently there has been evidence of the bacteria affecting other species, including makos, white sharks and threshers.
But as Dr. Mark Okihero, a pathologist with the California Department of Fish and Game, cut open the shark’s head, Tuesday, other theories surfaced, including septic shock — possibly from bites while mating — that introduced infection to the body, said Serpa, who watched Okihero and others study the carcass.
It also might have eaten a ray or rockfish that stung its esophagus and caused the infection, he said.
A final determination on the cause of death, based on the necropsy, is pending.