Although California’s sea otter population continues to stabilize, sharks are still taking a toll on the furry marine mammals living on the Central Coast.
The U.S. Geological Survey on Friday released the results of its annual southern sea otter survey, which reported the three-year average at 3,186 animals, according to a USGS report.
Otters were counted in three regions, from Pigeon Point north of Santa Cruz down to Gaviota State Park in Santa Barbara County. The survey also included San Nicolas Island, part of the Channel Islands off the coast of Ventura County.
California’s once prosperous sea otter population was decimated by the fur trade in the early 1800s. For nearly a century, the animal was believed to have been hunted to extinction in California until a small surviving colony was discovered in central Big Sur in the 1930s. Since then, the otters have returned to the coast, although they’re still listed as a federally threatened species.
This year’s count is down 3 percent from 2016, when the three-year average was 3,272 otters, according to the release.
Even so, the count exceeded 3,090, the number needed to remove the otters’ threatened designation. The population must exceed that number for another year before it will be taken off the list.
The otter population in the central region — starting at Seaside, near Monterey, and ending in Cayucos — has increased, according to a USGS chart. The number of otters in the north, from Pigeon Point to Seaside, has declined.
The number of otters in the south region — which stretches from Cayucos down to Gaviota and encompasses most of San Luis Obispo County — has also gone down.
The otter decline in those areas is due to an increase in shark bite-related deaths, according to Tim Tinker, a USGS research ecologist. Tinker said the population now is the lowest seen since 2002 and 2003.
The shark population in Southern California has grown since tighter fishing regulations were put in place, causing them to travel north to feed on sea lions and elephant seals, Tinker said. Sharks don’t eat otters but may bite them when hunting because they resemble juvenile versions of their prey.
A study Tinker helped write for Marine Mammal Science in 2015 said more than 50 percent of sea otter carcasses found along the California coast were killed by sharks.
“Sea otters in this one area are collateral damage,” Tinker said.
The burgeoning shark population is healthy, but otters haven’t increased the range of their colonies up and down the coast, he said: “Hopefully, over time, that will happen.”
In spite of the sharks, there are still more otters in Morro Bay now than there were in the early 2000s, according to a May survey the state Department of Fish and Wildlife conducted. Researchers counted 36 otters this year, up from the five or fewer seen in the past.
Last week, a Morro Bay otter that spent months rehabilitating in Marin County from domoic acid poisoning was released back into the harbor.