Millions of krill, a tiny shrimp-like animal that is a cornerstone of the marine food chain, perished last month along a 250-mile stretch of beaches from Oregon to northern Humboldt County.
Scientists are still investigating the massive krill stranding in mid-June, but their working hypothesis is that a shift in the wind caught the animals near the ocean surface, possibly in a mating swarm, causing them to be swept ashore.
"Once they get into the surf line they are in trouble," said Joe Tyburczy, a scientist with the California Sea Grant Extension in Eureka who is a coordinator of the investigation.
The strandings were reported from Newport, Ore. to McKinleyville in northern Humboldt County on June 16-18, making it the geographically largest krill die-off on record, Tyburczy said.
On a beach just north of the mouth of Redwood Creek in Redwood National Park, dead and live krill formed a mile-long pink band on the sand just above the high tide line on June 17, according to David Anderson, fishery biologist at Redwood National and State Parks.
A much more limited stranding of the less than inch-long crustaceans at Bodega Bay was documented by a Bodega Marine Laboratory worker on June 21, but experts said they are not sure whether the events are related.
Jackie Sones, the marine lab's research coordinator, said she noticed a flock of gulls on the beach at Horseshoe Cove, a place the birds seldom visit.
Sones photographed the krill, which the gulls were eating, on the beach and under a lab microscope, and said she hasn't found any since that day.
"I am keeping my eyes open," she said.
John Largier, an oceanographer at the marine lab, said an unusually strong vortex, a swirling ocean current, occurred off the Sonoma Coast in mid-June. The current might have swept krill away from land and minimized the die-off here, he suggested.