The 160kg animal swam and waddled its way to the ranch in Washington state but has failed to survive the sea, biologists say

This article is more than 4 years old

This article is more than 4 years old

A sea lion that baffled scientists after being found in the driveway of a cattle ranch about 80km (50 miles) from the ocean in Washington state has been found dead two weeks after being released into the sea.

The male California sea lion was released into Puget Sound on 15 April after it apparently swam and waddled its way to the ranch near Oakville, the Tacoma News Tribune reported.

But it has been found dead under a bridge in Olympia and biologists are now investigating the unusual case.

Dyanna Lambourn, a Washington state fish and wildlife biologist, examined the sea lion and found no immediate cause of death. Samples from the necropsy were sent this week to test for possible causes.

The animal’s wayward journey to Soggy Bottom Farm began some time before 15 April.

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Ken Shively, a rancher, found the large animal in his driveway and initially thought it was a deer or elk. The sea lion was about 200m from a tributary of the Chehalis river, and roughly 80km of river, creek and drainage ditch travel from Washington’s coast.

He called state wildlife officials. “They didn’t believe us,” Shively told the News Tribune. “They were like, ‘A what? Can you describe that to us?’”

Bob Weaver, a sergeant with the agency’s enforcement division, said it was the most unusual call he had received in years.

“I’ve dealt with sea lions before, but never in a cattle farm,” he said, estimating that the animal travelled about 8km (five miles) up a shallow creek.

Sea lion are known to travel long distances up rivers in the pursuit of salmon and other fish. “The unusual part is that it went up that little creek,” said Steve Jeffries, a research scientist with the state wildlife department.

Agency staff corralled the sea lion into a cage on a flatbed trailer, and released it that evening into Puget Sound near DuPont.

Lambourn, who examined the sea lion at the ranch, found no obvious injuries or illnesses. However, its weight of 160kg (350lb) was half the normal level for an adult male sea lion.

Biologists are investigating whether the animal could have ingested domoic acid, a neurotoxin produced by algae blooms, on its journey inland. Domoic acid can affect a sea lion’s neurological functioning and cause seizures.

In California, where all sea lions originate, the population has been hit by low birth rates and high mortality. But Lambourn say the overall population of about 300,000 animals is in good shape.