Federal and state officials are investigating the shooting deaths of California sea otters, after the bodies of four male otters were found washed up on beaches near Santa Cruz.

On Monday, the US Fish and Wildlife Service announced a $10,000 reward for information that leads to the arrest and conviction of the person responsible for killing three sea otters that were found between 12-19 August.

A fourth otter carcass was discovered on 20 August with a suspected gunshot wound, Ashley Spratt of the Fish and Wildlife Service said on Wednesday.

“Finding several gunshot sea otters at the same general location during such a short time frame is very unusual,” said Spratt.

“We don’t know why these otters were shot, but what’s important to note is that killing or harassing federally protected wildlife is a crime.”

Sea otters are protected by the Marine Mammal Protection Act, California state law and the Endangered Species Act. Killing a sea otter is punishable by fines up to $100,000 and could result in a jail sentence.

Sea otters were once widespread along the Pacific coast, but the mammals were hunted almost to extinction for their pelts during the 18th and 19th centuries.

In 1977, California’s remaining sea otters were listed as “threatened” under the Endangered Species Act.

“They’re a keystone species. They help play a role in the broader ecosystem,” said Spratt. “So with the loss of these sea otters, we also have the loss of their benefit to the ecosystem.”

Today sea otters are primarily threatened by oil spills and coastal tanker traffic, Spratt said, although otter killings by humans are not unheard of.

In September 2013, three dead otters were found near Asilomar state beach, an unsolved crime that Spratt said is now considered a “cold case”.

The otter carcasses have been transported to the US Fish and Wildlife forensic lab in Oregon, where they are undergoing necropsies.

