Seal Sitters Marine Mammal Stranding Network co-investigator Lynn Shimamoto responds to a dead California sea lion along the West Seattle shoreline.
CNN  — 

Since September, 13 dead California sea lions have washed up in Puget Sound near Seattle, a conservation group says. Eight of the sea lions were shot, and the rest died from other wounds, most likely also caused by humans.

The Seal Sitters Marine Mammal Stranding Network, a volunteer organization that responds to calls for stranded animals, said all the sea lions died from acute trauma – including one found last week that had its head sliced off.

It’s not uncommon for sea lions to get shot – most often by fishermen who believe the animals are reducing salmon populations and harming their livelihood. But the current spate of sea lion shootings is much higher than usual for the months of September through November, the Seal Sitters group says.

And the organization said this is just the beginning. High season for shooting sea lions is typically in the winter months, during fish runs.

Dyanna Lambourn of the Washington Department of Fish and Wildlife Marine Mammal Investigations unit (left) and Casey McLean of SR3 examine the entry wound from a bullet on a dead California sea lion in West Seattle.

“According to those who live and work along the Elliott Bay and Duwamish waterfront, shots are being heard even more frequently this year,” said Robin Lindsey of Seal Sitters in an online post. “Animals searching for food to survive and fishermen searching out fish for consumption or livelihood are on an annual, never-ending collision course.”

Even though California sea lions live mostly in the waters off central Mexico and California, it’s not uncommon to spot them inside Puget Sound. They travel north to feed on the salmon that have returned to spawn.

It’s illegal to kill sea lions

Sea lions are protected under the Marine Mammal Protection Act, and harming one can result in a fine of up to $28,520 and a year in prison.

“We are concerned about a number of recent reports of marine mammal deaths caused by gunshots in the greater Seattle area,” said Greg Busch, an assistant director of the National Oceanic and Atmospheric Administration’s National Marine Fisheries Service’s Office of Law Enforcement. “All marine mammals are protected by the Marine Mammal Protection Act and OLE investigates all reported unlawful takes of sea lions.”

But catching and prosecuting offenders can be difficult. Since 1998 more than 700 California sea lions have been found shot or stabbed in the United States, according to NOAA Fisheries – but only a handful of fishermen were charged.

Seattle’s chapter of the Sea Shepherd Conservation Society, a marine conservation group, is hoping this time will be different. They’re offering a $10,000 reward to anyone with tips that lead to the arrest and conviction of those responsible for the killings and a $2,000 reward to anyone with video evidence.

Field Operations Coordinator Chris Joyce said he’s already looking into some leads and tips that were sent.

“The two suspects are commercial fishermen and tribal fishermen that sell the salmon commercially,” he said. The fishermen are after Chinook, or king salmon, and often blame the sea lions for decreasing the salmon population.

The Washington Department of Fish and Wildlife Marine Mammal Investigations has passed along all the projectiles they’ve recovered from slain seals to NOAA’s Office of Law Enforcement.

Some believe sea lions harm salmon populations

Earlier this year, the US House of Representatives passed an amendment to the Marine Mammal Protection Act that would allow fishery managers and other “eligible entities” with permits to kill up to 100 sea lions each year to help preserve salmon populations.

One of the bill’s co-sponsors was US Rep. Jaime Herrera Beutler of Washington, who has said, “This is a must-pass piece of legislation if we want to save our iconic salmon, steelhead, and sturgeon runs that help make our region so unique.”

The legislation has stalled in the US Senate. But conservationists believe sea lions are under attack.

“The salmon population is in great decline and recreational, commercial and tribal fishermen are looking at sea lions as a scapegoat,” Joyce said.

When fishermen string nets to capture salmon, they create what Joyce described as a “buffet for sea lions.” And when the mammals approach to feed, they sometimes get shot.

What to do if you witness a sea lion shooting

Call the police, Joyce said, if you hear gunshots by a waterway.

“People are witnessing hostile acts by tribal fishermen and those need to be reported,” he said. “Tips are coming in and someone is bound to get caught if they continue killing.”

In the past month, nobody has been criminally charged. But Joyce is hopeful that with the reward, more people will be encouraged to report anyone targeting the animals.

CORRECTION: An earlier version of this story incorrectly cited the organization that has passed along projectiles recovered from the slain seals to NOAA’s Office of Law Enforcement. The group that did so was the Washington Department of Fish and Wildlife Marine Mammal Investigations.