Thirteen sea lions have been found dead along the shores of Washington since September, according to reports from a wildlife welfare group.

Six of the sea lions died of gunshot wounds, four in West Seattle and two in Kitsap County, according to Seal Sitters Marine Mammal Stranding Network. The other seven died of acute trauma suspected from human interactions around Kitsap County and the Puget Sound, with one sea lion washing up decapitated, said Seal Sitters, an organization that responds to reports of dead or stranded sea lions.

Marine mammals, like sea lions, are protected in the U.S. by the Marine Mammal Protection Act, which prohibits people from harassing, hunting, capturing, killing marine mammals, or attempting to do so. Violations of the MMPA could result in fines of up to $28,520 and/or one year in prison. The 13 sea lion deaths are currently being investigated by the National Oceanic and Atmospheric Administration Fisheries.

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

Sea lion deaths increase around the time that fishing runs do, according to Seal Sitters, because fishermen and sea lions often hunt for the same food.

“Animals searching for food to survive and fishermen searching out fish for consumption or livelihood are on an annual, never-ending collision course,” according to a Seal Sitter blog post.

To combat the competition between sea lions and fishermen, the NOAA Fisheries put out suggestions for how to deter marine mammals from interfering in fishing without violating the MMPA. These include making loud noises with horns or through banging, rubber bullets, pyrotechnics and non-lethal, water-soluble paintball guns.

Sea lion deaths for the months of September to November are up six times the yearly average, Seal Sitters report, but the most dangerous months for sea lions are yet to come. The highest months for sea lion deaths, the group added, are December through February, concurrent with fishing runs.

The NOAA reported that between 1998 and 2017, as many as 700 California sea lions were found with gunshot and knife wounds, according to National Geographic. Only a few people were charged for the crimes against marine wildlife, National Geographic reported, all of them fishermen.