Mystery surrounds the gruesome discovery of 13 dead sea lions which have washed up on Washington state beaches, with a marine conservation group reporting that some were either shot or beheaded.

Bullet ridden corpses of California sea lions are becoming an all too common occurrence around the waters of Puget Sound, according to The Seattle Times. Since September, a total of 13 sea lions have been found dead in the area, some bizarrely displaying gunshot wounds, with another more recent case involving a badly mutilated creature.

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A floating dead sea lion washed up on West Seattle with its head entirely gone. Clean cut. So, since 9/29, we are now at 4 confirmed shot and one apparently decapitated. This is 100% @SenatorCantwell's fault for declaring war on seals and sealions. pic.twitter.com/JXayC748QG — Diane Fraleigh 🐬 (@Casey_Pup) November 22, 2018

According to conservation group Seal Sitters, six of the 13 dead sea lions were shot, while earlier this month another animal near Alki Beach, West Seattle, was fully decapitated. Those behind the killings have yet to be brought to justice.

Officers from the National Oceanic and Atmospheric Administration are investigating the mysterious killings, which are against the law under the US Marine Mammal Protection Act.

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In North America, sea lions are killed for sport, food and also to preserve fish stocks. In the state of Washington, up to 92 sea lions are allowed to be lawfully killed by wildlife authorities. However, taking the life of one of the animals without permission is against the law and could result in a fine of more than $25,000 or a year in prison.

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