Six dead seals, including one endangered species, have washed ashore near Seattle in less than two weeks.

They had all been shot.

Brian Gorman of the National Marine Fisheries Service said the first seal carcass was reported on Feb. 1. Four seals are California sea lions, another is a harbour seal and the sixth is an endangered Steller seal lion.

"We have recovered bullets from five of them," he said. "We haven't recovered bullets from the fourth California sea lion, but there is apparently a path from a bullet and it seems it was also shot."

Conservation officers in Canada say they have no recent report sof a shot seal in British Columbia waters.

Robin Lindsey, a wildlife photographer and founder of the non-profit awareness group Seal Sitters, took a call from the owners of a private beach after an enormous seal carcass washed onto their property.

"I saw what I thought was a very large California seal lion—biggest I've ever seen," Lindsey said.

"In truth, it was a Steller sea lion, the largest seal there is."

Lindsey said she felt heartache at the sight of the dead male Steller sea lion, which appeared to be between eight and 10 years old and weighing more than 500 kilograms.

Steller sea lions are protected under U.S. federal endangered species laws.

Lindsey couldn't tell the animal had been shot, but called marine biologists who performed a necropsy on the sand. Lindsey said she knows of only three dead seals to wash up in West Seattle since 2007.

In the U.S., it is a federal offence to shoot a sea lion except in instances of self-defense. There is no seal hunting season in Washington state.

"These animals appear to have been dead for a week or more when we examined them. It's not clear when and where they were shot or even if they were shot at the same time or the same location," said Gorman.

"In fact we are getting reports of floating carcasses of California sea lions in that area even now," he said. "At least three or maybe more. Whether those have been shot remains to be seen."

The U.S. Humane Society is offering an award of $2,500 for information that leads to an arrest and conviction.

For more information about seals in Puget Sound, click here.