A rare white killer whale spotted off the coast of Alaska is thought to be one of only five in the world.
Named Tl’uk, the two-year-old pale male was swimming alongside a pair of adult orcas when he was identified by whale watchers on August 7.
Footage of Tl’uk was captured near Kuiu and Kupreanof Islands, which is west of Petersburg, Alaska.
A charter group was aboard Alaska Sea Adventures’ Northern Song when the whale’s white colouring shone through the water’s surface.
“When [orcas go] underwater, usually they disappear and are very hard to follow,” Sea Adventures owner Dennis Rogers told radio station KFSK.
“But having a white one under the water, you could see him an easy ten feet below the surface, this big white shape moving along there.”
White killer whales are incredibly rare. Their unusual colouration is caused by leucism, a condition that results in partial loss of pigmentation.
That makes them different to albinos, a condition which results in the complete loss of pigmentation, including the eyes.
Up to 10 – and as few as five – leucism orcas are thought to exist in the wild.
Tl’uk and his pod have been sighted frequently in British Columbia and Washington state, but never in Alaska.
Video of the whale was captured by first mate Stéphanie Hayes, a marine biologist at the University of Alaska Fairbanks, and posted to Instagram.
“A once in a lifetime sighting, killer whales with leucism are incredibly rare and even researchers never expect to see one in their career,” she wrote in her post last week.
“Tl’uk appears to be a healthy member of his pod, and we welcome him on his first documented sighting in Alaska.”
Researchers nicknamed him Tl’uk, the Coast Salish word for “moon”, because of his lunar-like grey color.
As well as his unusual colour, the whale has intricate markings near his dorsal fin that make him easy to identify.
“I saw kind of a glow under the water and I’m thinking, wow that’s an awfully white killer whale, that’s doing something funny,” Stéphanie said.
“And no, it was just genuinely the white killer whale.
“It popped up and you could hear an audible gasp from everybody on the bow, going oh my gosh what are we seeing here. It was really incredible.”