(CNN) A rare white orca calf has been spotted along the Washington coast, delighting whale watchers lucky enough to see him.

Tl'uk, whose name means "moon" in Coastal Salish, is already something of a local celebrity in north coastal Washington. He's been spotted a handful of times in the Salish Sea by local whale watchers and cropped up again this weekend , Island Adventures Whale Watching lead naturalist Erin Gless told CNN.

Tiny Tl'uk was first spotted in November 2018, and he's about a year old, she said. He's not an albino whale--he's more of a cloudy grey--but it's still unusual for orcas to be anything but black-and-white, a tool they use to camouflage themselves while stalking prey.

Gless said she's not sure how Tl'uk got his coloring--it worried researchers who first thought it signaled his health was declining. But nearly one year later, he's growing and packing on pounds--all signs he's in good health.

Researchers aren't sure why Tl'uk doesn't share his family's black-and-white coloring, but he appears to be in good health, steadily gaining weight and keeping up with his pod.

Tl'uk is a Bigg's killer whale, a transient type of orca that hunts seals and sea lions up and down the West coast.