An all-white adult orca has managed to survive into several years in adulthood.
Killer whales, as they are also known, that are all white rather than their trademark black and white have been seen before.
But they have usually been immature or adolescent animals and it is thought they have a tendency to die young as the trait can be associated with health problems.
Conservation group Russian Orcas posted a photograph of the male orca on their Facebook page:
The whale is believed to be at least 22 – as he was already mature when he was last spotted in 2010.
He was named Iceberg with the researchers resisting temptation to reference the most famous, if fictional, white whale, Moby Dick.
The sighting was made in August last year, but has only just been revealed in an academic paper in the journal Aquatic Mammals.
Writing on Facebook, Russian Orcas said: “Iceberg the big all-white male orca was re-sighted August 2015.
“Iceberg is still travelling with his family of fish-eating orcas, but he isn’t the only all-white orca: we’ve now recorded at least five and maybe up to eight different white killer whales.
“Russian waters appear to be the world’s number one area for white killer whales who may be leucistic (patchy white pigmentation) or true albinos.
“It’s a dubious honour. As reported in our paper, albinism probably indicates inbreeding of small populations.”
Iceberg was spotted by an American, Dr Erich Hoyt, who works with Russian Orcas, near Russia’s Kuril Islands to the north of Japan.
He also made the first sighting of the whale in 2010, off the coast of Kamchatka in eastern Russia.
Speaking to the BBC in 2012, Dr Hoyt said: “We've seen another two white orcas in Russia but they’ve been young, whereas this is the first time we've seen a mature adult.
“It has the full two-metre-high dorsal fin of a mature male, which means it's at least 16 years old – in fact the fin is somewhat ragged, so it might be a bit older.
“Iceberg seems to be fully socialised; we know that these fish-eating orcas stay with their mothers for life, and as far as we can see he's right behind his mother with presumably his brothers next to him.”
Orcas are immature until about 15 and the males can live for up to 60 years.
The reasons behind Iceberg's white colouring are unclear.
The colouring of a captive white orca called Chimo was the result of Chediak-Higashi syndrome, which also caused several medical problems. She only lived to four despite females being able to live until 100.
