Footage captured by Sea Shepherd showed workers of Kristjan Loftsson's company, Hvalur hf, posing with an unconfirmed species of whale that they killed.
It is the 22nd endangered whale killed and butchered for export to Japan by commercial whaling company Hvalur hf at its station in Hvalfjordur since June 20 this year, Sea Shepherd reports.
Gísli Arnór Víkingsson at the Iceland Marine Institute, said: "We heard about this odd whale straight away and an employee reports that it's in many ways similar to a hybrid which has been brought to us quite a lot recently which is unusual".
He said there will be DNA testing to confirm the identity of the whale, but that he is not concerned by what the results might show. Humane Society International's Senior Marine Scientist, Mark Simmonds OBE, believes the whale to be a juvenile blue whale or, conceivably, a rare fin whale-blue whale hybrid.
"It is like a fin whale, it behaves like a fin whale, but after you shoot it you notice [the characteristics] are different to a fin whale".
"It seems to me like they've really stuffed up, done something really stupid and all of a sudden the focus of the world is on them".
A massive whale, believed to be a blue whale, slaughtered in Iceland, is being butchered.
Only DNA testing can prove that a whale is a hybrid.
"The killing of such a majestic creature, blue whale or hybrid, represents a significant crime against nature, given the rarity of these species and the threats to their survival today".
Campaign group Hard to Port published the photo and documented the killing on Monday via Facebook.
"This is an unacceptable tragedy that leaves people around the world speechless", Hard To Port CEO Arne Feuerhahn told Newsweek in a statement.
The whale meat being cut up on the side of the dock.
Conservation groups including Environmental Investigation Agency have described Mr Loftsson as a "multi-millionaire rogue" whaler, who is perpetuating an unpopular operation in Iceland.
"I'll come back to Brisbane when you start serving whale meat in your restaurants".
Although the first 21 whales killed were Fin whales - which the Icelandic government has permitted Loftsson's company to slaughter despite an worldwide moratorium on whaling and the endangered status of the Fin whale - they do not have any legal authority to kill endangered Blue whales, even within Iceland, alleges Sea Shepherd.