Icelandic whalers may have killed an endangered blue whale, instead of the endangered fin whale they were supposed to be hunting.
Icelandic anti-whaling group Hard To Port released images of the dead whale on Facebook and said it clearly resembled a blue whale.
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"Whale 22... shows features of a blue whale (darker belly, all black baleen, bluish colour)," it said.
"Hard To Port also noticed the critical examination by [company owner] Kristján Loftsson and his staff of this particular animal."
The photos are not enough evidence alone to confirm the animal's species though, and the BBC reports DNA testing will be conducted on the whale.
Representatives for the whaling company involved have the BBC they are confident the whale killed is a hybrid between a blue whale and a fin whale.
But experts are not convinced.
Phillip Clapham, of the National Oceanic and Atmospheric Administration's Alaska Fisheries Science Centre, told the Sydney Morning Herald he does not believe it is a hybrid.
"While I can't entirely rule out the possibility that this is a hybrid, I don't see any characteristics that would suggest that," he said.
"From the photos, it has all the characteristics of a blue whale; given that - notably the coloration pattern - there is almost no possibility that an experienced observer would have misidentified it as anything else at sea."