"If this were a blue whale it would be against the regulations of the worldwide whaling commision but if it's a hybrid there are no rules that have been broken. This should be a final wake-up call to Iceland that commercial whaling does not belong in the 21st century", she added. "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".
Dr Gill said the colouration, shape and size of the dorsal fin and colour of the baleen (mouth filter) were all characteristic of a blue whale.
"To mistake a blue whale for a fin whale is impossible, this whale has all the characterisations of a fin whale in the ocean".
Although the first 21 whales killed were Fin whales - which the Icelandic government has permitted Loftsson's company to slaughter despite an global 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.
'From the photos, it has all the characteristics of a blue whale; given that - notably the coloration pattern - there is nearly no possibility that an experienced observer would have misidentified it as anything else at sea'.More news: In Egypt discovered mysterious giant sarcophagus head
"Sea Shepherd volunteers monitoring the Hvalur hf whaling station in Hvalfjordur Iceland have documented the slaughter of an endangered Blue whale on the night of July 7th", the group said in a statement.
Sea Shepherd UK's Chief Operating officer Robert Read demanded that DNA samples should be taken from from all the whale meat and parts in storage at Loftsson's whaling station and warehouses.
There are about 25,000 of them and 100,000 fin whales.
The government of Iceland confirmed that "blue whales are protected under Icelandic law with their capture prohibited".
Their founder, Paul Watson, said: "This man (Loftsson) must be stopped from ruthlessly violating global conservation law and bringing such disrepute to the nation of Iceland".More news: North Atlantic Treaty Organisation survives Trump, but the turmoil is leaving scars
"Iceland's whaling is rogue and archaic and should command diplomatic criticism at the highest levels".
"I have viewed plenty of blue whales on the surface, dived with them beneath the surface in West Australia, off the coast of California, in the Southern Ocean and in the waters off Newfoundland". One has not been slaughtered for more than 50 years.
A blue whale - the largest animal to have ever lived - has not been deliberately caught since 1978, according to the International Union for the Conservation of Nature (IUCN).
Mr Loftsson said his crew spent an hour observing the whale before shooting it, and that they have never mistakenly taken a blue whale.More news: Netflix Topples HBO in Emmy Nominations
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