Japan's main whaling company has released images showing the first fin whale caught commercially by its fleet in almost 50 years before it was butchered and sent home for consumption.

Japan, one of three countries to hunt whales commercially with Norway and Iceland, this year added the fin whale to a catch list that already includes minke, Bryde's and sei whales.

Fin whales are the world's second-biggest animal after the blue whale.

The footage provided to AFP on Wednesday shows the dead whale being hauled up into Japan's new whaling "mother ship" as workers posed next to the carcass and readied big knives to dismember it.

Fin whales are deemed "vulnerable" by the International Union for Conservation of Nature and Japan's decision to catch them has alarmed conservationists.

"This is the first fin whale catch in Japanese commercial whaling since 1976, almost half a century ago," said Masuo Ide, spokesman for whaling firm Kyodo Senpaku, calling it the "king of whales".

The male whale, which was harpooned and killed by a smaller vessel on August 1, was 19.61 metres (64.3 feet) long and weighed at least 55 tonnes, he told AFP. Four more have been caught since.

The crew of the Kangei Maru, a 9,300-tonne mothership launched in May, butchered the carcass and stored its meat in frozen containers on board for later consumption in Japan.

Some of the fin whale meat was served in a business exhibition in the northern city of Sapporo last week, with a wholesaler telling local media it was "delicious, with no smells. It changed my impression of whale meat".

The whaling company is planning another tasting event in Tokyo on Friday.

'Scientific'

Japan has hunted whales for centuries and the meat was a key source of protein in the years after World War II.

It carried on for "scientific" purposes after an International Whaling Commission (IWC) moratorium on commercial whaling, killing hundreds -- including several fin whales -- in the Antarctic and North Pacific.

However, after years of tensions that took a toll on its international reputation, Japan quit the IWC in 2019 and resumed commercial whaling inside its territorial waters and exclusive economic zone (EEZ).

The government has allowed whalers to catch up to 376 whales this year, a number it says is sustainable, including 59 fin whales out of an estimated 19,299 fins in its waters and EEZ.

Japan is meanwhile seeking the extradition of US-Canadian anti-whaling activist Paul Watson, 73, who was detained in Greenland in July.

Watson co-founded Sea Shepherd, whose members played a high-seas game of cat-and-mouse with Japanese whaling ships in the 2000s and 2010s.

His new organisation, the Captain Paul Watson Foundation, says that its vessel was on its way to intercept the Kangei Maru when Watson was arrested.