More than 120 pregnant whales were slaughtered in the latest Japanese whale hunt in Antarctica’s Southern Ocean, new documents show, reigniting calls for Australia to step up efforts to stop the annual killing spree.

A further 114 immature whales were killed as part of the so-called “scientific” whaling program, according to meeting papers from the International Whaling Commission’s scientific committee meeting this month.

A minke whale is unloaded in Kushiro, a port on Japan's northern island of Hokkaido, in 2013. AP

Japan insists on conducting its annual summer whale hunt – including killing in Australian whale sanctuaries - despite international condemnation.

The latest figures show that of 333 minke Antarctic whales killed last summer, 181 were females. Some 122 females, or 67 per cent, were pregnant.

The hunt killed 61 immature males and 53 immature females – 114 in total.

Japan claims the whaling is for scientific research, yet also allows the sale of the whale flesh in markets and restaurants.

The documents show Japan characterised its latest killings as "biological sampling" that aims to investigate "the structure and dynamics of the Antarctic marine ecosystem”.

Japan claims its annual whale hunt is required for "research" purposes. Greenpeace

Once a school of minke whales was sighted, the Japanese identified one or two for killing, using “harpoons with a 30g penthrite grenade”. Whales were then transported to the research base vessel, Nisshin Maru, which had 12 “researchers” on board.

Japan claims it must obtain the stomach contents of the whales “to estimate prey composition and consumption”. Blubber thickness, fat weight and girth are purportedly required to study the animal's nutritional condition.

Body parts and organs are weighed using electronic hanging scales and skull measurements are taken using a large calliper.

In order to estimate the age of a whale, Japan says only “lethal sampling methods” are adequate. This involves examining the extent of earwax plugs that accumulate in a whale’s ears over a lifetime, which reveal its age.

The documents say Japan targeted 344 whales and killed 333. Eleven whales evaded the harpoons and escaped “into the high density sea ice”.

Humane Society International senior program manager Alexia Wellbelove said the killing of 122 pregnant whales was “a shocking statistic and sad indictment on the cruelty of Japan's whale hunt”.

"It is further demonstration, if needed, of the truly gruesome and unnecessary nature of whaling operations, especially when non-lethal surveys have been shown to be sufficient for scientific needs,” she said.

Japan conducts its annual whale hunt in the Southern Ocean despite international condemnation. Greenpeace

Ms Wellbelove said whales already faced threats such as marine pollution and commercial fishing by-catch. Australia should send “the strongest possible message to Japan that it should stop its lethal whaling programs,” she said.

Labor's environment spokesman Tony Burke said the Turnbull government "can’t continue to turn a blind eye to this. It’s appalling".

"There is nothing scientific about harpooning a pregnant whale, chopping it up and putting it on a plate. Japan’s position on this is absurd and the Australian government must not be silent," he said.

Environment and Energy Minister Josh Frydenberg said the government was "deeply disappointed" in the Japanese whaling activity.

"The government has made representations at the highest levels to Japan and will continue to do so," he said.

Mr Frydenberg said Australia had previously initiated proceedings against Japan in the International Court of Justice and was working through the International Whaling Commission to end commercial and so-called scientific whaling, as well as promoting whale conservation and seeking greater scrutiny of Japan's whale hunt.

In November footage emerged showing the brutality of a Japanese whale hunt in an Australian whale sanctuary. The federal government fought to have the footage kept secret, arguing that it would harm relations with Japan.

Before being elected the Coalition pledged to send a Customs ship to Antarctica to police the hunt, which takes place in Australian waters in contravention of international laws.

In February 2013, then opposition environment spokesman Greg Hunt accused the Labor government of "turning a blind eye to whaling in our waters ... [we] should have a Customs vessel in the Southern Ocean."

Since coming to power the Coalition has not dispatched any such vessels, but has sent a plane to conduct aerial surveys.

As Fairfax Media reported in August last year, conservation group Sea Shepherd has abandoned its annual face-off with Japanese whaling ships in Antarctic waters because it no longer had the resources to send its boats to prevent the hunt.

The Japanese embassy has been contacted for comment. It has previously said its whale program was carried out "in accordance with the International Convention for Regulation of Whaling".

Japan reportedly intends to take about 4000 whales over the next 12 years and ultimately plans to resume commercial whaling.