Australians overwhelmingly support calls for the federal government to send a customs ship to monitor Japanese whaling in the Southern Ocean, a poll commissioned by the anti-whaling activist group Sea Shepherd indicates.

The Coalition has previously been accused of backing away from a pre-election commitment to tackle whaling in the Southern Ocean, after refusing to send a specialist customs patrol vessel and instead sending aircraft to monitor the whaling, which Japan claims is for scientific purposes.

Of the 1,002 people questioned by SMS, by the polling company Roy Morgan, 76.9% said they wanted the government to “send a ship to oppose the whaling by Japan”.

A majority of Greens, Labor and Coalition voters were in favour of sending a ship. About a third ofCoalition voters opposed the proposal.

The Greens senator Nick McKim said the Coalition was backing away from the monitoring commitment made in opposition and the prime minister, Malcolm Turnbull, had refused to express anything stronger than “disappointment” about whaling on his recent visit to Japan.

“Unfortunately now that they’re in government they seem to have changed their position entirely,” McKim said.

“He might be interested to learn that nearly 70% of Liberal voters agreed that a vessel should be sent.”

The poll comes at the end of a fraught year on the issue of whaling, in which the Japanese whaling company Kyodo Senpaku was fined $1m for “wilful contempt” of the Australian federal court after breaching an order to stop killing whales.

The decision to resume whaling also flies in the face of a 2014 international court of justice (ICJ) ruling that concluded the program had no basis in science and should be halted.

Sea Shepherd’s managing director, Jeff Hansen, told Guardian Australia that Australia should be commended for taking Japan to the ICJ, and now needs to take responsibility for enforcement.

“Absolutely, we have done some incredible work in the past cleaning up to the illegal toothfish trade,” he said.

“[But] when it comes to Japan, because they’re a rich trading partner they turn a blind eye.”

Earlier this month the Australian government indicated it would consider legal action and the environment minister, Greg Hunt, and the foreign affairs minister, Julie Bishop, described Japan’s decision as “deeply disappointing” in a demarche letter issued with other nations.

Nevertheless, Japan plans to catch a reduced number of minke whales: 333, instead of 1,000.

A spokeswoman for the environment minister, Greg Hunt, said: “The government has made representations at the highest level to urge Japan not to resume whaling and we will continue to do so.

“We will also continue our efforts in the International Whaling Commission to strongly oppose commercial whaling, and to promote whale conservation.”

In 2013, when in opposition, Hunt strongly supported having a customs vessel in the Southern Ocean.

Were whaling to occur in Australian waters it would be an “utter failure in Canberra”, he said in 2013. “We’ve got blood in the water and a blind eye in Canberra. It’s completely unacceptable.”

Activists, including Sea Shepherd, accused him of backing down after the Ocean Protector was repurposed for border control in Australia’s north and another ship was not sent to replace it.