Japan says it will abide by a Monday ruling from the United Nations' International Court of Justice ordering the nation to stop hunting whales off Antarctica.

Japan had long claimed that its program to take minke, fin, and humpback whales in the waters surrounding Antarctica (referred to in the ruling as the Southern Ocean) was aimed at collecting scientific data.

But the International Court of Justice (ICJ), headquartered at the Hague in the Netherlands, found that the program was not scientific in nature and that it could be considered commercial whaling.

The International Whaling Commission (IWC) banned commercial whaling in 1986, and most countries participating in the IWC, including Japan, have said they will follow that ban.

"Japan is disappointed and regrets" today's ruling, according to a statement by the chief cabinet secretary of Japan. "However, Japan will abide by the Judgment of the Court."

Until now, Japan had continued taking whales under a provision of the 1986 ban known as Article Eight, which allowed the killing of whales for scientific purposes. (See: "Anti-Whaling Activists Put Focus on Complex Law and Bloody Tradition.")

"It's a huge victory," Leigh Henry, senior policy advisor for wildlife conservation at the World Wildlife Fund (WWF), said of Monday’s ruling, which goes into effect immediately. "We've been fighting this battle for over three decades with little results."

"Essentially, [Japan] was exploiting this loophole" in the whaling ban, Henry said. (Related: "Whale Hunting to Continue in Antarctic Sanctuary.")

A Nonscientific Hunt

The suit, brought before the UN court by Australia—with support from New Zealand—alleged that Japan's whaling program was not based on sound scientific principles.

The court ruled in favor of Australia, finding that Japan had failed to address a variety of Australia's concerns, including whether nonlethal methods could be used to collect data rather than lethal methods.

Japan has said it needs to kill whales to obtain basic biological information about the animals, such as data on pregnancy rates and age at first reproduction, said Leah Gerber, a marine mammal biologist at Arizona State University in Tempe.

But "we don't need to keep killing them to do science," she said. Blubber biopsies can give researchers plenty of information on reproductive status and diet. That just requires shooting a small dart at a whale to take a plug of skin and blubber.

Once a Japanese ship lands a whale, there is some semblance of scientific activity, including collecting organs for use in research, Gerber said. But the bulk of the whale goes to market, she said, where it's sold for consumption.

The court said that Japan also failed to justify their sample sizes—850 minke whales, plus or minus 10 percent; 50 fin whales; and 50 humpbacks.

"Other aspects of JARPA II also cast doubt on its characterization as a programme for purposes of scientific research," the court said, referring to the name of the Japanese program, "such as its open-ended time frame, its limited scientific output to date, and the absence of significant co-operation between JARPA II and other related research projects."

Should Japan later decide not to abide by the ICJ's ruling, enforcement options are limited. But enforcement measures could include pressure from other governments in the form of economic sanctions.

Smaller Marine Mammals Still Hunted

This decision affects Japan's taking of big whale species—which include humpbacks, fins, and minke whales—since the 1986 whaling ban applies only to medium-size and large whales.

Smaller relatives, like dolphins and porpoises, are still subject to hunting. Thus Japan's controversial take of dolphins in Taiji Cove can continue. (See: "Pictures: Scenes From Taiji Dolphin Roundup in Japan.")

Japan is not the only country that has continued its whaling practices. Norway, also part of the IWC, opted out of the 1986 moratorium on commercial whaling. (See which countries continue to hunt whales.)

Called "taking a reservation," Norway continues to hunt whales, but does so according to sustainability guidelines provided by the IWC, said Henry.

Iceland dropped out of the IWC after the 1986 ban, but rejoined two years later and opted out of the moratorium. The country has continued to hunt whales and doesn't follow sustainability guidelines, Henry said.

A coalition of wildlife groups have submitted a formal request, called a Pelly petition, to the U.S. government to cite Iceland for its whaling activities.

Some IWC member countries take whales as part of subsistence hunts. "That's allowed by the IWC and is very well managed and overseen by the IWC," said Henry. Canada participates in the subsistence hunts, but is not part of the commission. (Read "Last of the Viking Whalers" in National Geographic magazine.)