The Nisshin Maru, an 8,000-ton whaling factory ship, has been sailing southward from Japan for about two weeks and should arrive in its hunting grounds any day now: the Southern Ocean Whale Sanctuary off the coast of Antarctica.

The Japanese have been hunting whales in spite of a moratorium on commercial whaling enacted by the International Whaling Commission in 1986. And this year, for the first time in decades, they will target threatened humpbacks and endangered fin whales.

Since the moratorium began, Japan has exploited a loophole that allows member states to kill whales for scientific research. In 1987, the Japanese established the nonprofit Institute of Cetacean Research, under the supervision of the national Fisheries Agency, to conduct its research. To most observers this was a program designed to keep the whaling fleet afloat until the moratorium could be overturned.

Japan has been "researching" minke whales, sei whales, Byrd's whales and sperm whales in the Southern Ocean and the North Pacific with great effectiveness, killing more than 25,000 whales in the process. The Japanese say they are studying stock structure, feeding behavior, etc. The meat is sold commercially. The International Whaling Commission's scientific committee has objected no fewer than 20 times, saying that Japan's research program lacks scientific rigor and would not hold up under peer review.

The Japanese will attempt to take 50 fin whales, which (like the sei and sperm whales) are listed as endangered by the World Conservation Union and by the U.S. Fish and Wildlife Service. They also plan to hunt 50 humpback whales, the social and charismatic species that is a favorite of the billion-dollar worldwide whale-watching industry. They're known for "songs" that can last as long as 24 hours, and they travel across thousands of miles. A recent study by geneticists published in the journal Science estimates their pre-whaling population at 1.5 million. Today, humpbacks may number fewer than 30,000.

The killing of a whale by the most modern methods is cruel. An exploding harpoon, meant to kill quickly, rarely does more than rupture the whale's organs. The animal is winched to the side of the kill ship, a probe is jabbed into it and thousands of volts of electricity are run through it in an attempt to kill it faster, though it often takes 15 or 20 minutes for the whale to drown.

Why are the Japanese targeting these fragile species? Why are they whaling at all?

Surveys by the British polling outfit MORI show that only 1 percent of Japanese regularly eat whale meat. Only 11 percent support whaling at all. More than 4,800 tons of surplus whale meat is being stockpiled in freezers. Last year, the five large seafood companies that owned the whaling fleet and operated it for the Institute of Cetacean Research divested and got out of whaling, citing poor consumer demand. They also stopped processing and selling the meat, leaving that to the government.

Japanese officials often decry the cultural imperialism of Western nations that hunt deer and slaughter cows and yet condemn Japanese whaling. They point to a long tradition of whaling in Japan and say they limit the hunt to a sustainable level — about 1,400 whales this year.

I asked noted marine biologist Sylvia Earle what she thought of sustainable whaling. She responded: "Whales are long-lived, slow-growing wildlife, unlike domesticated animals that convert sunlight via plants to protein in less than a year. It defies logic to think that mobilizing large ships consuming large amounts of fuel with large crews traveling large distances to satisfy the tastes of a small number of consumers qualifies as a reasonable use of resources, let alone as a 'sustainable' enterprise."

But perhaps the real reasons the Japanese continue to whale have less to do with culture and more to do with fears about the imminent collapse of a major food source. Today's oceans are in great peril. We have lost 90 percent of the pelagic predator fish stocks — marlin, tuna, swordfish, great sharks — that existed in 1950. Half the world's reefs are dead or dying. A report published a year ago in Science warned that if the current trends of overfishing continue, every fishery will collapse by 2048.

The situation puts Japan in a desperate position. The Japanese depend on seafood for 40 percent of their protein. If they accept international regulation on whaling, strict controls on fisheries may follow. Joji Morishita, director for international negotiations for the Japanese government's Fisheries Agency, told the Los Angeles Times last week, "For many developing countries, whaling has become a symbol of who will dictate resource management."

Like fish, marine mammals the world over are struggling for survival. Resource management policies based on cultural traditions or national pride need to become a thing of the past. The oceans face a tenuous future. Right now is a good time for all of us to rethink how we use them.

Peter Heller is the author of "The Whale Warriors: The Battle at the Bottom of the World to Save the Planet's Largest Mammals." He wrote this commentary for the Los Angeles Times.