Two Japanese vessels will depart today from Setoda, Hiroshima Prefecture, to join an international study of blue and minke whales in Antarctic waters, the Fisheries Agency said.

Organized by the International Whaling Commission, the vessels will conduct visual counts of the two species southeast of New Zealand, the agency said Tuesday. It will not hunt the whales. The vessels will return to Japan on March 27.

An agency official said the study is aimed at testing the hypothesis that an increase in minke whales is hampering a recovery in the population of blue whales.

Under Japan's whaling program, conducted for what the government claims are research purposes, Tokyo dispatched five ships to the Antarctic last month to hunt some 400 minke whales.

The government claims the "lethal surveys" are indispensable for looking into the whales' age, birthrate and other specifics and that the findings will be reported to the IWC.

However, they have drawn protests from environmental groups and other entities that claim such activities are merely a guise for renewed whaling.

The agency also fueled international criticism earlier this year by expanding the species it hunts in the Northwest Pacific under another program, which it conducted from August to September, including Bryde's and sperm whales.

The U.S. is threatening to slap trade sanctions against Japan if Tokyo continues the expanded research whaling.