Two Japanese whaling ships and a surveillance ship left a port in western Japan on Saturday to hunt whales for scientific research in the Antarctic Sea.
The three ships departed from Shimonoseki, Yamaguchi Prefecture, to join the mother vessel Nisshin Maru and hunt up to 935 Antarctic minke whales and up to 50 fin whales through March.
The Fisheries Agency had kept secret the departure date of the whaling fleet as a precaution against obstruction by the U.S.-based antiwhaling group Sea Shepherd Conservation Society, which the surveillance ship will monitor.
Last year, Japan also sent a special ship for preventing obstruction by the antiwhaling group and is expected to do so again this year.
Sea Shepherd has in the past run interference by ramming its boat into a Japanese whaling ship and hurling rope around another's propeller.
During the last whaling season, Japan captured 103 Antarctic minke whales, the smallest catch since it began what it calls research whaling in the Antarctic Ocean in 1987, due to the antiwhaling group's activities and bad weather.
Japan, which has a long history of whaling, began the practice after the International Whaling Commission placed a zero-catch limit on commercial whaling in 1986.
Environmentalists have condemned the activity as a cover for commercial whaling.