A pair of Japanese whaling vessels left Friday for the northwestern Pacific aiming to catch 260 whales for \"scientific research\", a fisheries ministry official said. The Yushin Maru and Yushin Maru No. 2 departed from Shimonoseki port in Yamaguchi, western Japan, to join the mother vessel Nisshin Maru, which has already set sail, the official said. The fleet is scheduled to catch around 260 of the mammals, including 100 minke whales and 10 sperm whales, between now and early August, the official said. Commercial whaling is banned under an international treaty but Japan has since 1987 used a loophole to carry out \"lethal research\" in the name of science. Japanese whalers faced a series of high-seas confrontations with anti-whaling activists in the Antarctic Ocean, but have not so far experienced any violent resistance in the Pacific.