Japan sent a whaling fleet to the northwest Pacific for what it called a research hunt, four months after cutting short a similar mission in the Antarctic due to obstruction by activists. The three-vessel fleet, led by the Nisshin Maru, plans to catch 260 whales including 100 minkes until late August to study their stomach contents, DNA and other information, according to the Institute of Cetacean Research. The government-affiliated institute has organised such operations since 1987, citing a loophole in a 1986 international moratorium on commercial whaling which allows hunts for scientific research. Anti-whaling nations and environmentalist groups condemn the activity as a cover for commercial whaling but Japan said it is necessary to substantiate its claim that there is a robust whale population in the world. The institute said the mission would be its 18th scientific expedition to the northwest Pacific. On February 18, Japan halted a research hunt in the Antarctic Ocean for the 2010-2011 season, which had been due to run from December until March, because of obstruction by militant environmentalist group Sea Shepherd. The US-based Sea Shepherd, which says its tactics are non-violent but aggressive, hurled paint and stink bombs at whaling ships, snared their propellers with rope, and moved its own boats between the harpoon ships and their prey. The four-ship fleet killed 172 whales in that season, only about a fifth of its target, the fisheries agency said at that time. Australia which last year launched legal action against Japan\'s whaling programme at the International Court of Justice and New Zealand said they hoped Japan had given up whaling for good. The institute told Japanese media that there has been no instance of obstructive activities in the northwest Pacific so far but that \"we cannot automatically consider the area safe.\"