The country's Fisheries Agency, the Institute of Cetacean Research and whaling company Kyodo Senpaku declined to comment on the fleet's schedule or why the departure has been delayed, the Japan Times reported Thursday.
Wakao Hanaoka of Greenpeace Japan said the delay is probably due to problems securing a refueling ship.
"Kyodo Senpaku lost the refueling ship it had been using, and it is difficult to find a ship owner who will take the risk of being associated with internationally condemned whaling activities," Hanaoka said.
Senpaku may shorten this year's hunt if it can't find a new refueling ship, Hanaoka said.
The whaling fleet normally arrives in the Antarctic Ocean in late November to mid-December and returns in March, arriving back in Japan in April.
As inventories of frozen whale meat have increased in Japan, the country faces increasing international pressure to cut down on whaling.
In April, the International Whaling Commission submitted a proposal for Japan to decrease its Antarctic whaling quota from the current 800 whales to about 200 in 10 years.