- International Court of Justice ruled against Japan's whaling program in 2014
- Political support for whaling remains strong in Japan, even as consumption of whale meat falls
In a statement Monday, the group's founder Paul Watson said "Japan is now employing military surveillance to watch Sea Shepherd ship movements in real time by satellite," making it nearly impossible for them to intercept them.
"We cannot compete with their military grade technology."
Last year, Japan's Institute of Cetacean Research -- a government backed organization which engages in whaling -- succeeded in obtaining an injunction against Sea Shepherd in a US court, preventing it from ramming or coming within 500 yards of its ships.
Sea Shepherd is headquartered in Amsterdam, with offices in more than 20 countries around the world.
Sea Shepherd's Australian branch maintain that the US court ruling has no jurisdiction in Australian waters and vowed to continue in its fight to expose Japanese whalers, which the group says break international law. In January its ship Ocean Warrior caught a Japanese vessel with a dead whale on board in an Australian whale sanctuary in the Southern Ocean.
But Watson said the combination of surveillance techniques, the passage of new anti-terrorism laws "specifically designed to condemn Sea Shepherd tactics," and a threat by Japan to send military vessels to defend whalers was too much.
"The decision we have had to face is: do we spend our limited resources on another campaign to the Southern Ocean that will have little chance of a successful intervention or do we regroup with different strategies and tactics?"
Japan's Ministry of Foreign Affairs and the ICR did not immediately respond to a request for comment.
In the statement, Watson called on the Australian government to step up to police its waters in the Southern Ocean, where Sea Shepherd and other groups say Japanese whalers are operating illegally.
"Instead of supporting Sea Shepherd the Australian government has been supporting the Japanese whalers by harassing Sea Shepherd and obstructing Sea Shepherd's ability to raise funds by denying our charitable status," Watson said.
Under Australian law, "it is illegal to kill, injure or interfere with cetaceans (whales, dolphins and porpoises) in Australian waters."
Japan has previously justified its whaling on an exemption in international law which allows the animals to be killed for scientific purposes, but Australia won a 2014 case at the International Court of Justice which ruled against the Japanese program in the Southern Ocean.
After the ruling however, Japan announced new research program, under which it would kill up to 333 Antarctic minke whales each year. The country's Ministry of Fisheries said the program is necessary to study the best methods of managing minke populations.
In January, Australia said it was "deeply disappointed" by Japan's decision to keep whaling and reiterated its opposition to "all forms of commercial and so-called 'scientific' whaling."
Australia's Department for Environment and Energy did not immediately respond to a request for comment regarding Sea Shepherd's statement.
While the group will suspend its most well known tactic -- Watson's hunting of Japanese whalers was featured in the hit Animal Planet show "Whale Wars" -- Sea Shepherd said it would continue its efforts "to go after and shut down whalers."
"The Japanese whalers have been exposed, humiliated and most importantly have been denied thousands of lives that we have spared from their deadly harpoons," Watson said.
"Thousands of whales are now swimming and reproducing, that would now be dead if not for our interventions."
However, despite intense international opposition to Japanese whaling, and polls showing few Japanese still regularly consume whale meat, the industry does appear to be weathering the storm.
As well as Sea Shepherd's retreat, Japan recently passed new legislation critics say opens the door to a potential resumption of commercial whaling.
In a statement, Greenpeace Japan and another 11 Japanese NGOs, said the law meant "our tax money will be spent on these wasteful programs every year, whilst damaging our relationships with otherwise friendly nations, and disgracing ourselves internationally."