The long battle over Japan’s killing of hundreds of whales during its annual hunting season moved to the International Court of Justice in The Hague on Wednesday, when hearings began into an Australian suit charging Japan with unlawful practices and with using so-called research as a front for commercial whaling.

Both sides are treating the case about the world’s largest mammals as a high-stakes fight; the front rows of the courtroom were packed with lawyers and scientists from the two countries. New Zealand sent delegates to support Australia, and there were two representatives of Sea Shepherd, the conservation group based in the United States that has sent fast ships to harass and block Japan’s whaling fleet.

Australia believes that in addition to being a front for commercial activity, Japan’s “research quota” catch of up to 1,000 whales a year violates a 1946 international convention regulating whaling, as well as a moratorium on commercial activity set by the International Whaling Commission in 1986, when the number of whales had fallen sharply.

Japan has killed more than 10,000 whales since that ban went into force, according to the Australian government.