The 2009 documentary about dolphin hunting in Taiji, Japan that won the Oscar is The Cove.
Directed by Louie Psihoyos, The Cove investigates the annual dolphin drive hunts in Taiji, a Japanese coastal town. The film follows Ric O'Barry, a former dolphin trainer who later became an activist, as he and a team attempt to document activity in a restricted cove.
Because access was tightly controlled, the filmmakers used concealed high-definition cameras, underwater microphones, and equipment disguised as rocks. The documentary connects the hunts to debates over captivity, conservation, fishing practices, and the health risks associated with mercury in dolphin meat.
The Cove won Best Documentary Feature at the 82nd Academy Awards, held in 2010. It is often confused with Blackfish, another well-known animal-focused documentary, but Blackfish examines captive orca performances and was not the Oscar winner for this subject.