In Star Trek IV: The Voyage Home, which extinct animals must Kirk's crew retrieve?

In Star Trek IV: The Voyage Home, Kirk's crew must retrieve humpback whales.

The crew travels from the 23rd century to San Francisco in 1986 after an alien probe begins emitting destructive signals toward Earth. Spock determines that the probe is attempting to communicate with humpback whales, a species extinct by the crew's time.

Admiral James T. Kirk and his companions therefore search for two whales, George and Gracie, at the Sausalito Cetacean Institute. They enlist marine biologist Dr. Gillian Taylor, who is frustrated by the planned release of the whales into the wild and eventually helps the visitors protect them.

The film combines time-travel comedy with an environmental message. Kirk's crew transports the whales and Dr. Taylor into the future, where their presence answers the probe's call and prevents Earth's destruction. Humpback whales were a real endangered species in the 20th century, making the story's conservation theme especially direct.