The Whale Skeleton is an Easter Egg in GTA V. It consists of a large skeleton of a whale which can be found at the bottom of the ocean.
Off of the west coast of Banham Canyon, the skeleton of a whale can be found on the sea floor, partially embedded into the sand.
Players initially believed that the skeleton was actually that of a sea monster, or some other fictitious sea creature, but it has been proven that the skeleton is from a whale. It can be seen as a sort of acknowledgement of GTA fans and their search for mysterious creatures.
The whale's skeleton closely resembles that of a Humpback Whale, which is common along the Califoria coast.