The 'tail' of a Humpback whale (Megaptera novaengliae). Note: each side of the tail is called a 'fluke'. The tail is approximately fifteen feet wide (one-third of body) propelling the whale up to 20 MPH. The flukes are comprised of muscle and other tissue - no bones. Each humpback whale has unique flukes, just as humans have unique fingerprints.
On the English Strait between Greenwich Island and Robert Island - South Shetland Islands, Antarctica.