A humpback whale, Megaptera novaeangilae, waving its fin(s) before slapping as viewed from a Captain John's whale watch trip out of Plymouth, Massachusetts, USA. All sightings were off Provincetown, MA. Hunted nearly to extinction in the days when whale oil lit many American homes and whalebone lined ladies’ corsets, humpback whales fell far below their historic numbers of 125,000. Today 10,000 endangered humpbacks roam the world’s oceans, feeding on fish and tiny crustaceans known as "krill," which they strain out of the water with the baleen plates in their mouths. These massive mammals are up to 50 feet or more in length and may weigh as much as 37 tons, a size that is only possible for an animal living in water. Their vocalizations are the most complex in the animal kingdom and include individually recognizable songs. A major threat to humpbacks today is the decline in fish and krill populations worldwide, due to non-sustainable fishing practices.