In the Pacific, a tiny island 300 miles away from the shore hides a giant mountain beneath the waves that forms a home for thousands of plankton feeding fish. These fish attract Tuna, and the Tuna attract thousands of Sharks. This clip is from Blue Planet Series 1.

A seamount is a mountain rising from the ocean seafloor that does not reach to the water’s surface (sea level), and thus is not an island. Seamounts are typically formed from extinct volcanoes that rise abruptly and are usually found rising from the seafloor to 1,000–4,000 m (3,300–13,100 ft) in height. They are defined by oceanographers as independent features that rise to at least 1,000 m (3,281 ft) above the seafloor. [source]

A total of 9,951 seamounts and 283 guyots, covering a total of 8,796,150 km2 (3,396,210 sq mi) have been mapped but only a few have been studied in detail by scientists. [source]