Silky Shark - Distribution and Habitat

Distribution and Habitat

The silky shark has a cosmopolitan distribution in marine waters warmer than 23 °C (73 °F). In the Atlantic Ocean, it is found from the U.S. state of Massachusetts to Spain in the north, and from southern Brazil to northern Angola in the south, including the Mediterranean Sea, Gulf of Mexico, and Caribbean Sea. It occurs throughout the Indian Ocean, as far south as Mozambique in the west and Western Australia in the east, including the Red Sea and the Persian Gulf. In the Pacific Ocean, the northern extent of its range runs from southern China and Japan to southern Baja California and the Gulf of California, while the southern extent runs from Sydney, Australia to northern New Zealand to northern Chile. Based on life history differences, four distinct populations of silky sharks have been identified in ocean basins worldwide: in the northwestern Atlantic, in the western and central Pacific, in the eastern Pacific, and in the Indian Ocean.

Primarily an inhabitant of the open ocean, the silky shark is most common from the surface to a depth of 200 m (660 ft), but may dive to 500 m (1,600 ft) or more. Tracking studies in the tropical eastern Pacific and northern Gulf of Mexico have found that cruising silky sharks spend 99% of their time within 50 m (160 ft) of the surface, and 80–85% of their time in water with a temperature of 26–30 °C (79–86 °F); the pattern was constant regardless of day or night. This species favors the edges of continental and insular shelves, often over deepwater reefs and around islands. Its range extends farther north and south along continental margins than in oceanic waters. On occasion, it may venture into coastal waters as shallow as 18 m (59 ft). Silky sharks are highly mobile and migratory, though the details of their movements are little-known. Tagging data have recorded individual sharks moving up to 60 km (37 mi) per day, and covering distances of up to 1,339 km (832 mi). Larger sharks generally move longer distances than smaller ones. In the Pacific Ocean and possibly elsewhere, it spends the summer at slightly higher latitudes, particularly during warmer El Niño years. In the northern Atlantic, most sharks follow the Gulf Stream northward along the U.S. East Coast. In the Gulf of Aden, it is most common in late spring and summer.