Fish & Water - Sounds Wild
Salmon Sharks

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Salmon Sharks

Beneath the waters of Prince William Sound a remarkable fish is hunting. It's a 450 pound salmon shark, more than six feet long, cruising just under the surface, its dorsal fin knifing through the water. Salmon sharks are fast moving apex predators in the north pacific, and they are aptly named for their favorite prey. Salmon sharks are fast - they're muscular and streamlined, with large efficient gills. There's another reason salmon sharks are fast swimmers - they are warm-blooded, or homeothermic - one of the few fish that regulates its body temperature regardless of the water temperature.

Most fish lose whatever body heat they generate metabolically through their gills and skin. Salmon sharks maintain a body temperature considerably warmer than the surrounding water thanks to a specialized circulatory system. Countercurrent heat exchangers in the sharks' circulatory system prevent heat from being dissipated, especially from the gills. In one study sharks in Prince William Sound maintained a body temperature of about 77 degrees, although the water temperature varied between 40 and 60 degrees. This allows these active predators of fast-moving fish to move quickly in the cold waters of the north Pacific.