Blue Shark: A species of requiem shark, family Carcharhinidae, that inhabits deep waters in the world's temperate and tropical oceans. Preferring cooler waters, blue sharks migrate long distances. Although generally lethargic, they can move very quickly. Blue sharks often school segregated by sex and size, and this behavior has led to their nickname "wolves of the sea". Oceanic and epipelagic shark found worldwide in deep temperate and tropical waters.