The blue shark, Prionace glauca, is a carcharhinid shark which is found in the deep waters of the world's temperate and tropical oceans. They prefer cooler waters and are not found, for example, in the Yellow Sea or in the Red Sea. Blue sharks are known to migrate long distances, from New England to South America for example. Although generally lethargic, they are capable of moving very quickly if the need arises. Blue sharks are viviparous and are noted for their large litters of 25 to over 100 pups. They feed primarily on small fish and squid, although they are perfectly capable of taking larger prey should the opportunity present itself. Also, they may pose considerable danger to humans if they are encountered in large groups. They are often found in schools segregated by sex and size, and this behavior has led to their being nicknamed the "wolves of the sea".