The thresher shark is an active strong-swimming fish that is occasionally seen leaping out of the water (2). It feeds primarily on small, schooling fish, but also fish that dwell on the ocean bottom, squids, octopi and, very rarely, seabirds (2). It uses its unique tail fin to herd fish together in tight shoals, and then stuns them with powerful swipes of the tail. Sometimes two threshers may cooperate in their attack, swimming round the school of fish in ever decreasing circles, then striking the shoal with their tails before turning to swallow their stunned or dead victims (2) (3).
Thresher sharks possess some remarkable physiological adaptations which explain their strength and endurance in a wide range of latitudes and depths. Along each of their flanks runs a strip of red muscle, which can contract powerfully for long periods, enabling the thresher shark to swim for long periods without fatigue (4). In addition, this red muscle contains a meshwork of tiny blood vessels which transfer heat back towards the body core. Retaining body heat enables the thresher shark to remain active and react quickly even in cold water (3) (4), and also results in much faster digestion, enabling it to feed again rapidly, should the opportunity arise (3).
Thresher sharks are ovoviviparous, meaning that the young develop inside a weakly formed shell within the female. The gestation period is reported to be nine months, with litters of two to seven pups born during the spring (2). Thresher sharks reach maturity at between three and eight years old, and are estimated to live for 45 to 50 years (2).