Thresher shark

What it is

Thresher sharks belong to the family Alopiidae and are characterised by an extremely long upper lobe on their caudal fin. This tail can reach two thirds of their total body length, resembling a scythe. The common thresher is the largest species, growing up to 6.1 metres. They have slender bodies, short heads, and cone-shaped noses. Their colour varies from greenish to brown or blue on top, fading to lighter shades underneath. Despite their size, they do not pose a threat to humans.

Where it lives

These sharks inhabit all temperate and tropical oceans globally. They are primarily pelagic, preferring open waters but often staying above 550 metres deep. Common threshers frequent continental shelves in the North Pacific. Bigeye and pelagic species dominate warmer central and western Pacific regions. Sightings have occurred in the Gulf of Mexico at unusual depths and in the western Mediterranean, suggesting wider distribution than previously recorded.

How it lives

Threshers are solitary hunters that occasionally group in twos or threes. They feed on schooling fish like tuna and mackerel, as well as squid and crustaceans. To catch fast prey, they whip their long tails through schools to stun victims. They are highly migratory and capable of breaching, jumping entirely out of the water using their powerful tails for propulsion. Some populations show sex-based separation by depth and space.

Breeding and life cycle

Reproduction is ovoviviparous, meaning young develop internally and are born live. Litters are small, usually containing two to four pups. Newborns are large, reaching up to 150 centimetres. Inside the womb, embryos consume unfertilised eggs provided by the mother, a process called oophagy. Sexual maturity is slow, occurring between seven and fourteen years depending on sex and species. Lifespans exceed twenty years.

Fish and people

Thresher sharks are targeted by commercial fisheries for meat, fins, liver oil, and skin used for shagreen. They are also popular game fish in the United States, South Africa, and off Baja, Mexico. Recreational fishing is common in these areas. While hunted extensively, they are not considered dangerous to people. Conservation concerns arise due to their low reproductive rates making them susceptible to overfishing.

Status and threats

All three recognised species are listed as vulnerable by the International Union for Conservation of Nature since 2007. Their vulnerability stems from slow maturation and low fecundity, resulting in few offspring. These biological traits make recovery from population declines difficult. Overfishing poses the primary threat to their survival across their global range.

Relatives and look-alikes

The genus Alopias contains three extant species: the common, bigeye, and pelagic thresher. A potential fourth species exists in the eastern Pacific but remains undescribed. Phylogenetic studies place them as a sister group to basking sharks and mackerel sharks. The megamouth shark is another close relative, though its exact position is less certain.

Questions people ask about Thresher shark

Good reading and sources

• Thresher shark on WikipediaEncyclopedia
• More photos on Wikimedia CommonsPhotos
• Wikidata recordOpen data