The common thresher shark (Alopias vulpinus) is a fast-swimming shark with a distinctive appearance, recognized by the enormous upper lobe of its tail, which can equal the length of the rest of the body. It actively hunts schooling fish such as herring and mackerel, as well as occasional squid, which it stuns using its long, scythe-like tail. In Atlantic Canada, common thresher sharks are sometimes observed breaching spectacularly as they attack prey near the surface.

The species occurs worldwide, although it generally prefers temperate and cooler waters. In the Gulf of St. Lawrence, the common thresher shark has been documented for centuries[1] both near shore and in offshore waters during its seasonal migrations. Despite its impressive size and appearance, it is considered harmless to humans.

(1) Martijn, Charles, A. (1986). Les Micmacs et la mer. Recherches amérindiennes au Québec, Montréal. 343 p.

• Average length of 2 to 5 metres.
• Upper body metallic brown, grey, blue-grey, or black, with a white ventral surface.
• Short, blunt snout with relatively small jaws and teeth.
• Extremely elongated upper caudal lobe representing up to 50% of the total body length.
• Uses its long tail to stun schooling fish such as mackerel and herring.
• Seasonal presence in Atlantic Canada and Québec.
• Rare in the Gulf of St. Lawrence and absent from the Estuary.

In the Northwest Atlantic, the common thresher shark ranges from Newfoundland to the Gulf of Mexico, although it remains relatively rare in Atlantic Canada and Québec. In the St. Lawrence, the duration of its seasonal summer presence may be influenced by increasingly warm conditions associated with climate change.

The common thresher shark (Alopias vulpinus) has not yet been assessed by COSEWIC (Committee on the Status of Endangered Wildlife in Canada) and is not currently listed under Canada’s Species at Risk Act (SARA). However, the species is considered vulnerable to overfishing because of its slow growth, late maturity, and low reproductive rate.

Globally, the common thresher shark is classified as Vulnerable by the International Union for Conservation of Nature (IUCN). International concern for the species has also led to its inclusion in Appendix II of CITES, meaning international trade is monitored and regulated to help prevent overexploitation.