Alopias, the thresher sharks, belongs to family Alopiidae (order Lamniformes) and comprises three extant species: A. vulpinus (common thresher), A. superciliosus (bigeye thresher) and A. pelagicus (pelagic thresher). They are distinguished by an extra‑long upper caudal lobe used to tail‑slap and stun schooling prey.
Ecology & Behaviour
Diet: small pelagic fishes and cephalopods; cooperative encirclement and dawn/dusk foraging on bait balls are common.
Reproduction: aplacental viviparous with oophagy; low fecundity and late maturity.
Habitat use: coastal‑oceanic, mainly epipelagic to upper mesopelagic (0–200 m+); bigeye threshers frequent deeper, low‑light layers.
Identification
Elongate, streamlined body; upper caudal lobe longer than the body depth; long narrow pectorals; first dorsal fin mid‑body. Bigeye thresher has very large eyes with a distinct supraorbital groove; pelagic thresher is slimmer and more uniformly coloured; common thresher is the most robust.
Size & Longevity (genus range)
Length: commonly 2.5–4.5 m; maxima >5 m.
Weight: roughly 100–350+ kg.
Life: about 15–30+ years.
Range & Habitat
Nearly worldwide in temperate to tropical oceans—from outer shelves to the open sea—tracking fronts, upwellings, seamounts and prey aggregations.
Threats & Conservation
Fisheries pressure: significant bycatch and targeted catch in longlines, gillnets and trawls; fin/meat trade.
Intrinsic vulnerability: low fecundity and late maturity lead to slow recovery.
Management priorities: bycatch reduction (circle hooks, weak links, best‑practice release), spatio‑temporal management of hotspots, size/quotas and international cooperation. All Alopias spp. are listed on CITES Appendix II (regulated trade).
