Bigeye Thresher

The bigeye thresher shark is instantly recognizable by its enormous, elongated upper caudal fin—nearly as long as the rest of its body—and its unusually large eyes, which extend onto the top of the head and aid vision in low-light conditions. It uses its whip-like tail to stun schooling fish and squid, striking prey with rapid overhead sweeps before consuming it. As a mid- to upper-level predator, it helps regulate populations of small pelagic fish and cephalopods, contributing to the structure of open-ocean food webs.

The species undertakes daily vertical migrations, spending days in deep water below 300 meters and moving toward the surface at night.

This shark occurs in tropical and temperate waters worldwide, inhabiting oceanic and coastal-shelf environments across the Atlantic, Pacific, and Indian Oceans. Its documented range spans dozens of countries, from Taiwan and Japan to Mexico, Brazil, South Africa, and Australia, reflecting its wide-ranging oceanic and semi-coastal habits.

The primary threat is fishing pressure, both targeted and incidental. The species is caught in pelagic longline and gillnet fisheries for its meat, fins, and liver oil, and is frequently taken as bycatch in fisheries targeting tuna and swordfish. Its low reproductive rate—producing few pups after long gestation—limits population recovery.

Conservation measures include listing under CITES Appendix II, which regulates international trade, and prohibitions or retention limits in some regional fisheries management organizations. Enforcement and monitoring remain inconsistent across its range.

Population trends are currently decreasing, and continued fishing mortality across much of its distribution suggests ongoing decline unless management measures are more broadly implemented and enforced.