A slender open-ocean shark with a tail as long as its body, seen in blue water off the rock rather than on it.
To about 3.8 to 4.3 m total length, of which roughly half is the upper lobe of the tail. Deep blue-grey above and white below, with a small rounded head, a short conical snout, a tiny mouth set well under the head and a very large eye. The tail is unmistakable in silhouette.
Two other threshers are the confusion. The common thresher has a white patch extending up over the base of the pectoral fin; in this species the dark back runs down over the pectoral base and the white belly does not reach it. The bigeye thresher has enormous upward-facing eyes and deep grooves running back over the head.
It hunts by accelerating into a school of baitfish and whipping the long upper tail lobe over its own head to stun them. Otherwise it is a shy open-water shark, with one exception: at cleaning stations it becomes approachable and predictable, hovering for cleaner wrasse, almost always in the early morning.
It has been recorded at Revillagigedo, at Clarión and at Socorro, but the records are mostly environmental DNA and survey work rather than diver sightings, and it is an exceptional and unpredictable animal there. The only place in the world where pelagic threshers are seen reliably is Monad Shoal off Malapascua in the Philippines, where they come to shallow cleaning stations at dawn. It is listed as endangered; longline and gillnet fishing is the reason, and with only two pups in a litter it recovers very slowly.
Ratings are per location: 1 means found on most dives that look for it, 5 means a handful of records. Where enough dives have been logged the figure is calculated from them; otherwise it is an editorial estimate, and says so. We publish habitat and destination, not the dive site.