The Longfin Mako Shark (Isurus paucus) is a species of mackerel shark in the family Lamnidae. An uncommon species, it is commonly lumped together under the name "mako" with its better-known relative, the shortfin mako shark (I. oxyrinchus). The longfin mako is of limited commercial value as its meat and fins are of lower quality than those of other pelagic sharks; it is caught unintentionally in low numbers across its range. The International Union for Conservation of Nature (IUCN) has assessed this species as Vulnerable due to its rarity, low reproductive rate, and continuing bycatch mortality.
The longfin mako is the larger of the two makos and the second-largest species in its family (after the great white), reaching upwards of 2.5 m (8.2 ft) in length and weighing over 70 kg (150 lb); females grow larger than males. The largest reported longfin mako was a 4.3 m (14 ft) long female caught off Pompano Beach, Florida, in February 1984. This species has a slim, fusiform shape with a long pointed snout and large eyes that lack nictating membranes (protective third eyelids). There are 12–13 tooth rows on either side of the upper jaw and 11–13 tooth rows on either side of the lower jaw. The teeth are large and knife-shaped, without serrations or secondary cusps; the outermost teeth in the lower jaw protrude prominently from the mouth. The gill slits are long and extend onto the top of head.
The pectoral fins are as long or longer than the head, with a nearly straight front margin and broadly tips. The first dorsal fin is large with a rounded apex, and is placed behind the pectoral fins. The second dorsal and anal fins are tiny. The caudal peduncle is expanded laterally into strong keels. The caudal fin is crescent-shaped, with a small notch near the tip of the upper lobe. The dermal denticles are elliptical, longer than wide, with 3–7 horizontal ridges leading to a toothed posterior margin. The coloration is dark blue to grayish black above and white below. The unpaired fins are dark except for a white rear margin on the anal fin; the pectoral and pelvic fins are dark above and white below with sharp gray posterior margins. In adults and large juveniles, the area beneath the snout, around the jaw, and the origin of the pectoral fins have dusky mottling.
An inhabitant of the open ocean, the longfin mako generally remains in the upper mesopelagic zone during the day and ascends into the epipelagic zone at night. Off Cuba, it is most frequently caught at a depth of 110–220 m (360–720 ft) and is rare at depths above 90 m (300 ft). Off New South Wales, Australia, most catches occur at a depth of 50–190 m (160–620 ft), in areas with a surface temperature around 20–24 °C (68–75 °F).
Its diet consists mainly of small, schooling bony fishes and squids.