Shortfin Mako

Given this shark's relative notoriety, particularly among anglers, surprisingly little is known of its biology (9). Reproductive knowledge of this solitary species is sparse, largely because pregnant females usually abort embryos upon capture, making study difficult (3). Reproduction is ovoviviparous, with embryos being nourished in the uterus by a yolk sac rather than placenta. Once the young have hatched, uterine cannibalism known as oophagy occurs, in which the growing young feed on unfertilised or less-developed eggs (3). Litters of between 4 and 25 live young are born in the late winter and early spring, after a 15 to 18 month gestation period. This is followed by an initial relatively fast growth rate (2) (5) (7). Females are believed to rest for 18 months after birth before conceiving again (7). Females appear to become sexually mature at around 17 to 19 years of age and males mature around 7 to 9 years. The maximum known age of a shortfin mako is 32 years (8). The shortfin mako primarily feeds on a wide variety of fishes, such as swordfish, tuna, mackerel, cod, sea bass, and even other sharks, including blue sharks (Prionace), grey sharks (Carcharhinus) and hammerheads (Sphyrna). However, squid, sea turtle heads, and a 'porpoise' (probably a pelagic dolphin) have also been found in the stomachs of these sharks (9).

The U.S. National Marine Fisheries Service (NMFS) has included the shortfin mako on their list of managed pelagic sharks, and reduced the number of commercial and recreational catches allowed per year by 50 percent. Although it is hoped that this measure will help to counteract declining numbers, the regulations only apply to the United States and Gulf waters, while the other populations remain as vulnerable as ever (3). A short-lived experimental longline fishery was once used to target early juveniles off California, but it was closed in 1992 due to concerns over the exploitation of immature fish. Targeting juveniles means these individuals are killed before ever reproducing, exacerbating the species' decline (9). Although currently classified only as Lower Risk / Near Threatened on the IUCN Red List 2007 (1), the shortfin mako, like any other shark, is susceptible to over-fishing if not carefully managed (9). Thus, protective measures and fishing quotas implemented by other fishing nations would greatly help to safeguard the future of this magnificent, leaping shark, for years to come.

The shortfin mako is believed to be the fastest-swimming of all sharks (4) (5) (3), thought to be capable of attaining bursts of speed of up to 35 kilometres per hour (6), and famed for making spectacular leaps of up to six metres out of the water (7) (8). The species' high tail produces maximum thrust to propel the shark rapidly forward, both in extreme bursts of speed, and for sustained, long-distance travel (3) (9). The shortfin mako also has a heat exchange circulatory system that enables the body to be warmer than surrounding water, and thus maintain a high level of activity (4). This large, stream-lined shark has a distinctively crescent-shaped caudal fin, a long, conical snout, large black eyes and razor-sharp, blade-like teeth (2) (5) (3).The upper body is a brilliant metallic blue, while the underside is snow-white, with older, larger specimens tending to be darker with reduced white areas. Juveniles are therefore generally paler than adults, and also differ by possessing a clear black mark on the tip of their snout. The shortfin mako can be distinguished from the only other mako shark, the longfin mako (Isurus paucus), not only by having shorter pectoral fins, but also by the white colouration on the underside of the snout and around the mouth, which is darkly pigmented in the longfin mako (3).

The shortfin mako is usually pelagic, but can sometimes be found close inshore. Although normally occupying surface waters down to around 150 metres, this shark has been recorded at depths of up to 740 metres (2). There is evidence to suggest that this species migrates seasonally to warmer waters (3).

This is a wide-ranging shark found in tropical and temperate waters throughout the world's oceans (3). In the Western Atlantic, the species occurs from the Gulf of Maine to southern Brazil, including the Gulf of Mexico and the Caribbean (2) (5). In the Eastern Atlantic, the distribution ranges from Norway, down past the British Isles, the Mediterranean, the Ivory Coast and Ghana to South Africa (2) (5). In the Indo-Pacific, this shark is found from East Africa and the Red Sea to Hawaii, including waters around Pakistan, India, Korea, Japan, Indonesia, Australia, Tasmania, and New Zealand (2) (5). In the Eastern Pacific, the range includes waters south of the Aleutian Islands and from Southern California, USA, to Chile (2).

Classified as Lower Risk/near threatened (LR/nt) on the IUCN Red List (1).

The shortfin mako is caught both by targeted fisheries and as significant bycatch, being the major bycatch component of tuna and swordfish fisheries (1) (3). The species' is valued for its high-quality meat, its fins are marketed for shark-fin soup in the Far East, and its liver oil is extracted to make vitamins (2) (3). The jaws and teeth are also sold as ornaments and trophies, and the hides may be processed into leather (2) (9). Sadly, the shortfin mako is also considered one of the great game fishes of the world, prized for its beauty, aggressiveness, and spectacular aerial leaps when struggling against the fishing line (3) (10). The highest recreational catches occur off southern California, the north-eastern United States, Australia and New Zealand (3). Most commercial catches are inadequately or un-recorded, and conflicting data make it difficult to evaluate the exact impact fishing is having on population numbers of this shark (1) (9). However, like other sharks, this species' relatively low reproductive capacity makes it vulnerable to population declines due to over-fishing (1). Fortunately, this shark's fast growth rate means it has a mid-range rebound potential. This, combined with its world-wide distribution and relative abundance, means that the species is currently reasonably safe from the threat of extinction (9).