AY Honors/Species Account/Isurus oxyrinchus

The shortfin mako shark, Isurus oxyrinchus ("sharp nose"), is a large shark of the Lamnidae family. Along with the closely related longfin mako, Isurus paucus, it is commonly called just mako shark.

Anatomy and appearance

This species has an average full-grown length of 1.82–2.8 m (6–9.2 ft) and weight of approximately 200 kg (440 lb). The largest reported mako was said to be 1,000 kg (2,200 lb) and 4 m (13.2 ft), although the largest confirmed size is 3.96 m (13 ft) and 794 kg (1,750 lb). It has a bluish back and white underside. Although the sexes grow at about the same rate, females are thought to have a longer life span, and grow larger and weigh more than the males. Shortfin makos are renowned for their speed and their ability to leap out of the water. In fact, there are cases when an angry mako will jump out of the water and into the boat after it has been caught on the hook. Mako sharks have a better hydrodynamic shape than all other sharks, and this, combined with the lamnidae's typical high aerobic muscle mass, reflects in the spectacular speed and agility of both the longfin and shortfin makos.

The shortfin mako shark is a sleek spindle shaped shark with a long conical snout. This shark has short pectoral fins and a crescent shaped caudal (tail) fin. There is a distinct caudal keel on the caudal base. Its second dorsal fin is much smaller than the first. The teeth are slender and are curved with no lateral cusps and are visible even when the mouth is closed. There is marked countershading on this shark; dorsally it is a metallic indigo blue while ventrally it is white.

Naming

The name "mako" comes from the Māori language, meaning either the mako shark or a shark tooth. It may simply have originated from a dialectal variation as it is similar to the common words for shark in a number of Polynesian languages - makō in the Kāi Tahu Māori dialect, mangō in other Māori dialects, ma'o in Tahitian, and mano in Hawaiian. The first written usage is in Lee & Kendall's Grammar and vocabulary of the language of New Zealand (1820), which simply states "Máko; A certain fish". Richard Taylor's A leaf from the natural history of New Zealand (1848) is more elaborate: "Mako, the shark which has the tooth so highly prized by the Maoris".

Diet

A close-up of a shortfin mako shark's head.

The shortfin mako feeds mainly upon bony fishes including mackerels, tunas, bonitos, swordfish, and sailfish, but it may also eat other sharks, porpoises, sea turtles, and herons. In Ganzirri and Isola Lipari, Sicily, shortfin makos have been found with amputated swordfish bills impaled into their head and gills, suggesting makos are making the swordfish a major food source during late spring and early summer, corresponding to the swordfish's spawning cycle. This shark, like others, has a natural predatory instinct to attack prey while they are most vulnerable.

An analysis of the stomach contents of 399 male and female mako sharks ranging from 67 to 328cm suggest makos from Cape Hatteras to the Grand Banks prefer bluefish to any other food source. In the study, Bluefish constituted 77.5% of the diet by volume. The average capacity of the stomach was 10% of the body weight. Shortfin makos consumed 4.3 to 14.5% of the available bluefish between Cape Hatteras and Georges Bank.

Shortfin makos over 3m (10 ft.) have been found to have anterior teeth considerably wider and flatter than smaller makos, which enables them to prey effectively upon dolphins, swordfish, and other sharks.

In recent years it has been suggested that adult makos infrequently attack free-swimming dolphins. This hypothesis appeared validated when an amateur video, taken in Pacific waters, emerged, showing a moribund spotted dolphin whose tail was almost completely severed, just after a shark attack. The video shows a very large shortfin mako circling the dying dolphin. Makos also have the tendency to scavenge on long-lined and netted fish.

Distribution

The shortfin mako is found in offshore temperate and tropical seas worldwide. The closely related longfin mako shark, Isurus paucus, is found in the Gulf Stream or warmer offshore waters.

It is a pelagic species that can be found from the surface down to depths of 150 m (490 ft.). The shortfin mako is found in blue waters, normally far from land though occasionally closer to shore, particularly around islands or inlets. One of only four known exothermic sharks, it is seldom found in waters colder than 16° C (61° F).

In the western Atlantic it can be found from Argentina and the Gulf of Mexico to Browns Bank off of Nova Scotia. In Canadian waters these sharks are not abundant as they prefer warm waters, but neither are they rare. Shortfin makos are often found in the same waters as swordfish as they are a source of food and both fish prefer similar environmental conditions.

It is suggested shortfin makos travel long distances to seek adequate prey or fitting mates. In December 1998, a female shortfin mako tagged off California was captured in the central Pacific by a Japanese research vessel, meaning this fish traveled over 1,725 miles (2,780 kilometers).

Behaviour

The shortfin mako's speed has been recorded at 50km/h (31 mph), and there are reports that it can achieve bursts of up to 74km/h (46mph). It can jump up to 9m (28ft.) in the air. Due to its speed and agility, this high-leaping fish is sought as game worldwide. This shark is highly migratory. Its exothermic constitution partly accounts for its relatively great speed.

There is still some uncertainty about its lifespan, but it is suspected to reach ages of between 11 to 23 years.

The shortfin's aggressive behavior could be responsible for attacks on humans, but humans cause much more harm because the demand for the meat of this fish is so high. Like other lamnid sharks, the shortfin mako has a heat exchange circulatory system that allows the shark to be seven to ten degrees warmer than the surrounding water. This system enables the shortfin to maintain a high level of activity. This could be the reason for their great hunting abilities. The higher body temperature give the sharks an advantage over its cold-blooded prey.

Reproduction

The shortfin mako shark is a yolk-sac ovoviviparous shark, meaning it gives birth to live young who feed from a sac full of yolk in the womb. The gestation period for a mako shark is 15 to 18 months. Shortfin mako embryos in the female's body consume each other to get nutrients. This is called intrauterine cannibalism.

Female shortfin makos usually become sexually mature at a length of 3 m. Developing embryos feed on unfertilized eggs in the uterus during the gestation period of 15 to 18 months. The 4 to 18 surviving young are born live in the late winter and early spring at a length of about 70 cm, but have no placental connection during development (ovoviviparity). It is believed that females may rest for 18 months after birth before the next batch of eggs are fertilized.

Male shortfin makos reach sexual maturity within 4 years.

One study conducted by NOAA in 1997, showed times at liberty ranged from 13 days to 12.8 years. This phenomenal 12.8 year recapture was in 1997 the longest time at liberty for any mako. Along with the shark itself a piece of the backbone was collected to confirm the age estimates. The recapture of this shark proved that shortfin makos can in fact live at least 13 years. This information can in turn be used to better manage the species.

Distinguishing characteristics

• Teeth are visible even when the mouth is closed
• Teeth are long and slender with smooth-edged cusps
• Distinct countershading, dorsally blue and ventrally white
• Moderately short pectoral fins
• Underside of the snout is white

Captivity

Of all recorded attempts to keep pelagic shark species in captivity, the Mako has fared the poorest; even more so than the oceanic whitetip shark, the blue shark and the great white shark. The current record is held by a specimen that, in 2001, was kept at the New Jersey Aquarium for only five days. Like past attempts at keeping Isurus in captivity, the animal appeared strong upon arrival but had trouble negotiating the walls of the aquarium, refused to feed, quickly weakened and expired.

Attacks on humans

The shortfin mako does have a formidable and foreboding appearance. The ISAF statistics on attacking species of sharks purports that between 1580 and 2007, the shortfin mako has had eight unprovoked attacks on humans with two ending in fatality and twenty boat attacks.

Short fin mako sharks in popular culture

• A mako shark appeared in Ernest Hemmingway's novella, The Old Man and The Sea

References

• Template:IUCN2006 Database entry includes justification for why this species is near threatened
• Template:ITIS
• Template:FishBase species

External links

• ARKive - images and movies of the shortfin mako (Isurus oxyrinchus)
• CANADA: Record Mako Shark Caught
• Template:Marinebio
• Shortfin mako sharks can shoot through the ocean at up to 50 miles per hour, New Scientist, 7 November 2008