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|Shortfin mako shark|
|Shortfin mako shark|
The shortfin mako shark (Isurus oxyrinchus—meaning "sharp nose"), or blue pointer, is a large mackerel shark. It is commonly referred to as the mako shark together with the longfin mako shark (Isurus paucus).
In 1809, Constantine Rafinesque first described the shortfin mako and coined the name Isurus oxyrinchus (Isurus means "the same tail", oxyrinchus means "pointy snout"). "Mako" comes from the Māori language, meaning either the shark or a shark tooth. It may have originated in 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, "mago" in Samoan, 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".
The Shortfin Mako is a fairly large species of shark. An average adult specimen will measure around 3.2 m (10 ft) in length and weigh from 60–135 kg (132–298 lb). Females are larger than males. The largest shortfin mako shark taken on hook-and-line was 600.32395 kg (1,323.4878 lb), caught off the coast of California on June 4, 2013. Larger specimens are known, with a few large, mature females exceeding a length of 3.8 m (12 ft) and a weight of 570 kg (1,260 lb). The longest verified length for a Shortfin Mako caught off France in September 1973, was 4.45 m (14.6 ft). A specimen caught off Italy, and examined in an Italian fish market in 1881, was reported to weigh an extraordinary 1,000 kg (2,200 lb) at a length of 4 m (13 ft). Growth rates appear to be somewhat more accelerated in the Shortfin Mako than they are in other species in the lamnid family.
The Shortfin Mako is cylindrical in shape, with a vertically-elongated tail that assists its highly hydrodynamic lifestyle. This species' color is brilliant metallic blue dorsally and white ventrally, although coloration varies as the shark ages and increases in size. The line of demarcation between blue and white on the body is distinct. The underside of the snout and the area around the mouth are white. Larger specimens tend to possess darker coloration that extends onto parts of the body that would be white in smaller individuals. The juvenile mako differs in that it has a clear blackish stain on the tip of the snout. The Longfin mako shark very much resembles the Shortfin, but has larger pectoral fins, dark rather than pale coloration around the mouth and larger eyes. The presence of only one lateral keel on the tail and the lack of lateral cusps on the teeth distinguish the makos from the closely related porbeagle sharks of the genus Lamna.
It is a pelagic species that can be found from the surface down to depths of 150 m (490 ft), normally far from land though occasionally closer to shore, around islands or inlets. One of only four known endothermic 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 neither abundant nor rare. Swordfish are a good indication of shortfin makos as the former is a source of food and prefers similar environmental conditions.
Shortfin makos travel long distances to seek prey or mates. In December 1998, a female tagged off California was captured in the central Pacific by a Japanese research vessel, meaning this fish traveled over 1,725 miles (2,776 km). Another swam 1,322 miles (2,128 km) in 37 days, averaging 36 miles (58 km) a day.
The shortfin mako feeds mainly upon cephalopods, bony fishes including mackerels, tunas, bonitos, and swordfish, but it may also eat other sharks, porpoises, sea turtles, and seabirds. They hunt by lunging vertically up and tearing off chunks of their preys' flanks and fins. Makos swim below their prey, so they can see what is above and have a high probability of reaching prey before it notices. Biting the caudal peduncle (near the tail) can immobilize the prey. In Ganzirri and Isola Lipari, Sicily, shortfin makos have been found with amputated swordfish bills impaled into their head and gills, suggesting that swordfish seriously injure and likely kill makos. In addition, this location, and the late spring and early summer timing, corresponding to the swordfish's spawning cycle, suggests that these makos hunt while the swordfish are most vulnerable, typical of many predators.
Shortfins consume 3% of their weight each day and take about 1.5–2 days to digest an average-sized meal. By comparison, the sandbar shark, an inactive species, consumes 0.6% of its weight a day and takes 3 to 4 days to digest it. An analysis of the stomach contents of 399 male and female mako sharks ranging from 67–328 centimetres (26–129 in) suggest makos from Cape Hatteras to the Grand Banks prefer bluefish, constituting 77.5% of the diet by volume. The average capacity of the stomach was 10% of the total weight. Shortfin makos consumed 4.3% to 14.5% of the available bluefish between Cape Hatteras and Georges Bank.
Shortfin over 3 m (9.8 ft) have interior teeth considerably wider and flatter than smaller makos, which enables them to prey effectively upon dolphins, swordfish, and other sharks. An amateur videotape, taken in Pacific waters, shows a moribund spotted dolphin whose tail was almost completely severed, with a very large shortfin mako circling the dying dolphin. Makos also tend to scavenge long-lined and netted fish.
Its endothermic constitution partly accounts for its relatively great speed.
Like other lamnid sharks, the shortfin mako has a heat exchange circulatory system that allows the shark to be 7–10°F (4–7°C) warmer than the surrounding water. This system enables makos to maintain a stable, very high level of activity, giving it an advantage over its cold-blooded prey.
The Shortfin Mako is the fastest species of shark. Its speed has been recorded at 50 kilometres per hour (31 mph) with bursts of up to 74 kilometres per hour (46 mph). Though scientists are still in debate over exactly how fast the shortfin mako shark can swim, some suggest that they can reach 100 kilometres per hour (62 mph). This high-leaping fish - they can leap approximately 9 metres (30 ft) high or higher in the air - is a highly sought-after game fish worldwide. There are cases when an angry mako jumped into a boat after having been hooked.
The shortfin mako shark is a yolk-sac ovoviviparous shark, giving birth to live young. Developing embryos feed on unfertilized eggs within the uterus during the 15 to 18 month gestation period - this is called (oophagy) (i.e. egg-eating). Shortfins do not engage in sibling cannibalism unlike the sand tiger shark (Carcharias taurus). The 4 to 18 surviving young are born live in the late winter and early spring at a length of about 70 centimetres (28 in). It is believed that females may rest for 18 months after birth before mating again. Last and Stevens (2009) report shortfin makos bear young on average every 3 years.
Shortfin makos, as with most other sharks, are aged by sectioning vertebrae — one of the few bony structures in sharks — and counting growth bands. The age of shortfin mako, and therefore important parameters, such as age at sexual maturity and longevity, were severely underestimated until 2006 (e.g. claims of sexual maturity at 4–6 years, claims of longevity as low as 11 years), because of a poorly-supported belief that shortfin mako sharks deposited two growth bands per year in their vertebrae. This belief was overturned by a landmark study by Natanson et al. (2006), which proved that shortfin mako sharks only deposit one band in their vertebrae per year, as well as providing validated ages for numerous specimens. Natanson et al. (2006) aged 258 shortfin mako specimens and recorded:
Bishop et al. (2006) made similar, validated age findings (median age at maturity in males 7–9 years, median age at maturity in females 19–21 years, longevity estimates 29 years and 28 years respectively) in New Zealand waters.
The seriousness of this ageing error cannot be understated. It means that fishery management models and ecological risk assessment models in use around the world were underestimating both the longevity and the age at sexual maturity in shortfin mako sharks, particularly in females, by two thirds or more (i.e. 6 years versus 18+ years), and some of these inccurate models remain in use.
In 2010, Greenpeace International added the shortfin mako shark (Isurus oxyrinchus or mackerel shark) to its seafood red list, "a list of fish that are commonly sold in supermarkets around the world, and which have a very high risk of being sourced from unsustainable fisheries."
In 2010, the Convention on Migratory Species (CMS) also added the shortfin mako shark to Annex I of its Migratory Sharks MoU. This Memorandum of Understanding, currently in effect, serves to increase international understanding and coordination for the protection of certain migratory sharks.
Of all recorded attempts to keep pelagic shark species in captivity, the shortfin 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 on arrival but had trouble negotiating the walls of the aquarium, refused to feed, quickly weakened and died.
ISAF statistics records forty-two shortfin attacks on humans between 1980 and 2010, three of which were fatal, along with twenty boat attacks. The mako is regularly blamed for attacks on humans and, due to its speed, power and size, it is certainly capable of injuring and killing people. However, this species will not generally attack humans and does not seem to treat them as prey. Most modern attacks involving mako sharks are considered to have been provoked due to harassment or the shark being caught on a fishing line. Sharks can be attracted to spear fishermen carrying a stuck fish, and may slap them with cavitation bubbles from a swift tail flick. Divers who have encountered shortfin makos note that, prior to an attack, they will swim in a figure eight pattern and approach with mouths open.
On June 3, 2013, Jason Johnston from Mesquite, Texas caught an 11-foot-long (3.35 m), 8-foot (2.44 m) circumference Shortfin mako shark, weighing 1,323 pounds (600 kg), off Huntington Beach, California. A certified weigh master called it a world record.
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