Shortfin mako shark
|Shortfin mako shark|
|Distribution of Isurus oxyrinchus|
The shortfin mako shark[pronunciation?] (Isurus oxyrinchus), also known as the blue pointer or bonito shark, is a large mackerel shark. It is commonly referred to as the mako shark, as is the longfin mako shark (Isurus paucus). The shortfin mako is on record as the fastest-swimming shark, capable of bursts of speed up to 18.8 metres per second (68 km/h; 42 mph).
"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 and 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". In 1809, Constantine Rafinesque gave the shortfin mako the scientific name Isurus oxyrinchus (isurus means "the same tail", oxyrinchus means "pointy snout").
The shortfin mako shark is a fairly large species of shark. An average adult specimen measures around 3.2 m (10 ft) in length and weigh from 60–135 kg (132–298 lb). The species is sexually dimorphic, with females typically larger than males. The largest shortfin mako shark taken on hook-and-line was 600 kg (1,300 lb), caught off the coast of California on June 3, 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 of the coast of France in September 1973, was 4.45 m (14.6 ft). A specimen caught off the coast of 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 accelerated in the shortfin mako in comparison to other species in the lamnid family.
The shortfin mako shark is cylindrical in shape, with a vertically elongated tail. This species exhibits countershading, with brilliant metallic blue coloration dorsally and white ventrally. 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 mako shark, 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.
Range and habitat
It is a pelagic species that can be found from the surface 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 good indicators of shortfin mako populations, as the former are a source of food and prefer similar environmental conditions.
Shortfin mako sharks 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 mi (2,776 km). Another specimen swam 1,322 mi (2,128 km) in 37 days, averaging 36 mi (58 km) a day.
The shortfin mako shark feeds mainly upon cephalopods and bony fish 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. In Ganzirri and Isola Lipari, Sicily, shortfin makos have been found with amputated swordfish bills impaled into their head and gills, suggesting swordfish seriously injure and likely kill them. In addition, this location, and the late spring and early summer timing, corresponding to the swordfish's spawning cycle, suggests they hunt while the swordfish are most vulnerable, typical of many predators.
Shortfin mako sharks consume 3% of their weight each day and take about 1.5–2.0 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 cm (26–129 in) suggest makos from Cape Hatteras to the Grand Banks prefer bluefish, constituting 77.5% of their diet by volume. The average capacity of the stomach was 10% of the total weight. Shortfin mako sharks consumed 4.3% to 14.5% of the available bluefish between Cape Hatteras and Georges Bank.
Shortfin mako sharks 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 pantropical spotted dolphin whose tail was almost completely severed being circled by a shortfin mako. 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 shark 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 them to maintain a stable, very high level of activity, giving it an advantage over its cold-blooded prey.
The shortfin mako shark is the fastest species of shark. Its speed has been recorded at 40 km/h (25 mph) with bursts of up to 74 km/h (46 mph). This speed aids in leaping, with heights of approximately 9 m (30 ft) having been recorded. These characteristics have made the shortfin mako a highly sought-after game fish worldwide. Some cases of shortfin mako jumping into a boat after having been hooked have been reported.
The shortfin mako shark is a yolk-sac ovoviviparous shark, giving birth to live young. Developing embryos feed on unfertilized eggs (oophagy) within the uterus during the 15- to 18-month gestation period. They do not engage in sibling cannibalism unlike the sand tiger shark (Carcharias taurus). The four to 18 surviving young are born live in the late winter and early spring at a length of about 70 cm (28 in). Females may rest for 18 months after birth before mating again. Shortfin mako sharks bear young on average every three years.
Shortfin mako sharks, 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 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:
- Maximum age of 29 years in males (260 cm fork length (FL))
- Maximum age of 32 years in females (335 cm FL)
- 50% sexual maturity at 8 years in males (185 cm FL)
- 50% sexual maturity at 18 years in females (275 cm FL)
Similar, validated age findings were made (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.
Due to this error, 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 inaccurate models remain in use.
Of all studied sharks, the shortfin mako has one of the largest brain:body ratios. This large brain size prompted New Zealand Sealife Australia and New Zealand senior curator Craig Thorburn of Auckland, New Zealand, and film-maker Mike Bhana to investigate the intelligence of the mako. From tests involving shape differentiation to electroreception tests and individual recognition, Isuru Somawardana and his team of shark experts discovered makos are fast-learning sharks, able to determine whether or not the researchers were threatening. The sharks involved in the study (while never the same individuals) after initial caution showed unique and never before seen behaviors, such as refusing to roll back their eyes during feeding and allowing themselves to be briefly restrained and touched while being offered bait. Shortfin makos also do not rely on electroreception when hunting, unlike the great white shark, based on tests involving wired fiberglass fish designed to emit weak electrical signals resembling real fish of similar size. Instead, they rely on smell, hearing, and most prominently, vision. The results of this research were featured on a documentary presented by Shark Week in 1999 called "The Mako Shark: Swift, Smart and Deadly".
Fishing for sport
Mako fishing is a predominant activity around the world. As one of the fastest species in the water they offer acrobatic flips, fast runs, and heavy fights that entertain anglers. Traditionally the sharks are hooked through the use of chum and baitcasters. However fly fishing for them has become more popular, particularly in San Diego, where one of the 3 known worldwide mako rookeries is located. A cottage industry of fishing in this rookery has emerged, specifically catch and release with charter operations out of Mission Bay. For many years the mass commercial boats hunted them for restaurant catch but through the efforts of many local fishing companies and national organizations such as Orvis this has been curbed.
Of all recorded attempts to keep pelagic shark species in captivity, the shortfin mako shark 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 kept at the New Jersey Aquarium for only five days in 2001. 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.
Attacks on humans
ISAF statistics records 42 shortfin attacks on humans between 1980 and 2010, three of which were fatal, along with 20 boat attacks. This 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 shortfin 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, prior to an attack, they swim in a figure-eight pattern and approach with mouths open.
The shortfin mako is currently classified as Vulnerable by the IUCN, having been uplisted from Near threatened in 2007. The species is being targeted by both sport and commercial fisheries, and there is a substantial proportion of bycatch in driftnet fisheries for other species.
On June 3, 2013, Jason Johnston from Mesquite, Texas, caught a 3.73 m (12.2 feet) long, 2.44 m circumference shortfin mako shark, weighing 1,323 lb (600 kg), off Huntington Beach, California. A certified weigh master called it a world record.
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