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The billfish are a group ( Xiphioidea) of saltwater fish predatory fish characterised by prominent pointed beak (rostra), and by their large size; some are longer than . Extant billfish include sailfish and marlin, which make up the family Istiophoridae; and swordfish, sole member of the family Xiphiidae. They are often which feed on a wide variety of smaller fish, and . These two families are sometimes classified as belonging to the order Istiophoriformes, a group which originated around 71 million years ago in the Late Cretaceous, with the two families diverging around 15 million years ago in the Late Miocene. However, they are also classified as being closely related to the and tuna within the suborder Scombroidei of the order Perciformes. However, the 5th edition of the Fishes of the World does recognise the Istiophoriformes as a valid order, albeit including the Sphyraenidae, the .
Billfish are pelagic fish and highly migratory, and are found in all oceans.Ken Schultz: Ken Schultz's Fishing Encyclopedia. 1999. "http://www.gofishn.com/content/billfish# " Although they usually inhabit tropical and subtropical waters, swordfish are also found in temperate waters. Billfish use their long spear/sword-like upper beaks to slash at and stun prey during feeding. Their bills have been known to impale prey, and have sometimes even accidentally impaled boats and people, but they are not intentionally used for this purpose. They are highly valued as game fish by sports fishermen.
The enigmatic Cylindracanthus, known from the Late Cretaceous to the Eocene, is sometimes considered a "billfish" related to blochiids on the basis of its presumed rostral spines, but no other fossils are known of it aside from its rostral spines, leading to the suggestion that it had a Cartilage body and may even be a relative of .Parris, D. C., Grandstaff, B. S. and Bell, G. L. 2001. Reassessment of the affinities of the extinct genus Cylindracanthus (Osteichthyes). Proceedings of the South Dakota Academy of Science, 80: 161–172. Similarly, the Pachycormiformes fish Protosphyraena and the Plethodidae fish Rhamphoichthys from the Late Cretaceous had both convergently evolved a highly billfish-like body plan, but are known to be very distantly related to actual billfish; these genera may have instead served as a Cretaceous ecological analogue to billfish.
| + Billfish species | |||||||||||
| Xiphiidae | Xiphias | Swordfish | Xiphias gladius (Linnaeus, 1758) | 455 cm | 300 cm | 650 kg | years | 4.49 | Xiphias gladius (Linnaeus, 1758) FAO, Species Fact Sheet. Retrieved 2 March 2012. | Near threatened | |
| Istiophoridae | Sailfish Sailfish | Atlantic sailfish | Istiophorus albicans (Latreille, 1804) | 315 cm | cm | 58.1 kg | 17 yearsArocha F and Ortiz M (2006) Description of Sailfish (SAI) ICCAT Manual. | 4.50 | Not assessed | ||
| Indo-Pacific sailfish | Istiophorus platypterus (Shaw, 1792) | 340 cm | cm | 100 kg | years | 4.50 | Istiophorus platypterus (Shaw, 1792) FAO, Species Fact Sheet. Retrieved 2 March 2012. | Vulnerable | |||
| Istiompax | Black marlin | Istiompax indica (Cuvier, 1832) | 465 cm | 380 cm | 750 kg | years | 4.50 | Data deficient | |||
| Makaira | Indo-Pacific blue marlin | Makaira mazara (Jordan and Snyder, 1901) | 500 cm | 350 cm | 625 kg | 4.5 – 6 years | 4.46 | Not assessed | |||
| Atlantic blue marlin | Makaira nigricans (Lacépède, 1802) | 500 cm | 290 cm | 820 kg | years | 4.50 | Vulnerable | ||||
| Tetrapturus | White marlin | Tetrapturus albidus/ Kajikia albida Poey, 1860 | 300 cm | 210 cm | 82.5 kg | years | 4.48 | Least concern | |||
| Shortbill spearfish | Tetrapturus angustirostris Tanaka, 1915 | 200 cm | cm | 52 kg | years | 4.50 | Data deficient | ||||
| Striped marlin | Tetrapturus audax/ Kajikia audax (Philippi, 1887) | 350 cm | cm | 200 kg | years | 4.58 | Tetrapturus audax (Philippi, 1887) FAO, Species Fact Sheet. Retrieved 2 March 2012. | Least concern | |||
| Roundscale spearfish | Tetrapturus georgii Lowe, 1841 | 184 cm | cm | 24 kg | years | 4.37 | Data deficient | ||||
| Mediterranean spearfish | Tetrapturus belone Rafinesque, 1810 | 240 cm | 200 cm | 70 kg | years | 4.50 | Least concern | ||||
| Longbill spearfish | Tetrapturus pfluegeri Robins and de Sylva, 1963 | 254 cm | 165 cm | 58 kg | years | 4.28 | Least concern |
Billfish normally use their bills to slash at schooling fish. They swim through the fish school at high speed, slashing left and right, and then circle back to eat the fish they stunned. Adult swordfish have no teeth, and other billfish have only small file-like teeth. They swallow their catch whole, head-first. Billfish do not normally spear with their bills, though occasionally a marlin will flip a fish into the air and bayonet it. Given the speed and power of these fish, when they do spear things the results can be dramatic. Predators of billfish, such as great white and mako sharks, have been found with billfish spears embedded in them. Pelagic fish generally are fascinated by floating objects, and congregate about them. Billfish can accidentally impale boats and other floating objects when they pursue the small fish that aggregate around them. Care is needed when attempting to land a hooked billfish. Many fisherman have been injured, some seriously, by a billfish thrashing its bill about.Iversen ES and Skinner RH (2006) Dangerous sea life of the west Atlantic, Caribbean, and Gulf of Mexico: a guide for accident prevention and first aid Page 77–78, Pineapple Press. .
Like Scombridae (tuna, bonito and mackerel), billfish have both the ability to migrate over long distances, efficiently cruising at slow speeds, and the ability to generate rapid bursts of speed. These speed bursts can be quite astonishing, and the Indo-Pacific sailfish has been recorded making a burst of 68 miles per hour (110 km/h), nearly top speed for a cheetah and the highest speed ever recorded for a fish.
Some billfish also descend to considerable mesopelagic depths. They have sophisticated which allow them to rapidly compensate for pressure changes as the depth changes. This means that when they are swimming deep, they can return swiftly to the surface without problems.Schultz, 2007, pp. 22–24. "Like the large tuna, some billfish maintain their body temperature several degrees above ambient water temperatures; this elevated body temperature increases the efficiency of the swimming muscles, especially during excursions into the cold water below the thermocline." See for more information about these specialized modified muscle cells.Sherwood, Klandorf, Yancey, Animal Physiology: From Genes to Organisms, 2nd edition)
In 1936 the British zoologist James Gray posed a conundrum which has come to be known as Gray's paradox. The problem he posed was how dolphins can swim and accelerate so fast when it seemed their muscles lacked the needed power. If this is a problem with dolphins it is an even greater problem with billfish such as swordfish, which swim and accelerate faster than dolphins. In 2009, Taiwanese researchers from the National Chung Hsing University introduced new concepts of "kidnapped airfoils and circulating horsepower" to explain the swimming capabilities of swordfish. The researchers claim this analysis also "solves the perplexity of dolphin's Gray paradox". They also assert that swordfish "use sensitive rostrum/lateral-line sensors to detect upcoming/ambient water pressure and attain the best attack angle to capture the body lift power aided by the forward-biased dorsal fin to compensate for most of the water resistance power."
Billfish have prominent . Like tuna, mackerel and other scombroids, billfish streamline themselves by retracting their dorsal fins into a groove in their body when they swim. The shape, size, position and colour of the dorsal fin varies with the type of billfish, and can be a simple way to identify a billfish species. For example, the white marlin has a dorsal fin with a curved front edge and is covered with black spots. The huge dorsal fin, or sail of the sailfish is kept retracted most of the time. Sailfish raise them if they want to herd a school of small fish, and also after periods of high activity, presumably to cool down. Aquatic Life of the World pp. 332–333, Marshall Cavendish Corporation, 2000. .Dement J Species Spotlight: Atlantic Sailfish ( Istiophorus albicans) littoralsociety.org. Retrieved 1 April 2012.
Unlike coastal fish, billfish usually avoid inshore waters unless there is a deep dropoff close to the land. Instead, they swim along the edge of the continental shelf where cold nutrient rich upwellings can fuel large schools of forage fish. Billfish can be found here, cruising and feeding "above the craggy bottom like hawks soaring along a ridge line".
The boats cruise along the edge of the continental shelf where billfish can be found down to 200 metres (600 ft), sometimes near weed lines at the surface and submarine canyons and ridges deeper down. Commercial fishermen usually use drift nets or longlines to catch billfish, but recreational fishermen usually drift with bait fish or troll a bait or lure. Billfish are caught deeper down the water column by drifting with live bait fish such as ballyhoo, striped mullet or bonito. Alternatively, they can be caught by trolling at the surface with dead bait or Fishing lure designed to imitate bait fish.Williams RG and Nichols CR (2009) Encyclopedia of Marine Science Page 505, Infobase Publishing. .
Most recreational fishermen now tag and release billfish. A 2003 study surveyed 317,000 billfish known to have been tagged and released since 1954. Of these, 4122 were recovered. The study concluded that, while tag and release programs have limitations, they provided important information about billfish that cannot currently be obtained by other methods.
Billfish are primarily marketed in Japan, where they are eaten raw as sashimi. They are marketed fresh, frozen, canned, cooked and smoked. It is not usually a good idea to fry billfish. Swordfish and marlin are best grilled or broiled, or eaten raw as in sashimi. Sailfish and spearfish are somewhat tough and are better cooked over charcoal or smoked.Livingston AD (1996) Complete Fish & Game Cookbook Page 158, Stackpole Books. .
The stocks for individual species in billfish longline fisheries can "boom and bust" in linked and compensatory ways. For example, the Atlantic catch of blue marlin declined in the 1960s. This was accompanied by an increase in sailfish catch. The sailfish catch then declined from the end of the 1970s to the end of the 1980s, compensated by an increase in swordfish catch. As a result, overall billfish catches remained fairly stable.Duffy, J. Emmett (2008) Marine biodiversity and food security Encyclopedia of Earth. Updated 25 July 2008.
"Many of the world's fisheries operate in a data poor environment that precludes predictions about how different management actions will affect individual species and the ecosystem as a whole."Richardson DE (2008) "Physical and biological characteristics of billfish spawning habitat in the Straits of Florida" Open Access Dissertations. Paper 26. In recently years pop-up satellite archival tags have been used to monitor billfish. The capability of these tags to recover useful data is improving, and their use should result in more accurate stock assessments. In 2011, a group of researchers claimed they have, for the first time, standardized all available data about scombrids and billfishes so it is in a form suitable for assessing threats to these species. The synthesis shows that those species which combine a long life with a high economic value, such as the Atlantic blue marlin and the white marlin, are generally threatened. The combination puts such species in "double jeopardy".
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