Swordfish
| Swordfish Temporal range: 33.9–0 Ma Early Oligocene to Present[1] | |
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| Conservation status | |
| Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Actinopterygii |
| Subclass: | Neopterygii |
| Infraclass: | Teleostei |
| Order: | Perciformes |
| Family: | Xiphiidae |
| Genus: | Xiphias Linnaeus, 1758 |
| Species: | X. gladius |
| Binomial name | |
| Xiphias gladius Linnaeus, 1758 | |
They are the sole member of their family Xiphiidae.[5]
Physiology
The swordfish is named after its bill resembling a sword (Latin gladius).[4] This makes it superficially similar to other billfish such as marlin, but upon examination their physiology is quite different and they are members of different families.[6]They commonly reach 3 m (9.8 ft) in length, and the maximum reported is 4.55 m (14.9 ft) in length and 650 kg (1,400 lb) in weight.[3][4] The International Game Fish Association's all-tackle angling record for a swordfish was a 1,182 lb (536 kg) specimen taken off Chile in 1953.[2] Females are larger than males, and Pacific swordfish reach a greater size than northwest Atlantic and Mediterranean swordfish.[4] They reach maturity at 4–5 years of age and the maximum age is believed to be at least 9 years.[4]
Swordfish are ectothermic animals; however, swordfish, along with some species of shark, have special organs next to their eyes to heat their eyes and brain. Temperatures of 10 to 15 °C above the surrounding water temperature have been measured. The heating of the eyes greatly improves their vision, and consequently improves their ability to catch prey.[7][8] Out of the 25,000+ fish species, only 22 are known to have a mechanism to produce heat. These include the swordfish, marlin, tuna and some sharks.[7][8]
Behavior and ecology
Swordfish prefer water temperatures between 18 °C (64 °F) and 22 °C (72 °F),[2] but have the widest tolerance among billfish and can be found from 5 °C (41 °F) to 27 °C (81 °F).[4] This highly migratory species typically moves towards colder regions to feed during the summer.[4] Swordfish feed daily, most often at night when they rise to surface and near-surface waters in search of smaller fish. During the day they commonly occur to depths of 550 m (1,800 ft) and have exceptionally been recorded as deep as 2,878 m (9,442 ft).[2] Adults feed on a wide range of pelagic fish such as mackerel, barracudinas, silver hake, rockfish, herring and lanternfishes, but they also take demersal fish, squid and crustaceans.[3][4] In the northwestern Atlantic, a survey based on the stomach content of 168 individuals found that 82% had eaten squid and 53% had eaten fish, including gadids, scombrids, butterfish, bluefish and sand lance.[10] Large prey-items are typically slashed with the sword, while small are swallowed whole.[4]
Swordfish are not schooling fish. They swim alone or in very loose aggregations, separated by as much as 10 m (33 ft) from a neighboring swordfish. They are frequently found basking at the surface, airing their first dorsal fin. Boaters report this to be a beautiful sight, as is the powerful jumping for which the species is known. This jumping, also called breaching, is thought by some researchers to be an effort to dislodge pests, such as remora or lampreys.[citation needed] Almost 50 species of parasites have been documented in swordfish. In addition to remoras, lampreys and cookiecutter shark, this includes a wide range of invertebrates such as tapeworms, roundworms and copepods.[4]
Except for humans, fully adult swordfish have few enemies. Among marine mammals, at least killer whales sometimes prey on adult swordfish.[4] The shortfin mako, an exceptionally fast species of shark, sometimes take swordfish.[11] Dead or dying shortfin makos have been found with broken off swords in their head, revealing the potential danger of this type of prey.[11] Juvenile swordfish are far more vulnerable to predation and are eaten by a wide range of predatory fish.[4]
Reproduction
In the North Pacific, batch spawning mainly occurs in water warmer than 24 °C (75 °F) during the spring and summer, and year round in the equatorial Pacific.[2] In the north Atlantic spawing is known from the Sargasso Sea,[3] and in water warmer than 23 °C (73 °F) and less than 75 m (246 ft) deep.[2] Spawning occurs from November to February in temperatures above 20 °C (68 °F) in the south Atlantic off south Brazil.[3] Spawning is year-round in the Caribbean Sea and other warm regions of the west Atlantic.[4]Large females can carry more eggs than small females, and between 1 million to 29 million eggs have been recorded.[2] The pelagic eggs measure 1.6–1.8 mm (0.063–0.071 in) in diameter and 2 ½ days after fertilization the embryonic development occurs.[3][4] The surface-living and unique-looking larvae are 4 mm (0.16 in) long at hatching.[3][4] The bill is evident when the larvae reach 1 cm (0.39 in) in length.[3]
Fisheries
Swordfish have been fished widely since ancient times, among others in the sea between Sicily and Calabria, such as off the Tyrrhenian coast in the Reggio province. It is a typical dish in the cuisine of this region.[13]
Swordfish were harvested by a variety of methods at small scale (notably harpoon fishing) until the global expansion of long-line fishing.
Swordfish are vigorous, powerful fighters. When hooked or harpooned, they have been known to dive so quickly that they have impaled their swords into the ocean bottom up to their eyes. Although there are no reports of unprovoked attacks on humans, swordfish can be very dangerous when harpooned. They have run their swords through the planking of small boats when hurt.
Recreational fishing
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There are various ways to fish for swordfish, but the most common method is deep-sea fishing. Because many swordfish used to be caught by long-lining near shore, the remaining population of swordfish live about 40 mi (64 km) or more off the coast. The boat is allowed to drift, as the ocean bottom is too deep for anchors. Swordfishing requires a specialized, strengthened fishing rod as swordfish are quite large. Standard bait is large chunks of mackerel, herring, mullet, bonito or squid; one can also use live bait. Imitation squids and other imitation fish lures can also be used, and specialized lures made specifically for sword fishing using plastic glow sticks are also used.
As food
The flesh of some swordfish can acquire an orange tint, reportedly from their diet of shrimp or other prey. Such fish are sold as "pumpkin swordfish," and command a premium over their whitish counterparts. (Information from U.S. vendor Whole Foods.)
Swordfish is a particularly popular fish for cooking. Since swordfish are large animals, meat is usually sold as steaks, which are often grilled. Swordfish meat is relatively firm, and can be cooked in ways more fragile types of fish cannot (such as over a grill on skewers). The color of the flesh varies by diet, with fish caught on the east coast of North America often being rosier.
There is some controversy over the kashrut status of swordfish, because adult fish lose their scales (sea life must have scales and fins to be considered kosher.) The Tzitz Eliezer 9:40 says they are forbidden, while Rabbi [Schachter] maintains that swordfish is kosher, because the Torah does not specify what the scales have to look like.
Conservation status
In 1998, the United States Natural Resources Defense Council and SeaWeb hired Fenton Communications to conduct an advertising campaign to promote their assertion that the swordfish population was in danger due to its popularity as a restaurant entree.[17]
The resulting "Give Swordfish a Break" promotion was wildly successful, with 750 prominent U.S. chefs agreeing to remove North Atlantic swordfish from their menus, and also persuaded many supermarkets and consumers across the country.
The advertising campaign was repeated by the national media in hundreds of print and broadcast stories, as well as extensive regional coverage. It earned the Silver Anvil award from the Public Relations Society of America as well as Time magazine's award for the top five environmental stories of 1998.
Subsequently, the US National Marine Fisheries Service proposed a swordfish protection plan that incorporated the campaign's policy suggestions. Then-US President Bill Clinton called for a ban on the sale and import of swordfish and in a landmark decision by the federal government, 132,670 sq mi (343,600 km²) of the Atlantic ocean were placed off-limits to fishing as recommended by the sponsors.
In the North Atlantic, the swordfish stock is fully rebuilt, with biomass estimates currently 5% above the target level.[18] There are no robust stock assessments for swordfish in the northwestern Pacific or South Atlantic, and there is a paucity of data concerning stock status in these regions. These stocks are considered unknown and a moderate conservation concern. The southwestern Pacific stock is a moderate concern due to model uncertainty, increasing catches, and declining CPUEs (catch per unit effort). Overfishing is likely occurring in the Indian Ocean, and fishing mortality exceeds the maximum recommended level in the Mediterranean, thus these stocks are considered of high conservation concern.[19]
In 2010, Greenpeace International has added the swordfish to its seafood red list. "The Greenpeace International seafood red list is 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."[20]
- Article Source: http://en.wikipedia.org/
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