Swordfish
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For other uses, see Swordfish (disambiguation).
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| Xiphias gladius Linnaeus, 1758 |
Swordfish (Xiphias gladius) are large, highly migratory, predatory fish characterized by a long, flat bill in contrast to the smooth, round bill of the marlins. They are a popular sport fish, though elusive. Swordfish are elongated, round-bodied, and lose all teeth and scales by adulthood. They reach a maximum size of 14 ft (4.3 m) and 1,190 lb (540 kg). 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.
They are the sole member of their family Xiphiidae.
The swordfish is known as The Gladiator (gladius) because of the sharp, sword-like bill it wields as a weapon—to spear prey as well as for protection from its few natural predators. The shortfin mako shark is one of the rare sea creatures big enough and fast enough to chase down and kill an adult swordfish.
Swordfish are distributed throughout the world's marine ecosystem, in tropical, subtropical and temperate waters, between approximately 45° north and 45° south[2]. They tend to concentrate where major ocean currents meet, and along temperature fronts. They inhabit the mixed surface waters where temperatures are greater than 15 °C but also can move and hunt in water as cool as 5 °C for short periods aided by specially adapted heat exchange organs which are able to increase the temperature of their brain and eyes by 10–15 °C.
Areas of greater apparent abundance occur north of Hawaii along the North Pacific transition zone, along the west coasts of the U.S. and Mexico and in the western Pacific, east of Japan. Migration patterns have not been described although tag release and recapture data indicate an eastward movement from the central Pacific, north of Hawaii, toward the U.S. West Coast. Acoustic tracking indicates some diel movement from deeper depths during the daytime and moving into the mixed surface water at night. At times they appear to follow the deep scattering layer, and small prey, as they undertake these vertical movements.
Females grow larger than males, as males over 300 lb (135 kg) are rare. Females mature at 4-5 years of age in northwest Pacific while males mature first at about 3 to 4 years. In the North Pacific, batch spawning occurs in water warmer than 24 °C from March to July and year round in the equatorial Pacific. Adult swordfish forage includes pelagic fish including small tuna, dorado, barracuda, flying fish, mackerel, as well as benthic species of hake and rockfish. Squid are important when available. Swordfish likely have few predators as adults although juveniles are vulnerable to predation by large pelagic fish.
While swordfish are cold-blooded animals, they have special organs next to their eyes to heat their eyes and also their brain. Temperatures of 10 to 15 C° above the surrounding water temperature have been measured. The heating of the eyes greatly improves the vision, and subsequently improves their ability to catch prey. Out of the 25 000+ species of bony fish, only about 22 are known to have the ability to heat selected body parts above the temperature of the surrounding water. These include the swordfish, marlin, tuna and some sharks.
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[edit] Reproduction
Swordfish have been observed spawning in the Atlantic Ocean, in water less than 250 ft. (75 m) deep. Estimates vary considerably, but females may carry from 1 million to 29 million eggs in their gonads. Solitary males and females appear to pair up during the spawning season. Spawning occurs year-round in the Caribbean Sea, Gulf of Mexico, the Florida coast and other warm equatorial waters, while it occurs in the spring and summer in cooler regions. The most recognized spawning site is in the Mediterranean, off the coast of Italy. The height of this well-known spawning season is in July and August, when males are often observed chasing females. The pelagic eggs are buoyant, measuring 1.6-1.8mm in diameter. Embryonic development occurs during the 2 ½ days following fertilization. As the only member of its family, the swordfish has unique-looking larvae. The pelagic larvae are 4 mm long at hatching and live near the surface. At this stage, body is only lightly pigmented. The snout is relatively short and the body has many distinct, prickly scales. With growth, the body narrows. By the time the larvae reach half an inch long (12 mm), the bill is notably elongate, but both the upper and lower portions are equal in length. The dorsal fin runs the length of the body. As growth continues, the upper portion of the bill grows proportionately faster than the lower bill, eventually producing the characteristic prolonged upper bill. Specimens up to approximately 9 inches (23 cm) in length have a dorsal fin that extends the entire length of the body. With further growth, the fin develops a single large lobe, followed by a short portion that still reaches to the caudal peduncle. By approximately 20 inches (52 cm), the second dorsal fin has developed, and at approximately 60 inches (150 cm), only the large lobe remains of the first dorsal fin.
[edit] Swordfish in cooking
Swordfish is a particularly popular fish for cooking. Since swordfish are large animals, meat is usually sold as steaks, which are often grilled. The color of the flesh varies by diet, with fish caught on the east coast of North America often being rosier.
However, many sources including the United States Food and Drug Administration warn about potential toxicity from high levels of methylmercury in swordfish[3]. The FDA recommends that women who are pregnant or who may become pregnant should eat no more than one seven-ounce serving a month; others should eat no more than one serving a week.
[edit] Swordfish Endangered
Due to commercial fishing, the average swordfish has dropped from 260 pounds in 1960 to 90 pounds in 1996[4]. The numbers of North Atlantic swordfish have dropped to less than 50% of what they were just 20 years ago and U.S. commercial fisherman account for about a third of the worldwide catch. This alarming decline is largely due to the popularity of this species by seafood lovers. A major part of the problem is related to over-fishing, general absence of regulations regarding fish harvest during critical periods, no minimum fish size, and lack of protection for spawning and nursery areas.[5] This fish has been included on many endangered fish lists including the Audubon Society and others.
[edit] References
- ^ Safina (1996). Xiphias gladius. 2006 IUCN Red List of Threatened Species. IUCN 2006. Retrieved on 12 May 2006.
- ^ Ibáñez, C. et al. (2004). Diet of the swordfish Xiphias gladius Linnaeus, 1758 in oceanic waters off central Chile in winter 2003 (abstract in English, text in Spanish). Investigaciones marinas 32 (2).
- ^ [1] "What you need to know about mercury in fish and shellfish."
- ^ [2] "Lines of Death: Longlining and bycatch."
- ^ Clover, Charles. 2004. The End of the Line: How overfishing is changing the world and what we eat. Ebury Press, London. ISBN 0-09-189780-7
- Michael Hopkin (2005): Swordfish heat their eyes for better vision. Nature, 10 January 2005
- Fritsches, Kerstin A., Brill, Richard W., and Warrant, Eric J. (2005): Warm Eyes Provide Superior Vision in Swordfishes. Current Biology 15, 55−58
- FDA Consumer:Mercury In Fish:Cause For Concern?
- "Xiphias gladius". FishBase. Ed. Ranier Froese and Daniel Pauly. 10 2005 version. N.p.: FishBase, 2005.
