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Swordfish
Swordfish , also known as Broadbill in some countries, are large, highly migratory, predatory fish characterized by a long, flat bill. They are a popular sport fish of the billfish category, though elusive. Swordfish are elongated, round-bodied, and lose all teeth and scales by adulthood. They reach a maximum size of 177 in. and 1,400 lb . The International Game Fish Association's all-tackle angling record for a swordfish was a 1,182 lb specimen taken off Chile in 1953.
They are the sole member of their family Xiphiidae.
Physiology
The swordfish is named after its sharp beak resembling a sword (Latin gladius), which together with its streamlined physique allows it to cut through the water with great ease and agility. Contrary to belief the "sword" is not used to spear, but instead may be used to slash at its prey in order to injure the prey animal, to make for an easier catch. Mainly the swordfish relies on its great speed, capable of reaching speeds up to 50 mph , and agility in the water to catch its prey. One possible defensive use for the sword-like bill is 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, but they don't always win. Sometimes in the struggle with a shark a swordfish can kill it by ramming it in the gills or belly.
Like most fish, the females grow larger than the males, with males over 300 lb being rare. Females mature at 45 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 24C 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, forage fish as well as benthic species of hake and rockfish. Squid are important when available. Swordfish are thought to 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 consequently 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, and tuna.
Swordfish are not schooling fish. They swim alone or in very loose aggregations, separated by as much as 10 meters 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. It could also be a way of surface feeding by stunning small fish as they jump out of the water, making the fish more easily captured for food.
Swordfish feed daily, most often at night when they rise to surface and near-surface waters in search of smaller fish. They have been observed moving through schools of fish, thrashing their swords to kill or stun their prey and then quickly turning to consume their catch. In the western North Atlantic, squid is the most popular food item consumed. But fish, such as menhaden, mackerel, bluefish, silver hake, butterfish, and herring also contribute to the swordfish diet.
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.
The adults have few natural enemies, with the exception of large sharks, sperm whales, and orcas. They are easily frightened by small boats, yet paradoxically, large craft are often able to draw very near without scaring them. This makes swordfish easy to harpoon.
The swordfish is often mistaken for other billfish (like marlin), but upon examination their physiology is quite different.
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 1.61.8 mm in diameter. Embryonic development occurs during the 2 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, the 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 , the bill is notably elongated, 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 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 , the second dorsal fin has developed, and at approximately 60 inches , only the large lobe remains of the first dorsal fin.
Harvest
Swordfish were harvested by a variety of methods at small scale (notably harpoon fishing) until the global expansion of long-line fishing.
Longline gear can be targeted to a variety of fish, but bycatch remains a significant problem.
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.
Swordfish are classified as oily fish. Many sources including the United States Food and Drug Administration warn about potential toxicity from high levels of methylmercury in swordfish. 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.
(See mercury in fish for more details.)
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.")
Conservation status
Swordfish are not listed as an endangered species.
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.
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, of the Atlantic ocean were placed off-limits to fishing as recommended by the sponsors.
In the North Atlantic, the swordfish stock is nearly rebuilt,
but biomass remains slightly below that at which maximum sustainable yield is produced, and abundance is increasing.
This stock is considered a moderate conservation concern until the stock is fully rebuilt. 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.
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."
Recreational importance
Recreational fishing has developed a sub-specialty called sword fishing. It has become quite popular throughout many parts of the world. Because there is a ban on Long lining along many parts of seashore, swordfish populations are showing signs of recovery from the overfishing caused by Long lining along the coast. The population recovery is far from complete and the swordfish population is still at a much lower level than it once was.
There are various different ways to fish for swordfish, but the most common and popular method seems to be deep sea fishing. Because many swordfish used to be caught by long lining near shore, the remaining population of swordfish lives about 40 miles or more off the coast of most locations, and as such is only accessible by boat. Standard practice usually to let the boat being fished off of to drift, as the ocean bottom is too deep for any conventional fishing boat to anchor as the bottom is often thousands of feet deep. It requires a specialized, strengthened fishing rod as swordfish are extremely large fish. Standard bait that is used to attract the fish would be either large chunks of mackerel, herring, mullet, bonito or squid, and if the bait is small enough then the fisherman can 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.
One of the most used method to catch sword fish is trolling. Fisherman cast their lines and then wait until a fish hits the line. Swordfish will often not suddenly hit and take the bait as they have soft mouths. The ensuing fight after a bite can take several hours to complete, as the fish can weigh several hundred pounds and is very strong.
Swordfish is not often sought for its meat by private fishing charters, but for the recreational aspect of the chase and fight that is involved with the fish. Most fishermen and captains of charters practice capture-and-release fishing, as they are a rare fish.
References
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, 5558
FDA Consumer:Mercury In Fish:Cause For Concern?
External links
Swordfish, Florida Museum of Natural History
Swordfish, Seafood Watch, Monterey Bay Aquarium
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This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article Swordfish
