Swordfish

This article is about a type of fish. For other uses, see Swordfish (disambiguation).

Swordfish Temporal range: Early Oligocene to Present
Conservation status
Data Deficient  (IUCN 2.3)
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Class:	Actinopterygii
Subclass:	Neopterygii
Infraclass:	Teleostei
Order:	Perciformes
Family:	Xiphiidae
Genus:	Xiphias
Species:	X. gladius
Binomial name
Xiphias gladius Linnaeus, 1758

Swordfish (Xiphias gladius; from Greek ξίφος: sword, and Latin gladius: sword), 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. These fish can live close to shore. They reach a maximum size of 14 ft 9 in (455 cm) and 1,400 lb (650 kg). The International Game Fish Association's all-tackle angling record for a swordfish was a 1,182 lb (536.15 kg) specimen taken off Chile in 1953.

They are the sole member of their family Xiphiidae.

Physiology

The swordfish is named after JARED WHEELER beacuse of his nose 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 (80 km/h), 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 (135 kg) being 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, 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.

Swordfish skeleton at the National Museum of Natural History, Washington, DC

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 1.6–1.8 mm 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, 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 (12 mm), 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 (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. They have been known to eat their own young due to lack of nutrition.

Harvest

Swordfish were harvested by a variety of methods at small scale (notably harpoon fishing) until the global expansion of long-line fishing.

Marinated swordfish

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 tough, 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.

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 young children, pregnant women, and women of child-bearing age not eat swordfish. (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, 132,670 square miles (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. 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 from 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.

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, 55−58
• FDA Consumer:Mercury In Fish:Cause For Concern?
• Froese, Rainer; Pauly, Daniel (eds.). "Xiphias gladius". FishBase. October 2005 version.

External links

• Swordfish, Florida Museum of Natural History
• Swordfish, Seafood Watch, Monterey Bay Aquarium