Fish Facts » Swordfish
Description
The swordfish, as the only member of the family Xiphiidae, can be distinguished from other billfishes (Family Istiophoridae) by the shape of its prolonged "bill", which appears as a flattened oval in cross section. The bill is long relative to other billfishes and adults lack teeth in the jaws. While the young have scales, these are lost by the time the fish attain a body length of about 3 feet (1 m). Adults lack scales and teeth. The body is generally cylindrical. Two dorsal fins are present, although the second is quite small, separated from the first, and set far back on the body. The first dorsal fin is high and rigid. Likewise, there are two anal fins, although again the second is considerably smaller than the first. Pelvic fins are absent. The caudal fin is lunate, while the caudal peduncle has a pronounced keel on either side. The lateral line is also present in specimens up to 3 feet (1 m) in body length, but it too is lacking in adulthood. Prior to adulthood, swordfish morphology changes greatly, as described below. The color is blackish-brown above, fading to a lighter shade below. The fins are brown or dark brown.
Habitat
Generally an oceanic species, the swordfish is primarily a midwater fish at depths of 650-1970 feet (200-600 m) and water temperatures of 64 to 71°F (18-22°C). Although mainly a warm-water species, the swordfish has the widest temperature tolerance of any billfish, and can be found in waters from 41-80°F (5-27°C). The swordfish is commonly observed in surface waters, although it is believed to swim to depths of 2,100 feet (650 m) or greater, where the water temperature may be just above freezing. One adaptation which allows for swimming in such cold water is the presence of a "brain heater," a large bundle of tissue associated with one of the eye muscles, which insulates and warms the brain. Blood is supplied to the tissue through a specialized vascular heat exchanger, similar to the counter current exchange found in some tunas. This helps prevent rapid cooling and damage to the brain as a result of extreme vertical movements.
Diet
As opportunistic predators, swordfish feed at the surface as well as the bottom of their depth range (>2,100 ft (650 m)) as evidenced by stomach contents. They feed mostly upon pelagic fishes, and occasionally squids and other cephalopods. At lower depths they feed upon demersal fishes. The sword is apparently used in obtaining prey, as squid and cuttlefishes commonly exhibit slashes to the body when taken from swordfish stomachs. A recent study found the majority of large fish prey had been slashed, while small prey items had been consumed whole. Larval swordfish feed on zooplankton including other fish larvae. Juveniles eat squid, fishes, and pelagic crustaceans.
Fishery
Swordfish fisheries are active in tropical and temperate waters worldwide. The nations with the highest swordfish catches in the North Atlantic are Spain, the USA, Canada, Portugal, and Japan. Brazil, Japan, Spain, Taiwan, and Uruguay are the nations that catch the most swordfish in the South Atlantic. In 1995, the Atlantic swordfish industry caught 36,645 tons, or 41 percent of the world total catch of swordfish. Fisheries in the Atlantic primarily rely on longlines. In 1995, there were more than 1,900 active swordfish vessels in the US, most held by longlining vessels, although the fishery began as a harpooning industry. Canada has seen a significant increase in swordfish permits since their groundfish fisheries closed in the early 1990s. Mediterranean swordfish are now believed to form a separate stock from the Atlantic stocks, however they are not totally isolated. In 1995, the Mediterranean catch accounted for 9 percent of the world total. In the Indian Ocean, swordfish concentrations occur off the coasts of India, Sri Lanka, Saudi Arabia, and eastern Africa. While the Indian fishery was traditionally largest in the eastern Indian Ocean, it has not been productive in recent years. The western Indian Ocean now dominates the regional catch, which amounted to 15 percent of the world total catch in 1995. Almost half the worldwide catch of swordfish occurs in the Pacific. The Pacific swordfish fishery is active in five areas: the northwestern Pacific, off southeastern Australia, off northern New Zealand, the southeastern tropical Pacific, and off Baja California, Mexico. As demand in North America and Europe increases and stricter quotas are set in the Atlantic, scientists expect Pacific swordfish will face more intense fishing pressure in coming years.
Size
Swordfish reach a maximum size of 177 in. (455 cm) total length and a maximum weight of 1,400 lbs. (650 kg), although the individuals commercially taken are usually 47 to 75 in. (120-190 cm) long in the Pacific. Females are larger than males of the same age, and nearly all specimens over 300 lbs. (140 kg) are female. Pacific swordfish grow to be the largest, while western Atlantic adults grow to 700 lbs. (320 kg) and Mediterranean adults are rarely over 500 lbs. (230 kg). The IGFA all tackle record is 1182 lb. (536.15 kg).