Swordfish

Xiphias gladius family Xiphiidae taxonomy

Xiphias gladius Linnaeus, 1758, European seas.

other common names French: Espadon; Spanish: Pez espada.

physical characteristics

Reaches a maximum size of 175 in (445 cm) total length and approximately 1,190 lb (540 kg). The body is elongate and cylindrical. Two widely separated dorsal fins in adults, the first much larger than the second, the first with 34-49 rays, the second with four to six rays. Two separate anal fins in adults, the first with 12-16 rays, the second with three or four rays. Pectoral fins falcate, located low on body sides, with 17-19 rays. Caudal fin large and lunate, with a deep notch on upper and lower profiles of caudal peduncle. Fine file-like teeth and scales with small spines are present in juveniles but become embedded in the skin with growth at approximately 3 ft (1 m) in length. Left and right branchiostegal membranes separated distally. Vertebrae, 26. Back and sides of body blackish brown, gradually fading to light brown on ventral side.

distribution

Cosmopolitan in tropical, temperate, and sometimes cold waters of all oceans, including the Mediterranean, Black, and Caribbean seas.

habitat

This is an epipelagic and mesopelagic, oceanic species, usually found in surface waters warmer than 55.4°F (13°C), the optimum temperature range being 64.4-71.6°F (18-22°C). Sword-fishes have been acoustically tracked and directly observed from submersibles in the western Atlantic and eastern Pacific to depths of 2,024 ft (617 m).

behavior

It is likely that swordfishes use the sword to stun or kill some prey, as shown by slashes on the bodies of squid and fishes found in swordfish stomachs. The brain and eyes of swordfish are warmer than the water in which they live. The tissue that heats the brain is developed from the superior rectus muscle of the eye. The brain heater protects the central nervous system from rapid cooling during vertical excursions of as much as 984 ft (300 m) that these fish may make through a temperature range as great as 34.2°F (19°C) in 2 hours.

feeding ecology and diet

Adult swordfishes are opportunistic feeders, known to forage for their food from the surface to the bottom over a wide depth range. Over deep water, they feed primarily on pelagic fishes including tuna, dolphinfishes, lancetfishes, flyingfishes, and pelagic squids. In shallow waters swordfishes often take neritic pelagic fishes such as mackerel, herring, anchovies, sardines, and sauries. Large adults may make feeding trips to the bottom for demersal fishes.

reproductive biology

In the western Atlantic, spawning apparently occurs throughout the year in the Caribbean, the Gulf of Mexico, and waters off Florida. Swordfishes spawn in the upper water layers at depths of 0-246 ft (0-75 m) and temperatures of approximately 73.4°F (23°C). Swordfishes first spawn at 5 or 6 years of age and 59-67 in (150-170 cm) eye-fork length and lay 2-5 million eggs.

conservation status

Listed by IUCN as Data Deficient. Populations of swordfish have been greatly reduced by fishing, particularly in the Atlantic Ocean. A consumer boycott of Atlantic swordfish organized by the United States-based Natural Resources Defense Council and Sea Web affected prices enough to gather crucial momentum toward a recovery plan for depleted swordfish in the Atlantic (Safina, 2001).

significance to humans

Appreciation of swordfish as a food fish is recent. Swordfishes brought only approximately $0.24 per pound (0.5 kg) in 1919 and $0.60 in 1946. There are important fisheries for swordfish in all three major oceans. Swordfishes are caught by long line, harpoon, drift gill net, set nets, and other fishing gear. FAO catch statistics for 1991-2000 show catches of 76-116 thousand tons (69-105 thousand metric tons) per year by 77 countries. Restrictions on the sale of swordfish containing levels of mercury greater than 0.5 ppm in Canada and the United States in the early 1970s caused collapse of the Canadian fishery and severely restricted landings in the United States. The mercury guidelines were raised to 1.0 ppm in 1979, and by 1980 catch and effort had reached a new high in the northwest Atlantic. Swordfishes are important sport fishes. The all-tackle game fish record is a 1,182-lb (536.2-kg) fish taken off Chile. ♦

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