Swordfish - Behavior and Ecology

Behavior and Ecology

Contrary to popular 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 and agility in the water to catch its prey. It is undoubtedly among the fastest fish, but the basis for the frequently quoted speed of 60 mph (97 km/h) is unreliable.

Swordfish prefer water temperatures between 18 °C (64 °F) and 22 °C (72 °F), but have the widest tolerance among billfish and can be found from 5 °C (41 °F) to 27 °C (81 °F). This highly migratory species typically moves towards colder regions to feed during the summer. Swordfish feed daily, most often at night when they rise to surface and near-surface waters in search of smaller fish. During the day they commonly occur to depths of 550 m (1,800 ft) and have exceptionally been recorded as deep as 2,878 m (9,442 ft). Adults feed on a wide range of pelagic fish such as mackerel, barracudinas, silver hake, rockfish, herring and lanternfishes, but they also take demersal fish, squid and crustaceans. In the northwestern Atlantic, a survey based on the stomach content of 168 individuals found that 82% had eaten squid and 53% had eaten fish, including gadids, scombrids, butterfish, bluefish and sand lance. Large prey-items are typically slashed with the sword, while small are swallowed whole.

Swordfish are not schooling fish. They swim alone or in very loose aggregations, separated by as much as 10 m (33 ft) 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. Almost 50 species of parasites have been documented in swordfish. In addition to remoras, lampreys and cookiecutter shark, this includes a wide range of invertebrates such as tapeworms, roundworms and copepods.

Except for humans, fully adult swordfish have few enemies. Among marine mammals, at least killer whales sometimes prey on adult swordfish. The shortfin mako, an exceptionally fast species of shark, sometimes take swordfish. Dead or dying shortfin makos have been found with broken off swords in their head, revealing the potential danger of this type of prey. Juvenile swordfish are far more vulnerable to predation and are eaten by a wide range of predatory fish.