The swordfish (Xiphias gladius) is one of the largest of the billfishes -- big, active marine predators characterized by spear-like snouts. Though it superficially resembles marlins and sailfishes, the swordfish, also called the broadbill, belongs to its own family, Xiphiidae. One of the ocean's most impressive beasts, the swordfish supports major commercial fisheries in the Atlantic, Indian and Pacific Oceans.
The swordfish’s common name reflects its most distinguishing feature: the long, flattened bill. The swordfish lacks some key features possessed by marlins and sailfishes: namely, teeth, scales and pelvic fins. Besides the formidable snout, the fish’s most striking characteristics are its tall, stiff first dorsal fin and the great “lunate," or crescent-moon-shaped, tail. Mature swordfishes rank among the heavyweights of bony fish: Females, the bigger sex, may attain lengths of 4.6 meters (15 feet) and weights of 650 kilograms (1,400 pounds). Black or brownish gray on top, the swordfish’s hide grades to a light-gray belly. This “countershading” pattern, common among open-ocean fishes, helps the animal camouflage itself against sunlit waters above and black depths below.
Range and Habitat
Swordfish, the most cold tolerant of the billfishes, range widely in the world ocean, found from tropical to cold waters mainly between 60 degrees N and 45 degrees S in latitude. Four distinct stocks exist in the Pacific; three in the Atlantic, including a heavily fished population in the Mediterranean; and one in the Indian Ocean. In summer, swordfish migrate into colder waters to feed, then return to warmer seas in winter. In the equatorial zone, they spawn throughout the year; in colder latitudes, breeding occurs in spring and summer. The fish forage widely within the water column, from surface waters to depths down to at least 650 meters (2,100 feet).
Swordfish Feeding Habits
Swordfish rest near the top of the marine food chain. Beginning with a larval diet of zooplankton, the animal transitions to feeding on squid, small fish and crustaceans as it grows larger. Adult swordfish primarily eat fish such as mackerel, herring, bluefish and barracudinas, as well as cephalopods, especially squid. Slash wounds observed on larger prey exhumed from swordfish stomachs suggest the predators sometimes use their bills to kill or disable victims.
A Mortal Enemy
Given their size and strength, adult swordfish don't have much to fear. Nonetheless, a scarce few marine hunters are formidable enough to occasionally prey on them. Most notable is the shortfin mako shark, which -- as an athletic, 50-kilometer-per-hour (31-mile-per-hour) swimmer -- can match the swordfish’s speed stroke for stroke. A 330-kilogram (730-pound) mako landed in the Bahamas yielded a 55-kilogram (120-pound) swordfish -- swallowed whole -- from its stomach. Such predation is risky for the shark; makos scarred by swordfish bills are often observed. Meanwhile, the lesser-known longfin mako, slower than its shortfin relative, likely doesn’t have the capability to catch a healthy swordfish, although one longfin was caught with a shard of swordfish spear lodged in its abdomen. As the ReefQuest Centre for Shark Research notes, it’s possible in this case that the longfin collided with the billfish while both were feeding on the same school of fish or squid. Great white sharks and orcas may also pose an occasional threat to swordfish.
The Commercial Swordfish Industry
Swordfish are a food source of major economic importance in many countries, from the United States to Chile to Japan. They may be harpooned, gill-netted or snagged by longline, including as bycatch in tuna operations. According to Monterey Bay Aquarium’s 2011 “Seafood Watch” assessment, the swordfish stocks of most concern in terms of overfishing are those in the Mediterranean and Indian Ocean.