Swordfish

By : Malia Schwartz, Deborah Grossman-Garber, and Henry Milliken

The swordfish (Xiphias gladius Linnaeus 1758), also called the broadbill, is the only member of the family Xiphiidae. As its name implies, this magnificent fish is characterized by an upper jaw that extends to form a flat, sharp-edged "sword." Swordfish are impressive jumpers and powerful fighters—thrilling for anglers and boaters alike.

Physical Characteristics

The swordfish has a stout, fairly rounded body and large eyes. The first dorsal fin (rising from the back of the fish) is tall and crescent-shaped. The second dorsal fin is quite separate from the first and very small. Both are soft-rayed—having thin, bony rods that extend from the base of the fin and support the fin membrane. The anal fins approximate the shape of the dorsal fins, but are noticeably smaller. Ventral fins, found on the underside of fish, are absent. There is a strong, longitudinal keel, or ridge, on either side of the caudal peduncle (the base of the tail where the tail fins project from), which leads to a broad, crescent-shaped tail. Adult swordfish have neither teeth nor scales.

The swordfish snout elongates into a true sword shape. Measuring at least one-third the length of the body, it is long, flat, pointed, and very sharp. The lower jaw is much smaller, though just as pointed, ending in a very wide mouth.

The bodies of swordfish fry (recently hatched fish larvae) are quite different form those of the adults. Their upper and lower jaws are equally prolonged; bodies are long, thin, and snakelike; they are covered with rough, spiny scales and plates; tails are rounded; and they have just one long dorsal and anal fin.

Swordfish coloration varies greatly among individuals. The dorsal side can range from dark brown to grayish-blue. This dark shading can extend anywhere from halfway down the side to almost the full extent of the body. The remaining area of the skin is tinged silvery white.

In Northeast waters, only the spearfish bears any resemblance to the swordfish. It is distinguished from the swordfish by its rounded sword, small teeth, a long, continuous dorsal fin, and ventral fins.

Size

Swordfish are very large fish. Today, the average fish caught in the commercial fishery weighs between 90 and 150 kilograms (1 kilogram equals 2.2 pounds). While fish over 200 kg are unusual, the largest recorded in the North Atlantic ocean weighed 550 kg. The largest fish to be caught on a tackle weighed 274 kg. These larger fish measure approximately 4.5 meters in length (1 meter equals 3.3 feet)—with a 3 meter body and a 5 meter sword.

Female swordfish grow faster, live longer, and are proportionally heavier than their male counterparts. Research shows that by 1 year of age, the female is already almost 4 kg. During the next 2 years, she triples her weight of the previous year. By age 4, the female is likely to weigh 70 kg, and at age 5, 110 kg. Similar data for males and older swordfish are inconclusive.

Longevity

Swordfish reach sexual maturity at about 2 to 3 years of age, and live for at least nine years. While they may survive longer, no such documentation exists. The majority of swordfish caught in the North Atlantic sport fishery are thought to be 4 to 5 years old.

Distribution

Swordfish are pelagic fish—living within the water column rather than on the bottom or in coastal areas. They are typically found at depths of between 180 meters and 580 meters, and are found worldwide in temperate and tropical waters. They are believed to prefer waters where the surface temperature is above 15°C (58°F), although they can tolerate temperatures as low as 10°C (50°F). There seems to be some correlation between larger size and the ability to tolerate colder temperatures. Few fish under 90 kg are found in waters less than 18°C (64°F).

Swordfish are summer and fall visitors to New England waters, entering the warming Atlantic coastal waters from far offshore in the Gulf Stream around June and departing in late October. Evidence suggests that such onshore-offshore seasonal migrations are more prevalent than are migrations between the northern feeding areas off Cape Hatteras and the southern spawning grounds off Florid and the Caribbean.

Behavior

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 remoras 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 and sperm and killer whales. 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.

Fisheries

Today, swordfish are caught in gill nets, with harpoons, and, most successfully, on longlines consisting of a main line, usually several miles long, which is supported in the water column by floats and from which baited hooks are suspended. In addition, swordfish are often an incidental catch in the tuna fishery.

The sport fishery normally fishes for swordfish by trolling and drift-fishing, using rod-and-reel gear. The catch rate has increased considerably since fishermen began in the mid-1970s to fish for swordfish at night using drifting baited lines.

Once almost unsalable, swordfish meat gained in popularity during World War II and continued through the early 1970s. In 1971, the U.S. and Canadian swordfish fishery was essentially terminated following U.S. Food and Drug Administration (FDA) restrictions imposed on the sale of swordfish found to have levels of mercury in the flesh higher than 0.5 parts per million (ppm).

But gradually, the U.S. fishery began to rebound. In 1979, the FDA raised the acceptable mercury level to 1.0 ppm, based, in part, on a National Marine Fisheries Service study, showing that a 1.0 ppm action level would adequately protect consumers. Finally, in 1984, the FDA switched from enforcing the mercury action level based on total mercury concentration to methyl mercury concentration. This change occurred for two reasons: (1) It was determined that methyl mercury was the toxic component of the total mercury concentration, and (2) a test specific for methyl mercury became available. Since then, both catch and fishing effort have been exceedingly high in the Atlantic Ocean, with swordfish meat commanding top prices in the marketplace.

While swordfish sold on commercial markets is closely monitored to make sure that methyl mercury levels remain below the 1.0 ppm action level, most experts urge those concerned about chemical contaminants to take certain precautions:

1. Eat a variety of different fish; don’t restrict yourself to swordfish.
2. Avoid eating excessive amounts of any single type of fish.
3. Avoid eating the internal organs of the fish—they typically contain higher contaminant concentrations than the flesh.
4. When catching your own swordfish, check and follow all applicable health advisories.
5. High-risk individuals—pregnant women, women of childbearing age, and children under age 15—should limit their consumption of swordfish. Pregnanat or nursing mothers should limit their consumption to once a month.
6. If you choose to eat a sport-caught swordfish that may contain elevated levels of contaminants, trim away fatty areas and use cooking methods like baking or broiling, to allow fats and juices to drain away.