Malia Schwartz, Deborah Grossman-Garber, and Henry Milliken
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 fightersthrilling for anglers and boaters alike.
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-rayedhaving
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.
Other billfish, including marlins, inhabit Northeast waters, but only the
spearfish bears a strong resemblance to the swordfish. It is distinguished
from the swordfish by its rounded sword, small teeth, a long, continuous
dorsal fin, and ventral fins.
While the largest swordfish recorded in the North Atlantic ocean weighed
fish over 200
kg are unusual. Today, the average fish caught in the commercial fishery weighs between
90 and 150 kilograms (1 kilogram equals 2.2 pounds). 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.
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.
Swordfish are pelagic fishliving
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
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
Florida and the Caribbean.
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
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.
Today, some swordfish are caught as they traditionally were using harpoons, but most are caught
on longlines consisting
of a main line, up to 40 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
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:
- Eat a variety of different
fish; don't restrict yourself to swordfish.
- Avoid eating excessive amounts
of any single type of fish.
- Avoid eating the internal
organs of the fishthey typically contain higher contaminant concentrations
than the flesh.
- When catching your own swordfish,
check and follow all applicable health advisories.
- High-risk individualspregnant
women, women of childbearing age, and children under age 15should
limit their consumption of swordfish. Pregnant or nursing mothers should
limit their consumption to once a month.
- 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.
International Commission for the Conservation
of Atlantic Tunas (ICCAT)manages swordfish fishery as well
to Rhode Island Sea Grant Fact Sheets