Swordfish are powerful, migratory predators found globally in tropical, temperate, and sometimes cold waters across the Atlantic, Pacific, and Indian Oceans. They are easily recognized by their distinctive, elongated, flat bill, which gives them their common name. Their presence spans a wide range of latitudes, typically from 60° North to 45° South. Understanding their diet provides insight into their role within marine ecosystems.
The Swordfish Diet: A Carnivorous Feast
Swordfish are opportunistic predators, with a diverse diet dependent on prey availability. Their primary food sources include schooling fish like Atlantic mackerel, barracudinas, silver hake, Atlantic herring, lanternfish, butterfish, bluefish, and sand lance. Squid also form a significant part of their diet, sometimes accounting for nearly one-fifth of stomach volume.
The specific composition of their diet can vary by location and year, reflecting differences in prey availability. For instance, studies in the Florida Straits show cephalopods, like Illex species and other ommastrephid squids, often dominate their diet by weight and number. Deep-water species like lanternfish and shallow-water fish like mullet are also consumed, highlighting their ability to forage across different depths. They also consume crustaceans.
Hunting Techniques and Adaptations
Swordfish use their elongated bill to capture prey. They use their “sword” to slash through schools of fish, stunning or injuring them. This technique allows them to incapacitate larger prey or disorient smaller fish before consuming them. Their streamlined bodies and powerful muscles enable them to achieve high speeds, reportedly up to 50 miles per hour, making them one of the fastest fish in the ocean.
They possess adaptations that aid in hunting, particularly in low-light conditions. Their large eyes are suited for detecting prey in dimly lit environments, as they often hunt at dawn, dusk, or throughout the night. They also have specialized organs near their eyes that warm their brain and eyes, enhancing vision and cognitive function in cold, deep water. This unique ability allows them to maintain high performance even in varying thermal conditions.
Where Swordfish Find Their Food
Swordfish inhabit open ocean environments, preferring temperate and tropical waters globally. They are migratory, moving to colder regions to feed in summer and returning to warmer waters for spawning. This seasonal movement allows them to exploit areas with abundant food resources.
They exhibit diel vertical migration. During the day, swordfish descend to deeper, cooler waters, sometimes over 1,000 meters deep. At night, they ascend to shallower, near-surface waters, typically less than 100 meters, to feed on schooling prey that also migrate vertically. This behavior allows them to follow their prey and access a wide range of food sources throughout the water column.
Diet Variation Across Life Stages
A swordfish’s diet changes across life stages, adapting to its increasing size and hunting capabilities. Newly hatched larval swordfish are small and primarily feed on zooplankton and other fish larvae. As they grow into juveniles, their diet shifts to include larger organisms.
Juvenile swordfish begin to consume small fish, squid, and pelagic crustaceans. This transitional diet prepares them for the diverse prey they will target as adults. As swordfish mature into adults, their diet expands to include a wider range of larger fish and squid, reflecting their development into apex predators of the open ocean.