Earless seals (family Phocidae) are marine mammals defined by their lack of external ear flaps. Their highly streamlined bodies allow them to move efficiently through water, enabling deep, sustained dives for hunting. This family is entirely carnivorous, and their survival is directly linked to the availability and abundance of prey in their diverse marine environments. Understanding the diet of these true seals requires looking closely at their general feeding methods and the specific animals they target.
General Characteristics of the Earless Seal Diet
Earless seals are opportunistic predators, meaning their diet is highly flexible and shifts based on the most abundant and accessible prey in their habitat. Their powerful hind flippers allow them to pursue fast-moving prey in the open ocean. To support their thick insulating layer of blubber, they must consume a large volume of food daily.
Their feeding strategy is adapted for underwater capture and immediate consumption, as they cannot chew their food. Most species employ pierce feeding, using sharp, conical teeth to grasp slippery prey items. This is often combined with suction feeding, where the seal expands its mouth cavity to pull smaller fish or invertebrates directly into the throat. Prey is typically swallowed whole or torn into large chunks, reflecting the grasping function of their teeth.
Primary Sources: Fish and Cephalopods
Fish form the foundational and most consistent component of the earless seal diet. The specific species consumed are determined by local availability, including schooling pelagic fish and slower benthic species. For instance, harbor seals frequently consume Atlantic herring, hake, flounder, and Pacific cod, often focusing on individuals less than 30 centimeters long.
Arctic species, such as the Ringed seal, rely heavily on cod species, including Arctic cod and saffron cod, particularly during the winter and spring. Other important fish prey across the family include capelin, salmon, rockfish, and sand lance. Seals are highly effective at utilizing their senses, often relying on sensitive whiskers (vibrissae) to detect the movements and vibrations of fish in dark or turbid water.
The second major food source is cephalopods, including various species of squid and octopus. Squid are a high-energy food item sought after by deep-diving species like elephant seals and Weddell seals, which can plunge hundreds of meters below the surface. The beaks of these cephalopods are often found in seal scat, providing researchers with direct evidence of consumption.
Specialized and Opportunistic Prey
While fish and cephalopods dominate, some species exhibit highly specialized feeding habits. Crustaceans are a substantial food source for several species, especially the Crabeater seal of the Antarctic, which primarily feeds on krill. Despite its name, this seal’s multi-cusped cheek teeth are shaped to act as a sieve, allowing it to filter vast quantities of krill from the water.
Coastal species, like the harbor seal, opportunistically consume mollusks and other benthic invertebrates, such as shrimp, crabs, and clams, using their powerful molars to crush the hard shells. The Leopard seal, an apex predator in the Antarctic, has a remarkably broad diet that includes warm-blooded prey. These large seals actively hunt and consume penguins and smaller pinnipeds, utilizing a grip-and-tear feeding strategy.