Seals are marine mammals that are adaptable predators found throughout the world’s oceans. Their diet is highly varied and opportunistic, allowing them to thrive in diverse marine environments. The specific composition of a seal’s diet is rarely fixed, instead shifting continuously based on the availability of local prey.
Core Prey Categories
The majority of seal species rely on three broad categories of marine life. Fish are the most common food source, especially small, schooling species. Prey includes forage fish like Atlantic herring, sand lance, and capelin, as well as demersal species such as cod, pollock, and hake.
Cephalopods, such as squid and octopus, constitute another significant portion of the diet, especially for seals foraging in deeper, offshore waters. Many seals also consume various crustaceans, including shrimp and small crabs, particularly in coastal habitats. For example, newly weaned Harbor Seal pups often target crustaceans before transitioning to larger fish.
Specialized Feeding Strategies
While most seals are generalist feeders, some species have evolved distinct diets to exploit unique prey. The Crabeater Seal is misnamed, as its diet consists almost entirely of Antarctic krill. This specialization is supported by unique, sieve-like teeth that interlock to strain krill from the water.
The Leopard Seal is a predator whose diet includes warm-blooded prey. While it consumes krill and fish, this Antarctic species actively hunts penguins, seizing them with large canine teeth. Leopard Seals have also been documented preying on the pups of other species, such as Antarctic Fur Seals, indicating a seasonal shift to larger prey.
Influence of Habitat and Species Variation
A seal’s geographical location and habitat determine what it eats. In temperate coastal zones, species like the Harbor Seal consume a diverse mix of fish, including flatfish and shellfish. Their diet often changes seasonally, adjusting to the migratory patterns and local abundance of prey like squid or salmon.
Arctic species must adapt to environments dominated by ice and limited prey. Harp Seals rely heavily on Arctic cod, polar cod, and pelagic amphipods, which are abundant beneath the ice. The Bearded Seal, an Arctic resident, favors benthic invertebrates like clams and sea cucumbers that it forages for along the seafloor.
Nutritional Needs and Consumption Rates
To maintain their large body size, seals must consume a significant amount of food daily when actively foraging. A typical adult Harbor Seal weighing 100 kilograms must consume 5 to 7 kilograms of food each day, roughly 5 to 6 percent of its total body weight. This intake meets the metabolic demands of living in cold water.
Seals are also adapted to periods of prolonged fasting, typically associated with breeding and molting seasons when they haul out onto land or ice. During these times, they rely entirely on metabolizing stored blubber for energy and water. Male Elephant Seals, for example, can fast for up to three months during breeding, losing body mass to maintain dominance.