Seals, fascinating marine mammals, are carnivores that navigate diverse aquatic environments to find sustenance. Their diet is varied, reflecting the wide range of habitats they occupy globally. The specific food sources they target depend on their species, geographical location, and prey availability.
Primary Dietary Components
Fish forms a substantial part of the diet for many seal species. Common fish consumed include cod, herring, mackerel, and salmon. Harbor seals, for example, eat rockfish, flounder, and hake, demonstrating a preference for both schooling and bottom-dwelling fish. Their diet can fluctuate seasonally and regionally based on fish abundance.
Cephalopods, such as squid and octopus, are also significant dietary components. Elephant seals consume various squid species, which can make up a substantial portion of their diet. Other seals, like the Australian fur seal, include squid and cuttlefish, alongside fish.
Crustaceans, including krill and crabs, contribute to seal diets. Crabeater seals, despite their name, primarily consume Antarctic krill, which can constitute over 90% of their diet. These seals have evolved unique teeth to filter krill from the water. Some seal species also eat prawns, shrimp, and silverfish.
While fish, cephalopods, and crustaceans are common, some seal species incorporate other prey. Leopard seals prey on birds, particularly penguins, and even other marine mammals like smaller seals. For most seal species, however, warm-blooded prey is less common, with their diet predominantly consisting of marine invertebrates and fish.
Dietary Adaptations and Specializations
Seal diets exhibit variation influenced by species-specific evolution and environmental factors. Crabeater seals possess a specialized sieve-like tooth structure, similar to baleen whales, enabling them to filter krill from the water. This adaptation allows them to thrive on krill, which makes up the majority of their diet.
Leopard seals are apex predators with sharp, saw-like teeth suited for tearing flesh, consuming penguins, other seals, fish, and squid. Their back molars also allow them to filter krill when larger prey is scarce. This flexibility allows them to consume a wide range of prey, from krill to warm-blooded animals.
Geographical location also shapes a seal’s diet. Seals in colder Arctic and Antarctic waters, such as ringed and harp seals, consume more fish and crustaceans. Seals in warmer waters, like monk seals, often have a more diverse diet due to broader prey availability.
Diet also changes with age, size, and seasonal prey availability. Younger seals target smaller prey, while adults pursue bigger prey. For example, harbor seals’ diet can shift from pelagic sources in spring to a benthic-based diet in summer. Specialized teeth and diving capabilities enable seals to access specific food sources.
Hunting Strategies
Seals employ strategies to locate and capture prey underwater. Their diving abilities allow them to reach depths and remain submerged for extended periods. Elephant seals dive up to 1,700 meters and can hold their breath for two hours while foraging. Weddell seals reach depths over 900 meters with dives lasting up to 96 minutes.
While underwater vision and hearing are important, their sensitive whiskers, known as vibrissae, are adapted for hunting in dark or murky waters. These whiskers contain numerous nerve endings and detect subtle movements and vibrations. Seals use whiskers to follow hydrodynamic trails left by swimming fish, even when visibility is limited. Experiments show seals can hunt effectively using only their whiskers, even when blindfolded.
Seals often hunt solitarily and opportunistically. Some common seals forage in shallow coastal waters, on the seabed, or in mid-water. They may swallow smaller prey whole underwater or bring larger catches to the surface to tear them apart. Some species, like the ribbon seal, pierce prey with their teeth and swallow it whole.
Their whiskers are specialized; they are oval-shaped with a wavy pattern that prevents vibration from the seal’s own movement. This makes them effective at detecting external disturbances, enabling seals to precisely identify the size, speed, and direction of potential prey. Studies observe elephant seals extending whiskers forward in the deep ocean, suggesting rhythmic movements are a key hunting strategy in dark environments.