Seals are marine mammals found globally, inhabiting diverse aquatic environments from polar ice to temperate coastlines. As predators, they consume a range of prey, influencing marine food webs.
Seal Diet and Krill Consumption
While the idea of seals eating krill is often associated with these marine mammals, it is not a universal dietary staple for all seal species. The most notable example of a seal that primarily consumes krill is the crabeater seal ( Lobodon carcinophaga ), despite its misleading name. These seals, found around the Antarctic coast, have highly specialized teeth designed for filter-feeding.
Their postcanine teeth are finely divided, forming a sieve-like structure when their jaws close. This unique dental adaptation allows them to efficiently strain Antarctic krill (Euphausia superba) from seawater. They swim into dense krill swarms with their mouths open, then expel the water through the gaps in their teeth, trapping the tiny crustaceans inside. Krill can constitute over 90% of a crabeater seal’s diet, and they can consume up to 40 kg (88 pounds) of krill daily. Other seal species, such as leopard seals and Ross seals, may opportunistically consume krill, but it is not a primary food source.
Diverse Diets Across Seal Species
Beyond the krill-focused diet of the crabeater seal, the feeding habits of other seal species are remarkably diverse, adapting to their specific habitats and the availability of prey. Seals are opportunistic feeders, shifting their diet based on available food sources. This adaptability allows them to thrive in various marine settings.
For instance, harbor seals (Phoca vitulina) primarily consume a variety of fish, including species like haddock, pollock, saithe, herring, and flatfish. Their diet also includes shellfish and crustaceans, and it can vary seasonally and regionally depending on local prey availability.
Grey seals (Halichoerus grypus), found in the North Atlantic, also have a fish-heavy diet, with sand eels, cod, whiting, and herring being common prey. They are known to consume octopus and lobsters when available.
Elephant seals (Mirounga spp.), the largest carnivorans, predominantly feed on squid and fish, including rays and sharks. They hunt at great depths, with males often foraging along the continental shelf for benthic prey, while females may vary their routes in pursuit of moving prey in the open ocean.
Leopard seals (Hydrurga leptonyx), apex predators of the Antarctic, have a broad diet that includes krill, fish, squid, and even other marine mammals and birds like penguins and the pups of other seal species. Their teeth, while having sharp canines for hunting larger prey, also feature lobed molars that allow for filter-feeding on smaller items such as krill.