Earless seals, commonly called true seals and classified in the family Phocidae, are marine mammals adapted to an amphibious life. They are one of the three groups of pinnipeds and are best known for their streamlined bodies, thick blubber, and the absence of external ear flaps. These features suit them for an efficient, primarily aquatic existence while still relying on land or sea ice for resting, breeding, and molting.
Key characteristics
- No external ears: earless seals lack visible pinnae; ears are internal.
- Limbs and locomotion: foreflippers are short and stabilizing; hind flippers point backward and provide main propulsion in water but limit mobility on land.
- Insulation: a thick blubber layer and dense fur insulate against cold; many species undergo an annual molt.
- Size and dimorphism: body size varies widely; some species show marked sexual size differences.
True seals swim primarily by undulating their bodies and kicking with their hind flippers. On land they move by wriggling or pulling themselves forward, a contrast with the more agile gait of eared seals (Otariidae). Diets are generally piscivorous or teuthophagous, with fish, squid and crustaceans forming the bulk of their prey. Several species are capable of deep or prolonged dives to forage.
Distribution, reproduction and life cycle
Earless seals occur in polar, temperate and some tropical waters; a few species, such as monk seals, inhabit warmer regions. Breeding strategies range from dense, competitive colonies to solitary or small-group pupping. Females typically give birth on land or ice and nurse energy-dense milk for a relatively brief but intense period while fasting. Pups are adapted to grow rapidly before entering the aquatic environment.
Taxonomy and origins: Phocidae comprises roughly eighteen species worldwide and forms one of the three pinniped families alongside otariids and the walrus. Fossil evidence indicates that true seals diversified during the Neogene and spread across ocean basins; their exact early history continues to be refined by paleontological research. For a broader context on the three pinniped families see pinniped families.
Conservation and human interactions
Many true seal populations were reduced by commercial sealing in past centuries; protection and management have allowed some recoveries while others remain at risk. Current threats include climate change, habitat disturbance, bycatch, pollution and disease. Conservation status varies by species, and international and local measures focus on habitat protection, pollution control and fisheries management to reduce incidental capture.