Phoca vitulina, commonly known as the harbor seal or common seal, is a marine mammals species belonging to the family Phocidae and order Carnivora. The genus name Phoca comes from the Greek ‘phōkē‘, meaning ‘seal’, while the species name ‘vitulina‘ derives from the Latin ‘vitulus‘, meaning ‘calf’, referring to the animal’s youthful and rounded appearance. This species has a wide distribution across the Northern Hemisphere, inhabiting both Atlantic and Pacific coasts, including the Baltic and North Seas. It primarily occupies temperate and cold coastal waters, using beaches, sandbanks, rocky areas, and ice floes as resting or breeding sites. Five subspecies are recognized, with notable populations in North America, Europe, East Asia, and some freshwater areas in Canada.
Morphologically, the Phoca vitulina has a robust and compact body, with a small, rounded head resembling that of a feline. Its nostrils form a distinctive inverted ‘V’, and its large eyes are close together. Although it lacks external ear flaps, the ear canal is visible behind the eye. Its whiskers (vibrissae) are long, light-colored, and bead-like in appearance. The fur shows great variability, ranging from light gray to dark brown, with unique spots, rings, and mottling patterns on each individual. Adult males reach up to 1.9 m in length and weigh around 150 kg, with females generally slightly smaller. It can be confused with similar species such as Pusa hispida (ringed seal) or Phoca largha (spotted seal), though nostril shape and spot patterns help differentiate them. In the Pacific region, distinguishing Phoca vitulina from Phoca largha can be especially challenging.
Phoca vitulina is an opportunistic predator feeding on a wide variety of marine prey. Its diet includes demersal and pelagic fish such as herring (Clupea harengus), cod (Gadus spp.), flatfish, hake, and salmonids (Oncorhynchus spp.), as well as cephalopods, crustaceans, and molluscs. It adapts easily to local conditions, feeding both in shallow waters and at depths greater than 500 meters. Occasional predation on seabirds, such as ducks, has been recorded. Its ability to travel long distances in search of food — even into freshwater — shows its great ecological versatility.
Reproduction in Phoca vitulina occurs once a year, with breeding season varying by latitude, typically from February to July. Mating takes place underwater and the system is thought to be polygynous. Following a gestation of about nine months (including delayed implantation), the female gives birth to a single, well-developed pup capable of swimming and diving within hours of birth. Lactation lasts between 3 and 6 weeks, during which the pup feeds on the mother’s rich, fatty milk and doubles its weight. The female returns to estrus shortly after weaning. Molting (shedding of fur) occurs after the reproductive period, requiring the animals to spend more time on land.
Phoca vitulina is one of the most studied pinniped species due to its broad distribution and proximity to urban areas. It has historically been hunted for its meat and skin, though many populations are now protected by laws such as the Marine Mammal Protection Act (USA) and the Conservation of Seals Act (UK). Despite protection, it faces threats including fishing net entanglement, heavy metal pollution, and outbreaks of viruses such as distemper. Some individuals, like ‘Hoover’ — a seal known for mimicking human speech — have gained popularity. Additionally, its role as a top predator helps maintain the balance of coastal ecosystems such as kelp forests, where it coexists with species like Strongylocentrotus (sea urchins) and Haliotis (abalones). It is recommended to keep a safe distance from resting sites as seals may abandon their pups if disturbed.
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