Harbour seals are marine mammals found in coastal waters across the Northern Hemisphere. They are often seen resting on shorelines or swimming underwater.
Defining Characteristics
Harbour seals have a rounded head and a blunt, dog-like snout. Their coloration varies widely, ranging from light tan, silver, or blue-gray with dark speckling to a dark background with light rings or spots. Adults measure about 5 to 6 feet (1.5 to 1.8 meters) in length and can weigh between 180 to 285 pounds (82 to 129 kilograms).
They lack external ear flaps, having only a small ear canal opening. Their nostrils are V-shaped, and their bodies are covered in short, stiff fur. Their foreflippers are short and webbed, while their hind flippers are used for propulsion in water. On land, their fused pelvic bones prevent them from rotating their hind flippers forward, leading to a caterpillar-like undulating movement.
Habitat and Range
Harbour seals are widely distributed across temperate and Arctic coastal waters of the Northern Hemisphere, including the Atlantic, Pacific, Baltic, and North Seas. They prefer diverse coastal environments, such as estuaries, bays, and rocky shorelines. Their adaptability allows them to tolerate both freshwater and saltwater, with some populations residing in inland freshwater lakes.
These seals regularly use specific locations, known as haul-out sites, including beaches, rocks, mudflats, or drifting ice. These sites are used for resting, regulating body temperature, molting, and giving birth. While they generally stay within 12 miles (20 kilometers) of the coast, some individuals can travel hundreds of miles.
Diet and Hunting
Harbour seals are carnivores with a varied diet of fish, such as herring, cod, mackerel, and flounder. Their diet also includes crustaceans like crabs and shrimp, and mollusks such as squid and octopus. They obtain water directly from their food.
When hunting, harbour seals use their keen underwater vision and hearing. Their sensitive whiskers, called vibrissae, help them detect vibrations in the water, allowing them to locate prey even in murky conditions. While they can dive to depths exceeding 1,500 feet (480 meters) and remain submerged for over 20 minutes, most foraging dives are shallower, less than 65 feet (20 meters) and lasting about four minutes.
Life Cycle and Behavior
Harbour seals are solitary in water but gather at haul-out sites for resting and social interaction. Even in groups, they maintain personal space. They are not highly vocal, but use vocalizations during breeding and mother-pup interactions.
Their bodies are adapted for aquatic life, using hind flippers for propulsion and foreflippers for steering. They can swim up to 12 miles per hour (19 kph) for short bursts. Harbour seals sleep in the water, in a position called “bottlenosing,” where their bodies remain submerged with only their heads exposed to breathe.
Reproduction occurs underwater, with females giving birth to a single pup annually after a gestation period of 9 to 11 months. Pups are born well-developed, weighing 24 pounds (11 kg), and can swim and dive within hours of birth. The mother provides milk, and the nursing period is short, lasting four to six weeks, after which the pup is weaned. Females can live for 30 to 35 years, while males live 20 to 25 years.
Conservation Status
Globally, the harbour seal is classified by the IUCN as a species of “Least Concern,” indicating a stable population. However, population trends can vary significantly by region, with some areas experiencing declines. These marine mammals face a range of threats, largely stemming from human activities.
Habitat degradation, including coastal development and pollution from oil spills and chemical contaminants, poses a risk. Entanglement in fishing gear is a danger, leading to injuries or drowning. Climate change impacts their environment by altering prey availability and affecting the stability of important haul-out sites. Human disturbance, particularly at sensitive resting and pupping areas, can also stress seal populations. Conservation efforts involve monitoring populations and implementing protective measures under acts like the Marine Mammal Protection Act.