Harbor Seal

Harbor seals mainly prey on fish such as cod, hake, mackerel, and herring. They will also eat octopus, squid, and crustaceans.

At the Zoo, sea lions are provided with Atlantic herring, capelin, and squid.

Seals receive all of the water they need from the fish they eat. However, the fish provided by the Zoo is flash-frozen after being caught, which can reduce its water content. To help make up for this loss and to offer enrichment, the seals also eat unflavored gelatin without any additives.

Harbor seals are one of the most widespread pinnipeds. Harbor seals can be found in the coastal waters throughout the Atlantic and Pacific Oceans, but only north of the equator.

Harbor seals are found in shallow waters along coastlines, in bays, and around rocky islands and estuaries. You can often spot them near piers, beaches, big rocks, islands, and sea ice, where they like to haul out and rest on land.

Predators of harbor seals include larger animals such as sharks, orcas, and polar bears. Haul-out sites, where seals come ashore, help protect them by reducing the time they spend in the water. However, there are still dangers on land. For instance, when mother seals are away searching for food, coyotes, bears, sea lions, and wolves might prey on the seal pups.

Historically, people organized hunting and extermination programs to get rid of harbor seals because they were seen as competition for commercial fisheries. Fortunately, these programs have mostly stopped. Recently, there have been major die-offs of harbor seals, with thousands of them dying from diseases that were not a problem before. Since harbor seals rest on land, they can catch diseases from wild animals, pets, and human waste. Harbor seals are also very sensitive to pollution, which can build up in their bodies and cause serious health issues or even death. Furthermore, noise and other disturbances from human activities can hurt their ability to find food and reproduce.

Harbor seals have spotted coats in various colors, such as white, silver-gray, black, and dark brown. Males are slightly larger than females. They have narrow nostrils that can close while swimming. Harbor seals' eyes are adapted for seeing in dark or muddy water. They also use their sensitive whiskers, called vibrissae, to find food, particularly in deep or dark environments. They have long, flat flippers with five webbed digits on each.

On land, harbor seals move by flopping on their bellies because their flippers are small and cannot hold their body weight. In the water, they swim using all four flippers. They push forward with their hind flippers and use their front flippers for steering. They can swim forward and upside down, but they rarely swim backward. Harbor seals can reach up to 12 miles per hour but usually swim slower.

An adult harbor seal can hold its breath underwater for up to 30 minutes, but most dives last about three minutes. Like many marine mammals, harbor seals have a breathing pattern that includes a short exhale, a short inhale, and a longer breath-holding period called apnea. They have adaptations that help them save oxygen while swimming, such as slowing down their heart rate and pulling oxygen-rich blood to their organs.

Harbor seals have ways to control their body temperature. A thick layer of blubber keeps them warm by reducing heat loss. Blubber also helps streamline their bodies and is an energy reserve during fasting. When they are on land, the blood vessels in their skin can open up to release heat.

Harbor seals usually return to the same places to breed each year. Mating happens from late spring to fall. Before they have pups, male and female harbor seals show signs of wanting to mate, such as rolling on the ground, blowing bubbles, and playfully nipping at each other’s necks. Males may mate with multiple females, and they typically mate in the water.

Harbor seals have a unique way of becoming pregnant called delayed implantation. This means that after a fertilized egg forms, it doesn’t attach to the mother’s uterus right away. This allows the mother to become pregnant when there is plenty of food available. If food is limited, females usually do not have pups.

Female harbor seals generally give birth on land, on ice, or in shallow water close to shore. At birth, their pups are well-developed, with open eyes, weighing between 18 to 26 pounds and measuring 30 to 39 inches long. The pups can swim and follow their mothers right away. They nurse for about four to six weeks. Their mother’s milk is very rich, containing up to 45% fat, which helps the pups more than double their weight by the time they are weaned. Unlike other seal species, harbor seal mothers do not stay with their pups all the time while nursing; they leave to find food in the ocean. Scientists think they do this because their smaller size doesn’t let them store enough fat to go without food for too long.

During the nursing period, the mother is very caring and often nudges her pup. The pup might ride on her back, bite at her flippers, or chase her through the water. Once the pup is weaned, the mother shows little interest in it. After weaning, the pup learns to catch shrimp and small crustaceans, and later, it learns how to catch fish.

Harbor seals are quieter compared to other pinniped species. They make sounds like snorting, growling, and grunting. They can hear very well, especially when they are in the water, which helps them stay safe from predators. Scientists think that harbor seals also have a strong sense of smell when they're on land, which is important for mother seals to find and recognize their pups.

Unlike many other pinnipeds, this species tends to be solitary. Harbor seals can sleep in the water and spend equal time on land and in the water. Harbor seals can dive to depths of over 650 feet for as long as 40 minutes. However, their average dive lasts between three and seven minutes and is usually shallow. They typically do not dive to great depths since most of their food is found in shallower waters.