Aquarium of the Pacific - Online Learning Center - Species Print Sheet
Harbor seals are members of the family Phocidae. Lacking an external ear flap, members of this family are commonly called the true or earless seals. Fur seals in the family Otariidae, which includes fur seals and California sea lions, are known as eared seals. Earless seals cannot rotate their hind flippers under their bodies so they undulate when on dry land, keeping their flippers at their sides and trailing their hind flippers along unused.
This species has the broadest distribution of the pinniped group of animals. The term “pinniped” comes from the Latin “pinna”, meaning winged, and “ped”, meaning foot. There are five commonly recognized harbor seal subspecies based on geographic distribution: P. v. concolor, P. v. mellonae, P. v. steinegeri, P. v. vitulina., and P. v. richardii.The latter harbor seal subspecies is the one found in Southern California.
At the Aquarium
There are several harbor seals at the Aquarium. Shelby was two years old when she came to the Aquarium just before our June 1998 opening. Troy came to the Aquarium in 2007. Troy and Shelby are parents to Bixby, born at the Aquarium in 2012, and Toby, born at the Aquarium in 2013. Troy and Shelby are part of the Aquarium’s Southern California/Baja Gallery. They can be seen from the Seal and Sea Lion Tunnel on the first floor and at the outdoor amphitheater up the stairs between Shark Lagoon and the second floor. Bixby and Toby are currently on loan to other institutions for breeding purposes.
Pacific Ocean from Hokkaido, Japan, north to the Kamchatka Peninsula, across the Aleutian Island chain, the southern coast of Alaska, the western coast of Canada and the United States to the northern portion of Baja California, Mexico. Also western Atlantic Ocean from the central U.S. coast north to Canada, Greenland, Iceland, and northern Europe.
Because of its wide distribution, this species habitat varies from one area to another and is dependent in large part on haul out facilities, access to deep water, food supply, and protection from weather. These seals occupy a variety of habitats including sandy, rock and boulder-strewn beaches and a substantial range of climatic temperatures. Preferred hauling out areas include shores of sand, mud, gravel, rocks, reefs, and in some cases, glacial ice and ice floes. They tend to prefer beaches and sand bars that are bare at low tides.
The body of a harbor seal, often described as spindle-shaped, is fusiform in shape and round in cross section. Pectoral and pelvic limbs have been modified to become short flippers. The foreflippers end in five well developed claws. The head is round and relatively small. The muzzle is blunt when compared to the longer pointed snout of the California sea lion. The ear location is identified by a small hole on each side of the head. There is no external ear flap. Eyes are round and widely set on the front of the head. The hind flippers provide locomotion through the water and hide the short flat tail causing it to be almost invisible.
Harbor seals have a hairy coat consisting of stiff, heavy guard hairs, with a layer of finer, denser, hair underneath. The hair is not sufficient to provide temperature insulation, which is supplied by a thick layer of blubber.
Color and markings vary substantially from one animal to another and from latitude to latitude. They are unique to the individual seal just as fingerprints are in humans. Some show a light-colored background of almost white to silver or gray with darker circular or ring marks. Others may show a darker background with light-colored markings. In cold climates newborn pups are covered with a coat of white hair called lanugo, which is molted shortly after birth. In more temperate climates the lanugo is shed prior to birth.
Adult female harbor seals reach a length of 1.2 – 1.7 m (3.9 – 5.6 ft) and will weigh 50 to150 kg (110 to 331 lb). Males are larger with lengths of 1.4 – 2.0 m (4.6 – 6.6 ft) and weights from 70 to 170 kg (154 to 375 lb).
Harbor seals are opportunistic feeders and they are not fussy eaters. They require 5-6% of their body weight in food per day. They may spend up to 85 percent of the day diving for prey. Diet varies with geographic location and season. Primary food sources involve schooling and bottom dwelling fishes such as herring, various species of flatfish, surfperch, rockfish, salmon and hake. They are also partial to some invertebrates including cephalopods, other mollusks, and crustaceans. They fulfill their need for water from moisture in foods and if food supply is short, metabolism of fat aids in moisture production.
Reproductive activities of harbor seals are not well documented; however, strong bonds between a pup and its mother have been noted. Generally, females reach sexual maturity at a weight of about 50 kg (110.3 lb) at three to six years of age. Males become sexually mature at about 75 kg (165.3 lb) when they are three to seven years old.
Mating takes place in the water soon after pups have been weaned. Males generally mate with only one or a few females during the mating season of about one to nine weeks. Gestation is 9 to 11 months including a period of delayed implantation of one and a half to three months.
Pupping time varies with latitude and is mostly during the months of February through June. It is rare that a mother gives birth to more than one pup, but twinning does occur. (Troy, our youngest harbor seal, is a twin.). When there is a multiple birth, usually only the strongest pup survives as the mother cannot support two pups, and will not attempt to care for the weaker sibling. Surrogate mothers have been observed, but it is an extremely rare phenomenon. Pups are very precocious and most are able to crawl and even swim within an hour or two after birth.
The pups nurse for only about four to six weeks. They gain weight and strength at a rapid rate, more than doubling weight by the time they are weaned. Toward the end of the nursing period, pup and mother tend to lose interest in each other and weaning may be gradual or happen abruptly. After weaning, the mother abandons the pup abruptly. The pup usually does not stay in the natal area very long, leaving it to start exploring on its own, sometimes traveling fairly far from its birth place.
Most pinnipeds welcome the company of their own species or those that are closely related, but harbor seals are generally intolerant of close contact with other seals. Pups and juveniles commonly play and romp together, but away from the adults. As they increase in age they become more solitary in their behavior. During the molting period between spring and fall, depending on geographic location, they are more gregarious, hauling out in large numbers in the same area of beach or reef. When hauled out, they mostly sleep but remain aware of their surroundings and alert to possible dangers.
When in a group, they like a clear “living space” of about the length of their own bodies around them. If this space is impinged on, they will become agitated and vocalize by grunting, growling, and snorting. If these actions don’t bring the desired change, they may resort to head butting or even biting. Actual fighting is rare except among males during the mating season. The least vocal of all the pinnipeds, harbor seals do not “bark” as their California sea lion relatives do.
Harbor seals are graceful and agile swimmers, but are very awkward when on land. They are unable to move their hind flippers forward under their body and therefore cannot “walk” as their sea lion cousins can. Their land movement is similar to that of caterpillars and inchworms. It is accomplished by an undulating movement of the body. In spite of this handicap they can reach a very respectable speed when properly motivated. Propulsion while swimming is accomplished by a sculling motion of the hind flippers. The fore flippers are used for steering, i.e., directional control.
Curious, but wary, harbor seals are constantly alert to perceived dangers and will quickly vacate an area they consider unsafe. Not nearly as social as the sea lion group, they dislike being disturbed, even by their own kind, and most commonly avoid body contact except during the breeding season.
Harbor seals are well adapted to their marine lifestyle. A thick layer of blubber aids in temperature control. Body shape permits ease of movement through the water and limb development to flippers makes for efficient propulsion. They have little if any color vision, but their black and white vision is keen and is better in the water than out. Their whiskers or vibrissae are very sensitive to vibration and water motion and are an important part of sensory input when the animal is swimming in constricted areas or hunting for food.
Harbor seals and other pinnipeds have a material called myoglobin in their muscle tissues that has the ability to store relatively large quantities of oxygen. This aids the animals in deep dives and long periods under water. The myglobin can supply oxygen when other sources are depleted. They have the ability to direct oxygen-rich blood to critical organs where it is most needed.
Harbor seals have a maximum lifespan of 25 to 30 years, while males tend to have shorter lives than females. This may be explained by the stresses placed on the males during the breeding season.
It is estimated that about 21% of harbor seal pups do not survive their first year. This can be due to a variety of factors including illness, predation, maternal abandonment, extreme weather conditions and accidental injuries. Pups are especially subject to some land-based predators such as foxes, coyotes, bobcats, and even eagles. Both pups and adults may become food for large sharks, killer whales, and in some areas, polar bears.
Harbor seals are very sensitive to human encroachment and may be forced to abandon an ideal habitat for one less suitable to their well-being. Along with human pressures come pollution and other types of habitat degradation that can have negative influence on species viability.
There is presently no commercial harvesting of harbor seals, but there is a limited amount of native subsistence hunting. Some commercial fishers object to having seals steal fish from their nets and kill them to avoid loss of their catch. Seals are on occasion accidentally caught in fishnets as bycatch and die by drowning.
The last few decades have seen population adjustments throughout their range from increase to decrease to stable. While in some areas harbor seals are hunted for meat, skins, and oil, the Marine Mammal Protection Act of 1972 made it illegal to hunt or harass any marine mammal in US waters. The harbor seal is not listed by CITES. It is listed on the IUCN Red List as Lower Risk – Least Concern.
Harbor seals are known to sometimes follow fish runs upstream for many miles. They may stay in fresh water rivers most of the summer, depending on food supply, returning to salt water in late summer or early fall. On October 23, 1805, Clark of Lewis and Clark fame observed “sea otters” in the narrows of the Columbia River, more than 161 km (100 mi) from the Pacific Ocean. He later corrected his mistake in his journal—the animals were not sea otters, they were harbor seals! Today NOAA reports: “It’s common for seals and sea lions to follow prey species into fresh water upstream of Longview, Wash. (river mile 67), up to Willamette Falls (river mile129) and Bonneville Dam (river mile 145)”.
The whiskers, or vibrissae, of seals are very sensitive to vibration and water motion and are an important part of sensory input when an animal is swimming in constricted areas or hunting for food. Blind seals and sea lions rely on their vibrissae to ovoid obstacles and find prey.
Harbor seals may spend days at sea without hauling out. When sleeping in the water they float vertically with just their heads above the surface, a behavior called “bottling”.