Gray seal

Class: Mammalia
Order: Pinnipedia
Family: Phocidae
Genus and Species: Halichoerus grypus
  • Gray seal floating with its head above the water
  • Gray seal reclining on a ledge in the water with its head above the water
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Gray seal

Also called horsehead seal, gray seals are amazingly dexterous swimmers, common on both sides of the North Atlantic.

Physical Description

Males have a distinctively arched Roman nose, which gives them their other common name of horsehead seal. Males have massive shoulders and necks with the skin bunched in large folds or wrinkles. Females lack the distinctive nose of the male and are more delicately featured. Coat color varies greatly from gray to brown, but most have darker backs than bellies. Bulls have a dark background color with lighter, irregular spotting seen mostly on the belly. Cows have a lighter background color with darker patches and spots. Gray seals lack extremely dense underfur that distinguishes the eared seals; they only have a few secondary hairs as opposed to the 50 or so found in fur seals.

Gray seals have many adaptations for their aquatic lifestyle. Their limbs are shortened with the digits elongated and encased in cartilage and connective tissue to form flippers. Their streamlined, torpedo-shaped body has strong, bulky shoulders and tapers to the tail. Seals generally have more bulk overall in the torso than sea lions, partially due to their method of swimming propulsion. Seals use their rear flippers and the back half of the body in a sculling motion. Gray seals have relatively short front flippers with five prominent claws and have the ability to curl these flippers to tear food or grasp terrain.

On land, seals move in caterpillar fashion alternately shifting weight from their chest to their pelvic region, or they will roll to their desired destination. They appear quite clumsy and slow but can overtake a running human over a short distance.

In water, gray seals make up for their clumsy appearance on land. A flexible body allows them to twist and turn easily while pursuing prey. Their front flippers act as rudders, but are kept tucked away close to the body when not in use. They are able to obtain speeds of 14 to 23 miles per hour (23 to 37 kilometers per hour), but normally cruise at six miles per hour (10 kilometers per hour) or less. They tend to exhibit deliberate and sluggish behavior to conserve energy, and are usually either traveling between haul-out spots, making feeding trips of short duration or resting. They often use an upright stance while resting in the water, called bottling.

Water is an efficient conductor of heat and seals must be able to regulate body temperature. A layer of blubber, or fat, insulates the trunk of their body while the circulation system has the ability to shunt the blood supply to the extremities and the outer surface of the body. As a result, they can haul out on ice and not melt it. Gray seals' dense fur gives them some protection from the cold as well as trapping a layer of water next to the skin that warms to body temperature. They also have a relatively small body surface area in proportion to their volume, reducing the amount of heat lost to the surroundings. They thermoregulate by behavioral means through methods such as changing position in the sun, moving to damp places or shallow pools, and altering activity levels.

Size

Adult males are about 7.5 feet (2.3 meters) in length and can weigh over 750 pounds (339 kilograms). Females are smaller with lengths about 6.5 feet (2 meters) and weigh up to about 575 pounds (170 kilograms).

Native Habitat

Gray seals are found on both sides of the North Atlantic in temperate and subarctic waters. They prefer remote rocky coasts with small islands and reefs. The beaches they inhabit may be rocky, sandy or ice pack. Gray seals migrate far from their rookeries when not breeding or molting.

Communication

Gray seals have numerous vocalizations, many of which are used during their highly social breeding season. Males jackhammer, hiss and growl to display dominance and aggression. They exhibit behaviors such as neck darts and open-mouthed threats as forms of non-vocal communication. Non-receptive females caterwaul or hoot at persistent males. Flipper slapping and scratching are common signs of irritation. Little is known about gray seals' sense of smell, but it should be noted that bulls produce strong odors during breeding season and that mothers identify their pups by scent. Olfactory, visual and acoustic cues are all part of the mother-pup recognition system. Tactile communication occurs as well, demonstrated through whisker greetings.

Food/Eating Habits

As predators, seals have excellent senses. Their eyesight is particularly well developed since they spend much time underwater with reduced light levels. On the surface, their pupil contracts to a tiny pinhole to protect the retina from any intense glare. They see better underwater than in air. Gray seals also hear better in their underwater environment and can perceive sound at a greater range of frequencies than humans. Lack of any external ear flaps and a heavy wax coating in their auditory canal reduces their ability to perceive sound in the air. Their ears are valvular and close when in the water. Their nostrils are also valvular and are closed at rest. The vibrissae located on the head are extremely sensitive and enable seals to capture prey in total darkness by feeling the currents created by their prey.

Gray seals have been documented as eating 29 different species of fish and invertebrates including herring, cod, mackerel and squid. They sometimes eat commercially valuable species, which makes them unpopular with fishermen. They regularly dive 230 feet (70 meters) for food, but are capable of diving much deeper.

At the Smithsonian's National Zoo, they are fed a combination of thawed frozen herring, capelin, butterfish, squid and mackerel twice a day. They receive vitamin supplements daily to replace any nutrients lost during the fish freezing process.

Social Structure

Gray seals are gregarious social animals that haul out close to one another and form large aggregations during the pupping, breeding and molting seasons.

Reproduction and Development

Breeding season differs among the populations, with the Northeast Atlantic group pupping mostly on land in September through November, the Northwest Atlantic group pupping on land and ice from late December to early February, and the Baltic group pupping on ice from February to March. About a month before pupping, large numbers of cows and bulls congregate offshore of the rookery. The birth of the first pups signals the males to come ashore. Instead of holding territories, the males compete for proximity to the females and their pups. Bulls display, vocalize, and fight, often trying to interrupt each other during copulation. Their large size and massive necks provide them with some protection from each other's shoving and biting. During the initial stages of the breeding season, bulls control large areas with many females. Once mating begins, the bulls become distracted and younger, smaller bulls can establish themselves on the fringes of the group. They mate mainly on land, though they can sometimes mate in the water.

Females give birth to a single pup of which they are very protective. Lactation lasts roughly three weeks and during this time, the mother spends most of her time in close proximity to her pup. Pups feed for about five minutes every five hours and gain weight rapidly on the high-fat milk. Once the pup is weaned, the cow comes into estrus and solicits attention from the bull. The fertilized egg develops into a blastocyst after which it remains dormant for two to four months before attaching to the uterine wall. This delayed implantation ensures that birthing occurs at the right time each year. Females then return to the sea to regain their physical condition before molting.

At birth, pups are about three to 3.5 feet (90 to 105 centimeters) long from nose to tail tip and weigh about 33 pounds (15 kilograms). They have a cream-colored natal lanugo coat that molts at two to three weeks. Pups gain about five pounds (2.3 kilograms) per day from their mother's rich milk, but gain little if any in length. At weaning, pups are completely abandoned by their mothers and fast from one to four weeks before they start feeding on their own at sea.

Neither bulls nor cows eat during the breeding season and both experience significant losses in weight and physical condition. Following breeding season, all gray seals return to the sea and begin their migrations. Young animals may travel as far as 30 miles (48 kilometers) in a day. Gray seals regain their physical condition before their annual molt. Adults probably return to their birthplace once sexually mature, which is age three to five years for females and six years for males.

Lifespan

Gray seals live an average of 35 years in human care while wild bulls average 25 and wild cows average 35. The oldest recorded in the wild is 46 years.

Gray seals' natural predators are sharks and orcas. Disease and parasites are also natural threats. Although gray seals are not hunted for their fur and there is no longer a market for seal oil, people continue to be the greatest threat to these animals. Entanglement in and ingestion of plastics results in unknown numbers of gray seal deaths. They are inadvertently caught in fishing nets, particularly drift nets, resulting in their deaths. The impact of overfishing in gray seals' natural hunting grounds has not been determined. They are unpopular with fishermen as these seals are known to consume commercially valuable fish.

At the seal exhibit, visitors can meet gray seal females Kjya, Kara and Birdie, as well as a male Gunther. Gunther has a Species Survival Plan recommendation to breed with Kjya and Kara. Birdie is Kara's offspring and was born on Jan. 21, 2017.