GRAY SEAL

 

Gray Seal Food Web In Baltic Sea

The grey seal (Halichoerus grypus) is a large seal of the family Phocidae, which are commonly referred to as "true seals" or "earless seals". The only species classified in the genus Halichoerus, it is found on both shores of the North Atlantic Ocean. In Latin, Halichoerus grypus means "hook-nosed sea pig". Its name is spelled gray seal in the United States; it is also known as Atlantic seal and the horsehead seal.

Sub Species

There are two Recognized Subspecies Of this Seal:

H. g. grypus in the Baltic Sea; and

H. g. Atlantica in the Western and Eastern North Atlantic Stock.

The type specimen of H. g. grypus (Zoological Museum of Copenhagen specimen ZMUC M11-1525, caught in 1788 off the island of Amager, Danish part of the Baltic Sea) was believed lost for many years, but was rediscovered in 2016, and a DNA test showed it belonged to a Baltic Sea specimen rather than from Greenland, as had previously been assumed (because it was first described in Otto Fabricius' book on the animals in Greenland: Fauna Groenlandica).

The name H. g. grypus was therefore transferred to the Baltic subspecies (replacing H. g. macrorhynchus), and the name H. g. atlantica resurrected for the Atlantic subspecies. Molecular studies have indicated that the eastern and western Atlantic populations have been genetically distinct for at least one million years, and could potentially be considered separate subspecies.

Distinctive characteristics

Gray seals are robust and sexually dimorphic; males grow noticeably larger, with a proportionately larger and broader head. The most distinctive features are the muzzle and head. The muzzle is particularly long, and wide at the end, with a fleshy mystacial area. In adult males, the top of the muzzle is convex. In adult females and subadults, the top of the muzzle is variable and can be flat, slightly convex (as in adult males), or slightly concave; the last case produces a barely noticeable forehead. The shape of the head has led to the locally-used common name “horsehead.” The nostrils are widely separated and almost parallel to each other, forming a “W” pattern as opposed to the “V” of seals of the genus Phoca. The eyes are small in proportion to the size of the head, widely-separated, and due to the length of the muzzle, proportionately farther back from the nose than on other phocids that share the gray seal’s range. The fore flippers are short, and on adult males wide and relatively thick. Adult males are also thicker through the neck than females.

Pelage color and pattern are variable between the sexes and age classes. Most gray seals are shades of gray, slightly darker above than below. There are usually numerous irregular dark blotches and spots on the back and sometimes a few below, although some females with very few spots appear to be solid grayish cream color. Males darken with age, becoming dark brown to blackish, with a variable number of lighter blotches and spots. Orange to reddish coloration can be seen on the neck, undersides, and flippers of some animals. Gray seals appear paler and duller in coloration just prior to the annual molt. Newborns have a silky, creamy-white lanugo, occasionally with a grayish tinge. The lanugo is molted in 2-4 weeks, and is replaced by a pelage like that of the female, but with more subtle markings.

Dental formula                    I 3/2, C1/1, PC 5-6/5.

Size

Adult males are up to 2.3 m long and weigh 170-310 kg, females average 2 m and 105-186 kg. Pups are 90-105 cm and 11-20 kg at birth.

Life Span

In Wild: Both male and female live up to 15-25 years.

In captivity: Male live up to 43 years.

Captive grey seal being fed, showing snout shape

Gestation Period       335 days.  

Can be confused with

Five phocids share the gray seal’s range. The gray seal is larger, with a relatively larger head and longer muzzle, widely-separated eyes and eyes set far back from the end of the muzzle. They also have distinctly different pelage markings than harbor, harp, and ringed seals. The shape of the head, nose, and muzzle, placement of the eyes, and overall color and markings also facilitate separation of gray seals from similar-sized bearded and hooded seals.

Distribution

Gray seals have a cold temperate to subarctic distribution in the North Atlantic. There are three somewhat isolated stocks: a western Atlantic stock centered in northeastern North America; an eastern Atlantic stock split between Iceland, the Faroe Islands, Norway, the United Kingdom, and Ireland; and a Baltic Sea stock. At sea, gray seals generally spend their time in coastal waters. When out of the water they haul-out on isolated beaches and rocky ledges of islands, and will also haul-out and give birth on shore-fast and pack ice.

Ecology and behavior

Gray seals are polygynous, but males do not defend territories or herd females. They actively compete for access to females using vocalizations, threat gestures, and occasional fighting. Pupping and breeding occur between late September and early March, depending on location. Gray seals breed earliest in the British Isles, followed by those in Norway and Iceland, and finally by those off Canada, and in the Baltic Sea. The single pup is usually attended continuously by its mother and weaned in 15-20 days, at which time many have quadrupled their birth weight of 11-20 kg. After weaning the pups remain ashore fasting for two to four weeks before dispersing to sea and wandering widely.

Many, but not all gray seals disperse from their rookeries during the non-breeding season, but gather again at traditional sites to haul-out for the annual molt. They are usually quite gregarious at haul-outs with groups of 100 or more being common, and they will share haul-outs with harbor seals. When ashore gray seals do not lie in contact with each other.

At sea they are usually solitary, or found in small dispersed groups. They will rest at the surface in a vertical “bottle” position, treading water with only the head and upper neck exposed. The maximum depth of dives is approximately 300 meters and up to 30 minutes. Most dives are from one to ten minutes, and to 60 meters or less.

Predation

Grey seals are vulnerable to typical predators for a pinniped mammal; their primary predator would be the orca or killer whale, but certain large species of sharks are known to prey on grey seals in North American waters, particularly great white sharks and bull sharks but also, upon evidence, additionally Greenland sharks. Some grey seal carcasses have washed ashore with visible “cookie cutter” bite marks, a tell-tale sign of attack by a Greenland shark (also called the sleeper shark). In the waters of Great Britain, grey seals are a fairly common prey species for killer whales. Apparently, grey seal pups are sometimes taken from beach colonies by white-tailed eagles, and golden eagles, as well.

Feeding and prey

Gray seals feed on a wide variety of benthic and demersal prey in coastal areas. They also feed on schooling fish in the water column, and occasionally take seabirds. Prey species taken include: sand lance, whiting, saury, smelt, various kinds of skates, capelin, lumpfish, pollock, cod, haddock, saithe, plaice, flounder, salmon, and a variety of cephalood and molluscan invertebrates. Cannibalism by adult males on pups has been reported.

Exploitation

Large-scale commercial hunting of gray seals has not taken place in recent years. Nova Scotia, however, requested permission from the Canadian government to kill 25,000 gray seals per year for the next 3 years to market seal products. Additionally, in 1999, the Canadian Fisheries Resource Conservation Council requested an experimental commercial seal hunt of up to 20,000 gray seals on Sable Island.

Since 1999, the Canadian government permitted the killing of a few hundred gray seals per year in areas other than Sable Island, and is considering additional proposals for gray seal hunts. In 2000 the Norwegian government gave permission for 400 gray seals to be hunted on the coast of Western Norway, in spite of the unknown population numbers. The purpose of this hunt was to determine whether interest in seal hunting exists.

In spite of a lack of scientific evidence, the fishing industry claims that seal predation is responsible for reduced fish stocks in Canada, the United Kingdom, and Ireland, and has requested that gray seal populations be “culled.” Requests to cull gray seal populations have also been made because these seals can apparently act as hosts to the codworm parasite, and a seal population reduction is thought by some to help reduce codworm infestation in cod and flatfish stocks.

Additional threats to gray seals on both sides of the Atlantic include shooting to prevent seal damage to fishing nets, traps, and catches. In the United Kingdom, fishermen are not required to report seal shootings under the “Fisheries Defence Clause” of the Conservation of Seals Act, so little is known about the scale of such killing in the U.K.

Official statistics show that more than 60 gray, Halichoerus grypus, and harbor seals, Phoca vitulina, were legally shot in 2000 under license by the Scottish fishery, the highest number in more than a decade. However the official figures may not include large numbers of both species, estimated by some organizations at several thousand seals shot under the Fisheries Defence Clause each year in Scotland. The government in Finland also allows the hunting of gray seals claiming that hunting protects fish stocks. Conservation groups are promoting the development and use of humane non-lethal seal deterrence methods such as anti-predator nets on fish farms. Conservation groups also argue that blaming reduced fish stocks on seal predation is merely a way to deflect attention from the fact that overfishing is the real problem.

Gray seals are also shot illegally as demonstrated by the shooting of 25 pups at a breeding rookery in the Scottish Orkney Islands in 1996. These seals are also at-risk of marine pollution such as organochlorines and oil spills, the latter which can cause acute respiratory distress. Oil contamination of gray seals is a severe problem in the Froan breeding area off central Norway. Between 30-60% of pups have become oil-fouled during their first month of life there.

Entanglement in marine debris is also a problem throughout the gray seal’s range. In the Gulf of Maine, an estimated average of 75 gray seals were killed by entanglement each year between 1994 and 1998. In Canada, gray seals are found entangled in nets of groundfish and salmon gillnet fisheries. Spanish deep water trawl fisheries off Canada have also entangled gray seals. The number of seals entangled decreased following the Greenland salmon gillnet and Atlantic Canada cod trap fisheries ended in 1993. Entanglement of gray seals in the nets of monkfish fishermen in Cornwall, England. The number of gray seals entangled in the area’s monkfish nets is estimated to be higher than the number of gray seals born there each year.

In 2000, rescue centers in Ireland and Wales reported rescuing record numbers of gray seal pups. The pups suffered a variety of conditions such as milky white eyes, mouth ulcers, swelling in the lower jaw and gums, crumbling jaws, brittle bones, and flu-like symptoms. In 2001 increased sightings of various seal species, including gray seals, were reported along the eastern seaboard of the United States, including seals needing rescue and rehabilitation. Cleaner habitats and/or reduced hunting may be the reason for the increase in populations. Increased commercial fishing in northern waters has also been cited as the reason because it causes seals to travel further south for food. Many of the seals in need of rescue were undernourished pups, and injured adults.

The gray seal is listed as a protected species under Annex II and Annex V of the European Community’s (EC) Habitats Directive. Several gray seal habitats have been proposed by EC member countries as Special Areas of Conservation under the Habitats Directive. The gray seal is also listed as an Appendix III species under the Bern Convention. The Scottish Wildlife Trust purchased Linga Holm, a 56-hectare uninhabited island in the Scottish Orkney Islands, to establish the world’s 3rd largest island-based gray seal breeding colony as a sanctuary for gray seals. The Trust monitors the seals’ progress, protects them from threats, including requests for culls, and is working to increase legal protection for the island’s gray seal population.

Hunting and severe pollution in the Baltic Sea has drastically reduced gray seal populations, although the population appears to be recovering.

In 1998, hunting of gray seals was banned in the Baltic Sea by the Helsinki Convention, however Finland and Sweden have recently called for the ban to be lifted in spite of scientific data published in 1997 that showed any amount of hunting Baltic gray seal populations would not be sustainable.

This species remains threatened by the level of pollution in the Baltic Sea by organ chlorines often found in seal blubber that can cause reproductive failure. The pollution in the Baltic Sea has improved over the last 2 decades, however pollution-related illnesses, such as severe intestinal ulcers, still affect these seals.

Threats and status

At present, most gray seal populations are healthy and growing, and the worldwide population is estimated at about 220,000. A notable exception is the Baltic Sea population, which once numbered 100,000 and is now only a few thousand, having never recovered from sealing and poaching in the early 20th century. Most gray seal populations experienced similar hunting pressures during this period, largely because of the payment of government-sponsored bounties to hunters. Bounties were established to control gray seal populations that were deemed to directly (through feeding) or indirectly (as a vector for seal, or cod worm, a destructive parasite) damage important commercial fisheries. Prior to bounty and commercial hunting, gray seals were locally important in subsistence harvests throughout the history of their contact with humans.

Gray seal mortality has also been attributed to distemper virus outbreaks that caused severe mortality in harbor seals. As a coastal species, gray seals are exposed to and ingest industrial and agricultural pollutants through the food chain. This may have an effect on their immune system and other aspects of health and reproduction. Entanglement in fishing nets is another source of mortality. Interestingly, human over-exploitation of North Atlantic sharks may have had the effect of helping gray seal populations grow and recover by increasing survival, particularly of newly weaned pups and juveniles.

Factors hypothesized include

The direct and indirect effects of large-scale commercial fisheries on key prey species, long –term ecosystem shifts, and changes in behavior by a primary predator, the killer whale, or a combination of these factors.

IUCN status                    Least Concern

Female With Pup

Male