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Shetland Sea Mammal Group

 

 

Seals in Shetland

The most numerous marine mammals in Shetland waters are two species of seal - the Grey Seal and the Common Seal or Harbour Seal. The old Shetland name for the Grey Seal is 'haaf fish' (deep sea fish), because it prefers more open sea conditions, while the Common Seal is known as 'tang fish' (seaweed fish) because of its preference for more sheltered shores and islands. Contrary to expectations, there are fewer Common Seals than Grey Seals in Britain as a whole, with around 28,000 Common and 105,000 Grey. In Shetland the situation is reversed with 6,000 Common Seals and 3,500 Grey Seals. 

It is possible to age seals quite accurately by counting the growth rings round the roots of the back teeth. Most of the information about how long seals live comes from seals that have been kept in zoos. The oldest recorded seal in the world came from Shetland, a grizzled old female who lived to the ripe age of 46 years! 

Seals have been around Shetland for many years with bones found at the Jarlshof settlement dating back to the Iron Age. There is also a lot of folklore surrounding 'selkies' coming ashore having cast off their skins and been transformed into beautiful people, and many an islander would fall in love with a 'selkie' and go back to the sea with them, traditionally this only happened at midsummer. In years gone by Shetlanders have hunted seals for their blubber, used for oil, their skins which were used to make clothes, and occasionally the flesh would be eaten. Most recently seals have been hunted for their valuable pelts.

Most valuable is the skin of a pup, particularly of the Common Seal, or the adult just after moulting, providing it had not been scared. The Common Seal was hunted the most partly due to the fact that the pups were found on easily accessible shorelines and also because until 1970 you did not need a permit to hunt Common Seal whereas you did for Grey Seals. Seal hunting was particularly common after the Second World War as times were hard and the demand for sealskins kept the prices high. Between 1956 and 1967 the recorded number of Common Seals dropped from 428 to 141 at Fitful Head and, although the figures from elsewhere are not so accurate, the same decline was seen throughout the islands. 

It was about this time that a Seal Conservation Act (1970) was introduced which meant a permit was required to hunt Common Seals and a closed season was imposed from 1 June to 31 August when it is unlawful to injure, kill or take a seal, with exceptions to this for seals killed in the vicinity of nets etc., to prevent them damaging fishing equipment and those seals killed under license for scientific or management purposes. The following year, 1971, a Shetland-wide survey showed that the numbers of Common Seals had fallen to just 1800, there was also concern about the selective pup hunting which over several years had resulted in an aging population and few females being recruited to the breeding population each year. These concerns, resulted in 1973 in a total ban on hunting, which was revoked in 1998, following scientific advice that seal numbers around Shetland had recovered following the over-exploitation which had occurred decades earlier.

The diet of seals has been studied by bodies such as the Sea Mammal Research Unit and Aberdeen University. Grey seals have been shown to predate heavily on the sandeel, which is important in the diets of many marine animals in the North Sea. Around the Outer Hebrides grey seal diets have been found to contain more Gadidae fish (the cod-like fish) than around Orkney or the Southern North Sea grey seal sites.

A local research project funded by the Shetland Wildlife Fund, Ministry of Agriculture, Fisheries and Food, Scottish Natural Heritage, the Scottish Association for Marine Science, the Hunter & Morrison Trust and the Shetland Fishermen's Association have examined the diets of Common Seals around Shetland. Analysis of droppings indicates which fish they eat, the size of the fish consumed and how much of the commercially important species are being consumed. 

Grey Seal    Halichoreus griseus

The most numerous of the seals in Shetland waters, this species is found around almost the entire coastline although the largest numbers usually frequent the more sheltered east coast. The last full survey of pupping sites in Shetland was carried out in 1983 when a total of 1000 pups were counted which equates to c.3,500 animals in total.

The total U.K. population was estimated as 108,500 in 1994, and of these 99,300 were found in Scottish colonies. Good places to see this species are at Sumburgh Head where 500+ may be hauled out on the rocks at the base of the cliffs during the summer, or around Lerwick Harbour where they are opportunistic feeders around the fish processing factories on the shoreline, although they may be found in most sheltered bays and voes.

Grey Seals give birth to their pups fairly late in the year, around October, usually on beaches at the foot of cliffs. When the Grey Seal pup is born it has a white furry coat which it sheds after about 3 weeks. At this time it is not a particularly proficient swimmer. The pup will feed from her for about 16-21 days and during this period and immediately after breeding, both the males and females do not eat and can lose quite a lot of weight. Immediately after this they have a period of feeding between late November and mid-January when they regain condition and it is only then that they undergo their annual moult. Females tend to moult in early February with the males later in mid-March and it is at this time they spend long periods hauled out, though not at their breeding sites.

Common Seal    Phoca vitulina  

The Shetland population of the Common Seal was last counted in 1997 using the 'hi-tech' method of an aerial thermal image survey of the coastline. A total of 6,000 were counted. This is a minimum figure as only those animals hauled out on rocks are recorded in this way, although this is thought to represent between 60-80% of the total population.

The current UK population estimate of the species is 28,000 animals. As with Grey seals the species is found around the majority of the Shetland coastline although some of the largest concentrations are around Fitful Head (south Mainland), the isle of Mousa (where they are very easy to see), and the north Mainland coastline.

Common Seals usually give birth to their pups in June, hauled out on the shore between tide marks. The pups have already shed their white furry coats before birth and are able to swim well from birth. Common Seal mothers tend to be more attentive to their offspring and will if necessary dive while holding onto the pup if threatened. The pup will continue to feed from it's mother for about 4-6 weeks. The pup will continue to feed from it's mother for about 4-6 weeks, at which point the female will become sexually receptive and mate with a male, around this time or before, the mother will abandon the pup to fend for itself. The peak of mating in common seals is visible at haul-out sites such as on Mousa, there is a sharp rise in the incidence of mature males with fresh bloody scaring on their necks and hind-flippers.

Common Seals begin moulting during July and finish during September, females and young animals moult first, followed by males and finally sexually mature males are the last to undergo the moult during September.
 

Distinguishing between Grey and Common Seals

Grey and Common Seals can be quite difficult to tell apart, although with practice it can be reasonably straightforward. Size is one factor distinguishing the two - Grey Seals are usually much bigger with a fully grown adult male or bull reaching 2.2m in length and weighing 220kgs, the females reaching 1.8m and weighing 150kg; the fully grown male Common Seal only reaches 1.5-1.8m and weighs 113kg with the female reaching 1.2-1.5m and weighing 113kg. There are also differences in the colour and patterns of the fur, although this feature is extremely variable and can vary with the sex, age, whether or not the fur is wet or dry and whether the animal is moulting (shedding and replacing) it's coat.

Probably the easiest way to tell them apart is the shape of the head. The Grey Seal has a much larger head with a high muzzle often referred to as a Roman nose; whereas the Common Seal has a low dog-like muzzle with a relatively rounded head and distinct forehead producing a much more appealing and expressive appearance. The nostrils of the Common Seal form a 'V' shape while the Grey's are much more parallel. The difference between the two species is not limited to their appearance, they also tend to have different habits. 

Grey Seal (left) and Common Seal (right) facial characteristics

   

  

What to do if you find a stranded or injured seal in Shetland

Occasionally, seals may become entangled in fishing gear and may suffer shock, which can kill them. You can help by taking appropriate action: When seals become entangled in fishing gear offshore, it will take patience and time to release them. It is best done at the surface of the water so that the effective weight is less. If the seal is caught in a trawl or drift net do not lift it out of the water on to the deck if it appears to be active and alert, as it may suffer respiratory collapse or cardiac arrest. Never tow a seal to harbour if this can be avoided. Always ensure that all net and line has been removed from the seal before releasing it.

Seals found stranded on beaches are sometimes already dead, but may be injured. Look for wounds such as those made by boat propellers or sharks. Young seals in particular may be exhausted, disorientated or shocked. If you find a seal in this condition contact the Hillswick Wildlife Sanctuary, The Booth, Hillswick, Shetland. (01806) 503348, who will be able to advise or arrange suitable rehabilitation.

 

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