Marine Mammals of the Hebrides

The seas around the Hebrides are extremely rich and contain a huge range of different plants and animals. However although the oceans cover about 70% of the Earth’s surface only 15% of the total number of species are represented in the marine environment and most of these are bottom dwellers. Of the 160,000 species of marine animals only 2% live in the open oceans. Amongst these open ocean dwelling animals are a range of marine mammals.

Mammals are animals belonging to the class Mammalia and they all breathe air through lungs and give birth to live young which they feed on milk produced from the mothers’ mammary glands. They are endotherms, maintaining their bodies at a constant temperature and they have skin with hairs. All these features are not really conducive to a marine life but there are 4 main groups or orders of marine mammals that have adapted very successfully to their underwater existence. One of these is the order of Cetaceans comprising the whales, dolphins and porpoises. To find out more about the cetaceans please click on the photo :

The other three orders represented in the marine environment are the Pinnipeds (the seals), the Sirenians (manatees and the dugong), and the Mustelidae which contains the otters (as well as badgers, weasels and skunks!) No Sirenians are found around Britain but there are two main species of seal: the common seal and the grey seal.

The Common Seal Phoca vitulina

The common seal is also known as the harbour seal since it is often found inshore, in estuaries and harbours.These are the smaller of the two species of seal seen in the Hebrides and they are easily distinguished from the grey seal by the shape of their noses. The common seal has a large head and large doleful eyes. The nostrils form a wide ‘V’ and their noses are more like a dog’s. They have a very variable coat colour ranging from a dark grey/brown on their backs to a pale creamy underside with spots and splotches. The pups are born with their adult markings. They moult their pale coats before they are born since they are born in the inter-tidal zone and must be able to swim almost immediately. Adult females can grow to 1.9m and the males are larger. They are often seen lying out on rocky headlands “sunbathing” with their tails and heads raised in a typical canoe shape, like large slugs. Mating takes place on the shore and they return to the same place every year. The females come into season in the summer, shortly after they have given birth so the birthing and mating seasons take place at one site and whilst the animals are all still in the area.

Common seals are noisy and communicate by calling to each other quite melodically. It has been found that their calls vary from area to area even around the British Isles.

The Grey Seal Halichoerus grypus

The grey seal, also known as the Atlantic seal, is the third rarest seal in the world and about half the world’s population of grey seals live in the waters around Britain. They are larger than the common seal, males growing to over 2.5 metres. Adult bulls are far heavier than the females and have very prominent arched “roman” noses. Breeding takes place in the spring after the pups are born. Once the fertilised ovum begins to develop it enters a stage of suspended development. This ensures that the birth and breeding seasons coincide.

Grey seals are found in many different colours, from creamy orange and brown to a dark grey, with irregular blotches all over. The pups are a pale creamy colour and like all seal pups they have soft fluffy fur. Being pale it provides some camouflage for them on the beach. They remain on the beach when their mothers go out to sea to find fish and if seen lying alone they should be left alone till she returns. The pups are suckled by their mothers for a relatively short time. The milk is very rich and the pups gain weight very quickly in order to prepare them for living in the cold sea water. Once they are weaned they eat fish and squid but they will also eat crustaceans and other small animals.

                   Grey Seal                                                                         Common Seal

Seals are particularly at risk from toxic pollutants ingested in their prey and which are accumulated in their fat. When they enter a period of fasting during the winter or the breeding season, they mobilise these fat reserves and chemicals such as PCB’s are released into their blood. These toxins affect their immune system and they become prone to diseases which it is though they would otherwise be able to fight. It is thought that this is one reason for the enormous seal fatalities which have occurred in recent years from influenza viruses. In 1988 more than 17,000 common seals died in the North Sea area due to PDV – phocine distemper virus.

If a seal is seen in distress or there is a pup which has been left on the beach for a whole day, do NOT approach it. Firstly if its mother can smell that you have been near the pup she will not return to feed it. Their sight is not very good and they rely on their excellent sense of smell to identify their young. They may be infected with a virus or bacterium which may be passed onto humans and they bite! If you are concerned about a seal please telephone the nearest marine mammal medic whose number can be obtained from directory enquiries or your local vet. They will come out and inspect the seal and if necessary they will remove it to a seal sanctuary.

Information about British Divers Marine Life Rescue can be found at www.bdmlr.org.uk

As with all marine mammals, seals are also often caught in fishing nest and lines. Their natural predators include sharks and orca as well as polar bears.

Otters Lutra lutra

Although otters can often be seen feeding and playing in the sea around the British Isles these are not sea otters but are river otters which have become adapted to a much more marine life. These river otters, which live mostly in the sea are found mainly around the Hebrides and the north west coast of Scotland and are often mistaken for true sea otters (Enhydra lutris). However there are no sea otters in European waters. The otters found in the Hebrides still need to return to fresh water every day to wash the salt out of their fur. Their ears are projecting and cupped unlike the sea otters’ and they have sleeker fur. Their feet have obvious footpads and their back paws are only slightly webbed. The tail is long and pointed and they are very agile both in and out of the water.

Otters are extremely playful and can be seen feeding and playing in the kelp along the shore or in streams running out to sea especially in the morning and evening. They pair up and remain together in territories occupying about 3 kilometres of shoreline. Their young are born in holts near the shore or along river banks. Most litters comprise 2 or 3 cubs and although they are weaned after about 14 weeks they stay with their mother for 13 to 15 months.

Otters have a double coat of hair which they shed throughout the year rather than moulting in a short moulting period. They have very acute senses of sight, smell and hearing and usually detect the presence of any humans long before you get to see them. In order to observe otters it is important to remain at a distance and be quiet and still.

Otters have a distinctive sweet smell and often mark their territory with scent and black spraints (droppings). Unlike other marine mammals the otters do not carry a thick layer of blubber and in order to maintain their body temperature they need to keep active and use up a lot of energy. This means they have to eat a large amount of food. Most river otters live on small fish but the otters around the Hebrides have become more like the sea otters in their diet. They are carnivorous and their main prey are crabs, shell fish such as clams and mussels and just about any type of small coastal animal.

To find out more about otters go to www.otter.org

Top of page