Seals of Ireland
Seals are beautiful, unique, semi-aquatic marine mammals that breathe air, and share their time between land and sea. They belong to a group of mammals called Pinnipeds, which translates to ‘wing-footed’ in Latin, referring to their paddle like flippers. Worldwide, there are 33 species of Pinnipeds, two of which are native to Ireland: the Common Seal and the Grey Seal.
Pinnipeds can be grouped into three categories: True Seals (Phocids), Eared Seals (Otariids) or Walruses (Odobenids). Both the Grey and Common seals are known as True seals, as they lack an external ear, and simply have an opening on either side of the head. True seals are also slow and clumsy on land, using their bodies to bounce along the ground, whereas eared seals have a rotating pelvis which enables them to “walk” more easily on land, same as the walrus. Walrus are the only remaining members of the Odobenids and are easily recognised by their characteristic tusks.
Californian Sea lion
New Zealand Fur Seal
ADAPTATIONS TO LIFE IN THE SEA
Keeping Warm: Seals, like all mammals, are warm blooded. A smooth, thick layer of blubber lies underneath the skin to regulate the body temperature and keep them warm, even in icy ocean water. Seals are also covered with a short, dense fur to help keep them warm.
As seals are so well designed to retain heat, on warm days you may see them fanning out their flippers, which lack insulating blubber, to cool down. On land, they can often be seen flipping damp sand onto their backs in an attempt to keep cool. Also dilation of the arterioles, particularly in the flippers, allows a rush of blood to the skin promoting cooling.
Streamlining: ‘True seals’ have specialised bodies shaped like torpedoes, with no obvious neck, no external ears or genitalia, and reduced limbs and tail allowing them to swim and manoeuvre quickly in water to escape predators or catch prey. This body shape helps to reduce drag in the water which is 800 times denser than air. The streamlining is enhanced by the layer of blubber rounding off all bony protuberances.
Locomotion: Seal are often referred to as the ‘acrobats of the sea’ due to their agility in water. They are able to swim effectively over very long distances achieving speeds of up to 25 knots! Their front flippers are used primarily for steering, while their hind flippers used for propulsion, are bound to the pelvis in such a way that they cannot bring them under their body to walk on them like fur seals or sea lions. However, as agile as they are under water, they are very clumsy on land, having to bounce and wriggle with their front flippers and abdominal muscles. This makes them slow to escape and vulnerable on land.
- It is believed that seals probably evolved from otter like ancestors Puijila darwini about 15-20 million years ago.
- Their closest land dwelling relatives are said to be bears, dogs and weasels. Can you spot the similarities?
- Since seals are closely related to dogs, there have been records of zoonotic disease transferring from one to the other. This is another important reason to keep dogs on a lead and far from seals resting on beaches!
Grey and Common seals live scattered along our coastline. Grey seals like to roam around the North Atlantic during the year, travelling from one country to another, but returning to the same place each year to breed and give birth. They are found on offshore islands and on rocky beaches and coves. Common seals travel far less, and can usually be seen in bays, estuaries and sheltered inlets. As they must spend large amounts of time on land resting and restoring energy reserves between swims, it is important for both species to have access to safe haul-out sites where they are protected from disturbance from humans and dogs.
Seals feed underwater, hunting for their prey using sight, sound, and vibrations, picked up by sensitive whiskers called “Vibrissae”. Their eyes are very well adapted for low light levels underwater, and they also have well developed directional hearing.
Their teeth are sharp, like that of a typical carnivore, with incisors and canines for ripping and shredding, but they also have backwards pointing teeth used to hold onto slippery prey.
As opportunistic feeders, seals feed on whatever they can find including shoaling fish like mackerel and herring, as well as crustaceans, squid, octopus and sand eels. Because they feed on such a wide variety of prey, they can often mistake non-edible items such as soft plastics as food items, which can be very dangerous to them if ingested.
Diving: Dives usually last 5 – 15 minutes and from 30 – 70 metres. The nostrils are kept closed during dives and opened on surfacing. Only a very short recovery period is needed between dives. Seals exhale on diving and the lungs and alveoli collapse at a depth between 25 – 50 metres, thus pushing any residual air into non-absorptive air spaces. This prevents seals from suffering from buoyancy problems and any risk of the bends.
Coping with Salt: Seals restrict their seawater intake to avoid taking on excess salt. They primarily derive fluids from the food they consume, e.g. 90% of fresh water taken in by common seals is from the fish they eat and most of the remaining 10% is metabolic water and inspired water vapour. Seals kidneys are very efficient at concentrating urine. They produce urine that has a higher concentration of salt than seawater.
Vision: The eyes are large with a strengthened cornea adapted to the refractive index of water, and a retina adapted to dim light conditions, allowing good visibility underwater. They also have a protective third eyelid that wipes sand away and a continually produced tear film also helps to protect the eyes. On land, in brightly lit conditions, constriction of the pupil reduces light intensity, which in turn reduces the refraction of light through the lens, allowing the eye to effectively focus.
Grey Seal Quickfacts:
- Scientific name: Halichoerus grypus (meaning ‘Hook Nosed Sea Pig’)
- Grey Seals have a longer pupping season in Ireland; we have seen pups as early as August, however normally they pup between the winter months of October and February.
- Pups are born at around 2.5 – 3.5ft (90-105cm) in length and weigh between 12 -16kg.
- They are born with a fluffy, white coat of baby fur (lanugo), and must stay on the beach for their first 3 weeks of life as they are not yet strong swimmers. Seals produce milk with the highest fat content in the animal kingdom at 50%. While feeding from their mother’s fat rich milk, the pups triple in weight and are then rapidly weaned at around 3 weeks of age which coincides with them moulting their white coat.
- Once weaned, pups are left to fend for themselves, and finally take to the water to learn how to hunt fish on their own. Grey seal pups have an extremely high mortality rate of up to 40% of pups dying depending on the season.
- Adult males reach over 2 metres (6.5 – 8 feet) in length and can weigh over 310kg. Males have a shorter life expectancy than females at 25 years.
- Adult females are significantly smaller than males at 1.8 metres (over 5.5 feet) in length and weigh on average 155kg. Female Grey seals live longer than males at around 35 years.
- Grey seals are a Protected Species in Ireland Under the Irish Wildlife Act, 1976 and The EU’s Marine Mammal Protection Act, 1972. They almost went extinct in Ireland in the early 1900’s due to hunting, but these protections have allowed their numbers to start to recover.
- It is estimated that there is currently a stable population of around 5,000 Grey Seals in Irish waters, and a world-wide population of approximately 300,000, which is fewer than African Elephants.
Common/Harbor Seal Quickfacts:
- Scientific Name: Phoca vitulina (also referred to as ‘Harbour seals’ in other parts of the world).
- Common seals generally start having their pups in the summer months of June and July, however we sometimes see early pups in May and then stragglers in August and September.
- Pups at birth are very small at only 2 -3 feet (65-100cm) in length and weigh between 6-12kg.
- They are born ready to swim with their waterproof adult coat, having moulted their lanugo fur in utero. Sometimes, however, if a pup is born prematurely they may still have their lanugo present. They recover quickly after birth and after their first suckle take to the water with their mother and can swim and dive straight away.
- They are weaned between 4 – 6 weeks of age, and have been known to stay with their mothers for weeks afterward to learn how to hunt and other survival skills.
- Adult males reach up to 6.5 feet (1.9metres) in length and weigh up to 150kg. Males have a shorter life span of up to 25 years.
- Adult females are slightly smaller reaching 5.5 feet (1.7metres) in length and up to 100kg. Females have a longer life span of up to 35 years.
- Common seals are a Protected Species in Ireland Under the Irish Wildlife Act, 1976 and The EU’s Marine Mammal Protection Act, 1972. They are considered a species of special concern in Ireland as their numbers have been slowly declining, with only approximately 2,500 remaining.
- The name ‘Common’ comes from this species having the most wide ranging populations, with an estimated 350,000 – 500,000 animals world-wide.