Phocidae

Phocinae

Harbour Seal:

The Harbour seal (Phoca vitulina), or the common seal is widely distributed in the North Atlantic. Some populations found in Canada live in freshwater throughout the year. Some Harbour seals have been spotted around the Portuguese coast which is very southern for this species. They mostly feed on fish such as herring and cod. They are also known to eat crustaceans and squid. The Harbour seal has the ability to descend to depths of up to 500m for 10 minutes but rarely does. Instead they commonly dive for short periods of time at around 20m depth.

The Harbour seal becomes sexually mature at between three and six years old. This species mates in the water between February and October. Females pick the strongest males to mate with; these males have usually been decided as a result of a fight which can take place in water or on land. The Harbour seal uses delayed implantation, including this, the gestation period lasts 11- 12 months. The period of birthing normally takes place between April to July but can differ depending on their location as it will be earlier in more southerly regions. After birth the mother is in charge of its pup, suckling it for around 25- 30 days before it is weaned. During this period the pup can almost double its birth weight which can be up to 10 kilograms. All pups are born fully developed and capable of swimming but most wait around a month before venturing into the sea.

Ringed Seal:

The Ringed seal (Pusa hispida) is a fairly small species of seal, growing up to 1.65m in length and weighing between 50 and 100 kilograms. As their name suggests, they have a dark coat with silver rings covering the back and side. They can be found in the North Atlantic (West and East Greenland) and the White Sea as well as an isolated population in the Baltic Sea. Ringed seals have a varied prey choice including fish such as herring and cod, small crustaceans and squid. When feeding they dive up to around 45m but they are able to reach much greater depths of a few hundred metres. The longest dive recorded for this species is 18 minutes, but like the Harbour seal it rarely dives for this length of time and to any great depths.

Ringed seal females become sexually mature at the age of four years old whereas males are seven years old. The mating period is in the spring and including delayed implantation, gestation is 11 months. The Ringed seals create holes or lairs in the ice and snow using the claws in their fore flippers. Once made, the seals maintain their caves as it acts as protection from predators as well as shelter for themselves and their young. It has been seen that the mortality rate in pups born on the surface ice, without shelter is very high. This species normally gives birth in March to April. As with all Pinniped species, the female takes care of its pup for around six weeks (a long time compared to a lot of other seals). During the time leading up to weaning, the pup is able to increase its body mass four times, sometimes more. Ringed seals are very active as pups; they spend 50% of their time in the water and are able to dive to depths of 90m, remaining underwater for more than 10 minute periods.

Monachinae

Mediterranean Monk Seal:

The Mediterranean Monk (Monachus monachus) seal is one of the most endangered mammals (second to the Saimma Ringed Seal). They are a relatively large species of seal, growing up to 2.8m in length and weighing up to 400 kilograms. They have small foreflippers in comparison to their large body size. Before a mystery disease hit the Mauritania colony in 1997 killing about two thirds of the colony, the Mediterranean Monk seal was widespread in the Mediterranean. Now it is only found in small populations in the Adriatic Sea, the Black Sea and the Aegean Sea on the North African coast as well as off the Mauritanian and West African Coast. Mediterranean Monk Seals have a very similar diet to the rest of the true seals as they feed on fish, squid, octopus and eels. They have been observed diving at depths of 500m but usually feed at much shallower depths of 30m.

Relatively little is known about the reproduction of the Mediterranean Monk Seal. Females and males reach sexual maturity at the age of four to six years old and at a length of 2.1m. There does not appear to be a set breeding season as mating and births occur all year round with a peak between August and October. The gestation rate within this species is estimated to be 11-12 months like most other seals. They typically give birth and nurse their pups in undersea caves. Because of this the pup mortality rate is extremely high as high surf or storms wash the caves out.

Northern Elephant Seal:

The Northern Elephant (Mirounga angustirostris) seal can be found off the coast of Mexico and Southern California. Generally they do not migrate but during the spring few males are found on the beaches and it is thought that they have gone far out to sea. They are very similar to the Southern elephant seal in appearance apart from the proboscis. In the Northern Elephant seal it is very long and hangs down when relaxed. When erect it curves down between the jaws and directs the nostrils towards the pharynx. This means that the mouth is able to act as a resonating chamber as snorts made by the seal are directed down into the pharynx. Unlike many other seals, elephant seals generally feed at depths greater than 200m, sometimes up to 800m. At this depth visibility is less and it has been thought that they use their vibration sensitive vibrissae to help capture prey. They feed on a range of different food such as deep water squid, sharks and rays. Their food source also acts as their water source. It has been observed that males and females have different feeding behaviours, males, unlike females return to the same feeding place each year.

Difference between males and females. © http://www.flickr.com/photos/marlinharms
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Males gather at the breeding site around two weeks before the females in December to January. They use this time to gain their territory. There are many fights between the bulls to determine which of the strongest ones will have a harem. These fights start out with the males roaring which indicates its size, sometimes that is enough if not a brutal fight occurs which often leads to bloodshed. Many younger unsuccessful males will remain on the edges of the harems hoping to get females or occasionally challenge the harem bull. Harems are usually between 20 and 40 but have been to known to be as many as 100 seals. Females are divided into harems as soon as they get to the beach and have their pups the following week. To break the umbilical cord the females move their hind quarters swiftly. Male Northern Elephant seals remain on the beach for the next two months until the breeding season is over whereas females stay for an extra month, without going to sea to feed, nursing their pups. During their time on the beach, the males offer no form of parental care, if anything they are a danger to the pups as they often squash the pups by rolling on them.