Seals Booklet 2 - Sea World

6
Pinnipeds
CHARACTERISTIC COMPARISON
OTARIIDS - Eared Seals
Fur seals and sea lions belong to the family Otariid or Otaridae which means "little ear". This
family is divided into two sub families of five species of sea lion and ten of fur seals. The fur
seals (Arctocephalinae) means "bear" "head". Examples of Otariids include New Zealand fur
seal (Arctocephalus forsteri), Australian fur seal (Arctocephalus pusillus doriferus),
Californian sea lion (Zalophus californianus) and Australian sea lion (Neophoca cinerea).
a.
b.
Figure 7: Two sub families of the Otariid; a. Australian sea lion ; b. New Zealand Fur seal
Distribution
The most important difference between eared seals and the others is that they are only found
in the sea and oceans. They often shelter in quiet bays, rocky, isolated islands and along sea
shores world wide.
Features
a. ear lobes
b. rear uneven claws
c. large front flippers
d. no hair on flippers
The sea lions have a rounded nose and short fur while the fur seals are more pointed in the
snout and have a thicker coat of fur. They feed on fish, crustaceans such as krill and lobsters
and an occasional penguin or other sea bird.
7
Pinnipeds
Locomotion and diving
While in the water the otariid moves its head from side to side in search of food. The rear
end of the body acts as a rudder. The front flippers are used as oars which makes the animal
'fly' along under water. Eared seals have been recorded to dive to about 118 metres but are
generally shallow feeders compared to the true seals.
They are quite agile on land. The hind flippers rotate forwards at the pelvis and the front
flippers extend to support the weight on the palms and soles. The belly is off the ground and
the hind flippers move alternately. As the animal moves more quickly it appears to be
galloping.
Breeding Behaviour
In many species, the breeding males come ashore late October to establish their territories.
Females arrive a few weeks later ready to give birth to pups from the previous years' mating.
90% of the pups are born before January. Active bulls may mate with over 100 females
during the breeding season but to keep his territory, he will not leave to eat. Most pups are
born between late spring and early summer which is often when food supply is richest. The
females always have four nipples. They are highly gregarious, especially during the breeding
season and thought to live up to 55 years of age.
8
Pinnipeds
ODOBENIDAE - Walruses
Distribution
There are only two species of walrus. One species is found in the North Pacific and the other
in the North Atlantic. Both live in the cold regions of the northern hemisphere where
temperatures may reach minus 35 Celsius. The walrus generally remain where the pack ice
is over the continental shelf.
Figure 8: The walrus
Features
These are the easiest of the pinnipeds to recognise.
a. They are larger than most other pinnipeds, with males growing to 3.5 metres and weighing
up to 1300 kgs and females weighing up to 650 kgs.
b. Tusks, which can grow to one metre in length, are used to help haul themselves out of the
water and around on land. They are also used as weapons when defending their territory.
c. Short whiskers help to find food such as clams and cockles, on the sea bed. They may
hunt for twelve hours each day in which time they eat up to 85 kgs.
d. There is very little hair on their body.
e. They spend two thirds of their life at sea, only hauling out onto land or pack ice to breed
and moult.
f. They are thought to live up to about 40 years of age.
Locomotion
They use both front and rear flippers to propel themselves through the water. Dives of ten
minutes have been observed when the animal has reached up to 90 metres.
Breeding Behaviour
Females may start breeding from four to ten years whereas the males do not mature till about
15 years when they reach a size adequate to compete for females. They mate in January/
February and will give birth to one calf in mid April to June of the next year, so pregnancy lasts
for nearly 16 months. The calf may weigh approximately 65 kgs and will feed on its mother's
milk for six months, after which its diet will be supplemented for a further 18 months till fully
weaned. The walrus has one of the lowest rates of reproduction of all mammals.
9
Pinnipeds
PHOCIDAE - Earless or True Seals
Distribution
There are nineteen species in two genera. They are the largest pinniped group and live in the
widest variety of places of all the pinniped family. Harbour seals usually frequent shallow
coastal waters and sandy beaches, but may travel hundreds of kilometres up rivers and into
lakes, especially when following a fish run.
Figure 9: The Harbour seal is a true seal and can be seen at Sea World
Features
a. no visible ears.
b. four flippers covered in fur
c. hind flippers cannot be rotated forward which means that they are less agile on land
compared to the eared seals.
d. nails on the hind flippers are the same size
e. skin is quite dark.
f. Feed mainly on fish and shell-fish
Locomotion
They propel themselves with the hind flippers, moving them from side to side, in a fish like
manner. When swimming quickly, the foreflippers are usually held close to the body until
changing direction. Some are able to dive to 600 metres for over an hour. On land, they
move clumsily. The hind flippers are not used but held clear of the ground which makes them
look like a 'caterpillar'. Surprisingly they can move very quickly if necessary and can cover
long distances over both flat and rocky ground.
Breeding
These animals come into season once the pup is weaned. The Hooded seal suckles for 12
days only whilst the Harbour seal suckles for 5 - 6 weeks. There is a 54% fat content in the
milk and no lactose. The female has either two or four nipples.