|
Wildlife of Tasmania
Mammals of Tasmania
Seals
Juvenile elephant seal
 |
Thirty five species of seal inhabit the oceans of the world. They are found throughout the marine environment, from icy polar waters to the warm waters of the tropics. Much like whales and dolphins, seals are adapted to the marine environment with a streamlined body, limbs modified into flippers and a layer of blubber for insulation. They also have a specialised circulatory system that allows them to sustain prolonged dives while feeding. However, unlike whales and dolphins, seals are not confined to the water but regularly come out of the water (haul-out) to rest, mate, moult and give birth.
See our pages on living with seals and seal viewing guidelines.
A number of species occasionally visit our shores, however only two species breed in Tasmanian waters.
The seals that breed in Tasmania are the:
Other seals that may be seen, or have been recorded, in Tasmania are:
Types of seals
Seals belong to the Order Pinnipedia. Pinnipeds are classified into three families:
- fur seals and sea lions (family Otariidae)
- the walrus (family Obdobenidae)
- 'true' seals (family Phocidae)
Otarid seals, also called 'eared' seals, include sea lions and fur seals.
They have obvious external ears and large foreflippers which can be turned
forward. They are able to bring their hindflippers underneath the body in
order to walk or run, albeit somewhat awkwardly. Having flippers that bend
forward also enables the otarid seal to "sit up" and lift its upper body
from the ground and remain stable in this position. Fur seals have a well
developed coat made up of long, coarse guard hairs overlying a thick, woolly
underfur that traps a layer of air and insulates the animal. Sea lions have
thinner coats than fur seals which is better suited to the warmer climates
they inhabit.
Unlike Otarid seals, Phocid seals have no external ears or 'pinna'. Phocid seals are not as manouverable. The flippers of the phocid seal
extend behind the body and cannot be brought forward in order to walk. They
raise themselves briefly from the ground but cannot maintain a sitting
position like the Otarid seals. Instead, the Phocid seals are limited to
crawling and wriggling, using their foreflippers for traction and
propulsion. The Phocid seal has a thinner coat , made of short, stiff guard
hairs, overlying a thin but dense layer of wooly underfur which does not
actaully trap air, but instead becomes wetted to the skin when the animal
is in the water. In the absence of a thick coat, the
Phocids have a thick blubber layer which provides most of the animal's
insulation.
Foraging
While at sea, seals alternate between resting on the surface and foraging for food. Although the diet varies between species, seals generally eat fish, squid, octopus and crustaceans such as krill. When foraging, seals can leave haulout sites for days, weeks or in the case of elephant seals -- months. They may also travel vast distances and swim to great depths in search of prey. Southern elephant seals, which feed in the cold sub-antarctic waters, can dive to 1800 m for half an hour or more! Marine mammals have
many adaptations which enable them to dive to such depths and to
avoid the 'bends' when resurfacing after dives.
Reproduction
Seals give birth to live young and suckle them from mammary glands just as humans do. Normally only one pup is born but twins can occur. Pregnancy in seals ranges from 6 weeks to 9 months depending on the species. However, all species are capable of suspending the development of the embryo so that births can occur at the desired time of the year.
Recovering from the slaughter
In Australia the commercial harvest of seals for the fur trade began in 1798.
The industry had collapsed by the 1830s, and although it was still legal to
hunt seals until 1923, this rarely occurred.
Four species of seal once bred in Tasmania's Bass Strait, the Australian
fur seal, New Zealand fur seal, Australian sea lion, and the Southern
Elephant seal.
Three of these species were totally eradicated and only the Australian fur
seal now remains in Bass Strait. Approximately 17 000 pups are born each
year at both Tasmanian and Victorian breeding colonies and the total
Australian fur seal population is estimated to be 60 000 to 80 000. Prior
to the exploitation of the sealing industry there was an estimated 3/4 of a
million seals in Bass Strait.
The New Zealand fur seal is now restricted to breeding on a small group of
islands off the South coast of Tasmania, the Maatsuyker Island group, where
approximately 100 pups are born each year. The New Zealand fur seal is now
classified as a threatened species in Tasmania. Although this species no
longer breeds in Bass Strait the New Zealand fur seal breeds in South
Australia and Western Australia and has a total population of approximately
35 000.
Threats to seals
Entanglement in marine debris
is a constant threat to seals
 |
The greatest threat to seals comes not from their natural predators, white pointer sharks and killer whales, but from humans. Seals are shot by fishermen, and caught and killed as 'accidental by-catch' in
fisheries operations such as trawling and gill netting, while the ingestion
of waste oil and other liquid pollutants poses a further threat to seals.
Seals also suffer horrific deaths due to marine pollution, such as entanglement in marine debris. This plastic, non-biodegradable debris includes free-drifting trawl net, packaging straps and monofilament gill net. Such debris causes 2% of Tasmania's seals to suffer a slow strangulation.
Seals are among the most inquisitive of creatures and often end up with rope, fishing net or packaging strap wrapped around their necks. As the seal grows, this material gradually strangles the animal. Before the seal dies it may suffer from starvation due to the entanglement restricting movement or preventing the swallowing of food. Entanglements cutting through the skin, blubber and muscle to reveal the esophagus have been observed in Tasmanian waters. Ultimately, death is slow and very painful!
Beached seals
Seals do not 'strand' in the true sense of the word as they are adapted to spending some time on land and are quite capable of movement on land. Seals are regularly found lying or 'hauled out' on the Tasmanian
coastline. All species found in Tasmania engage in this behaviour.
Sick or injured seals, however, also may be found on the beach.
Consequently, it is not unusual for people to come across seals. Should you be fortunate enough to come across a seal, it is very important for both the seal's sake and your own safety not to disturb the animal in any way.
See our pages on observing seals in the wild for further details.
All seals are wholly protected throughout Australian waters.
Research
Tasmanian seal and cetacean research is largely funded by the legacy of Hobart born
woman, Pauline Curran, who in 1926 married Prince Maximilian Melikoff of the exiled Russian royal family. Princess Melikoff died in 1988, and in her will, bequeathed a trust to help save our seals and dolphins.
Branding and tagging help us to identify individual seals and to learn how long
they live and how far they range. Branding and tagging was conducted at Bass Strait breeding colonies and the Maatsuyker Island
group from 1990 to 1997. Australian fur seals branded and/ or tagged at
Bass Strait colonies are often observed at haul- outs on islands south of Tasmania. A New Zealand fur seal tagged as a pup on Maatsuyker Island in 1994 (tag
no. 239) was observed 13 months later on Macquarie Island - half way to
Antarctica.
Tracking seals has uncovered some surprising facts - for example, using dive
recorders, a male Australian fur seal, captured at Port Arthur and released at the north of Tasmania was tracked over ten days, covering more than 500 km and diving
nearly 500 times each day. The deepest dive was 102 m, and the longest lasted
seven minutes.
Six Australian fur seal cows from Tenth Island have been equipped with satellite-
linked- time- depth recorders and results show that cow seals forage mostly within
200 km of the breeding colony. Dive information from one of these seals revealed
that her dives, mostly at night, lasted about three minutes each and took her to
depths below 45 m.
Research is presently being carried out on Australian fur seals from Victorian breeding colonies. This research shows that this species travels across great distances, and frequently forages in Tasmanian waters. For information on the progress of these seals, visit the research pages provided by the Phillip Island Nature Park Web Site.
Research like this tells us more about seal behaviour, and helps us to better
understand their place in the marine environment.
What you can do to help
The following information is sought by researchers to help our understanding
and management of seals in Tasmania. Any information should be passed on to the
Nature Conservation Branch (Phone (03) 6233 6556)
Sightings of any seal, whether healthy, sick or dead, should be reported. The
Marine Unit is collating data on all seal sightings in Tasmania. Whether you
think we'd be interested or not, give us a call anyway!
The Parks and Wildlife Service is also keen to recieve sightings of:
- entangled seals. It would be of great benefit if the type and colour of the material is recorded.
- shark bites. Seals are often seen with shark bites and information is needed on the position of the bite, approximate size and whether it is fresh or a scar etc.
- tags or freeze brands.
- masses of dead or dying cuttlefish and squid at the surface. As an important prey item for Australian fur seals the knowledge of such die-offs is important for research.
Further Information
Seal Conservation Society
A British-based Web Site with information on species of seals and conservation issues.
[Wildlife of Tasmania] [Tasmanian Mammals]
|
