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| Introduction |
The Australian Fur Seals and Sea Lions
are eared seals that are able to use their hind flippers to walk on land.
The fur-seal has a dense under-fur below a sleek outer covering of guard
hairs and is the more abundant species, with an estimated 20,000 to 25,000
found in Bass Strait and the adjacent coastal waters of Tasmania and
southern New South Wales. In contrast, the sea-lion lacks under-fur and
the population of 3,000 to 5,000 mainly inhabits offshore islands, from
Houtman Abrolhos in Western Australia to Kangaroo Island and at Point Le
Batt on the mainland at South Australia.
In the early 1 800s these beautiful mammals were slaughtered for their fur
and the population was dramatically reduced. Sealing persisted until
protective legislation was passed in Victoria in 1891, although it still
went on under regulation in Tasmania until at least 1923.
The breeding season for the Fur Seal starts in late October, when the
large bulls arrive at the colony. Size and strength are important
advantages during the intense competition for access to the females and
the males fight ferociously. The female is much smaller than the male,
which has a massive neck and shoulders when fully developed, along with
powerful canine teeth. Harems are not formed and the females and immature
males are allowed to move freely between the territories. Usually only one
pup is born and five or six days after the birth the cow mates again and
goes to sea to feed, returning two to five days later to resume suckling
her pup. This pattern continues for about eight months by which time the
pup is able to accompany her to sea and take solid food. Weaning is at the
age of ten to eleven months.
When on shore the Fur Seal is sensitive to heat and avoids stress by
moving into the shade or tide pools. To move on land it uses its four
flippers in different gaits from a low shambling walk to a fast gallop.
Diet consists of fish, squid, octopus and rock lobsters, with large prey
being broken up by vigorous shaking.
The Sea Lion is a relatively sedentary animal. It comes ashore on sandy
beaches but uses rocky areas for breeding. The breeding season is variable
and seems to be in 18 month intervals rather than an annual cycle.
Both males and females are strongly territorial during breeding season.
The aggression is even directed towards young pups which contributes
significantly to their mortality rate. A strong bond is held between the
female and her pup and this lasts for some time after it has been weaned
at the age of more than a year. Little is known of their diet, although
squid beaks have been found in the stomachs of dead animals. |
|
|
- STREWN with mud-caked bodies, the tidal flats
looked like a battlefield. Five days previously, tropical cyclone Kathy
had torn through the western Gulf of Carpentaria region, leaving a trail
of devastation. The storm surge accompanying the 1984 cyclone had been
awesome. Here, some 35 kilometres north-east of Borroloola, it had
dumped hundreds of sea creatures on the mudflats near the mouth of the
McArthur River and for five long days turtles, sharks, rays, fish and
dugongs had gradually succumbed to the tropical sun. The helicopter that
had flown me from Borroloola put down gingerly on the flats 50 metres
from three young dugongs I'd spotted from the air. They thrashed about
at the clatter and roar of the engine, frantically pounding their tails
and spinning on their long axes - the same panic reaction that can cause
them to tangle in fishing nets and drown. (See
Pictures Here)
|
- Bill Freeland, of the Conservation Commission of
the Northern Territory, and I stepped out and struggled through the
thick grey mud towards the dugongs. Each had carved out a small wallow
and lay there eyeing us, quiet now, as we approached. They were among 27
we found scattered over some 275 square kilometres and up to 9 km inland
- some behind stands of 3 m tall mangroves - during a two-day search.
There was still a lot of water around. Like the three youngsters, most
lay in wallows up to 3 m wide and 30 centimetres deep. Although created
inadvertently by panic-stricken thrashing, these wallows probably saved
their occupants from death by dehydration. We had intended to make this
a reconnaissance mission: I was there to recover information from dead
dugongs, the marine mammals I had been researching for 10 years at
Townsville's James Cook University. However, to our amazement only two
of them were dead. So our mission quickly became one of rescue. With
great difficulty, we muscled each dugong onto a cargo net; I received a
spectacular black eye from the tail fluke of one large female. Although
the net was fine for the young dugongs, it was barely adequate for
adults measuring up to 2.9 m long and weighing close to 400 kilograms.
Once cocooned in the net, each was airlifted to the nearest waterway and
released. Two died in transit, probably from shock, but most swam off
strongly to rejoin their fellows in the gulf.
These tropical waters are home to one of the world's largest dugong
populations. Aborigines of the northern coastal communities and Torres
Strait Islanders have had a long and intimate association with them, as
have many other indigenous people of the Indian and western Pacific
oceans. But despite its large numbers, the dugong remains a mystery to
most Australians. To confuse things further, this shy creature has for
thousands of years been linked with the mermaid myth. Warm-blooded,
fleshy and equipped with the archetypal mermaid tail, the dugong seen
from a distance is said to have set many a love-starved sailor's heart
pounding. (See Pictures Here)
|
- Encrusted in mud, this dugong was among 27 found
stranded on mudflats at the mouth of the NT's McArthur River about a
week after cyclone Kathy in 1984. All but two were alive, and were
probably saved from fatal dehydration by their cocoons of mud or the
wallows they inadvertently dug as they thrashed around in panic.
Residents of nearby Borroloola stopped their own clean-up to help rescue
them. Bill Freeland of the Conservation
Commission of the Northern Territory and author Helene Marsh measure and
sex a dugong in a wallow. Shortly afterwards it was airlifted (below) to
the nearest tidal creek in a helicopter cargo net. (See
Pictures Here)
|
- In recent years scientists have learnt much about
the biology of the gentle dugong, and with this knowledge has come a
concern for its welfare. Native to the seas of 42 countries, from east
Africa across to Vanuatu in the Pacific, it is, despite its extensive
range, rare throughout much of it these days, and in some areas even
endangered. As a lecturer at James Cook University, a dugong researcher
for 15 years and an adviser to the Great Barrier Reef Marine Park
Authority, I find the welfare of the dugong is an issue that's never far
near the top of his head, enabling him to breathe while most of his body
was under water. His pig-like head had a large horseshoe-shaped upper
lip covered with stout bristles. Inside his mouth were horny
pads like the one a cow uses for grasping grass. The skin on his back
was nearly 3.5 cm thick. This included fat, which was thinner than that
of most marine mammals I'd examined. Except
for the bristles on his muzzle, the hair on his body was short and
sparse. As I ran my hand over his back, conflicting images filled my
head. How, I wondered, could anyone mistake such a creature for a
mermaid, even at a distance? "Sea cow", its common name, describes it
well; "Sirenia", the group's scientific name, derived from the Latin for
siren, definitely does not! At that time, the university's research
project involved studying dugongs killed locally in shark nets, which
claimed 249 between 1964 and 1983. Our knowledge of the species' biology
was so scant that any information we could collect would be important.
Most accidental drownings – and sightings - of dugongs occur in water
less than 5 m deep in bays, shallows and reef areas protected from
strong wind and heavy seas and with extensive beds of seagrass.
(See Pictures Here)
|
- Mermaids have fascinated people from ancient
times to the present day. The one above featured in a 1989 Walt Disney
production, THE LITTLE MERMAID, based on a Han Christian Andersen tale.
Mermaids were said to attract sailors with their beauty and singing but
were a bad omen. Mermaid legends may have arisen when mariners glimpsed
sea cows, with their rounded bodies and swollen mammary glands. The
manatee's tail (below) is similar to a beaver's while the distinctive
fluked tail (inset) of the dugong is consistent with its more
streamlined shape. as deep as 37 m, and sometimes in creeks and
rivers. Although generally considered rather slow swimmers, dugongs can
reach 20 km/h over short distances. They can also cover long distances:
one of my study animals travelled 200 km in two days. They usually spend
only seconds breathing at the surface between dives that average around
1-2 minutes. The longest dive recorded was over eight minutes; the
deepest more than 20 m. TO some people, dugongs (the word is of Malay
origin and gives the species its scientific name Dugong dugon] sue
sacred, to others a source of meat, oil, fine leather and even ivory.
Dugongs were sighted, but misidentified, by some of our earliest
explorers. In 1688, William Dampier reported "manatees" in a bay on the
north coast of WA, and, in 1789, while exploring Moreton Bay, Matthew
Flinders saw several large "fish or animals that came to the surface to
breathe in the manner of a porpoise or rather seal, for they did not
spout, nor had they any dorsal fin". Dugongs may look rather like rotund
dolphins, or even seals, but the resemblance is deceptive. They (and
their manatee cousins) are in fact more closely related to elephants.
Like elephants, they are plant-eaters, feeding almost exclusively on
seagrasses, which are broken down by bacteria in their large intestine.
In an adult dugong this is as thick as a fire hose and about 30 m long.
(See Pictures Here)
|
- Biological research is a bit like detective work.
By studying a trail of clues, we can reconstruct the subject's life
history. For example, tusks can reveal age, and scars on the uterus can
show how many calves a female has had. Dugongs may live for 70 years or
more. The female doesn't have her first calf until she is at least 10
years old; then she bears a single calf every 3-5 years after a
gestation period of about 13 months. The newbornrn
calf is just over a metre long and weighs around 30 kg. Although it
starts eating seagrass soon after birth, it continues to nurse from
human-like nipples near the base of its mother's flippers until up to 18
months old. A tale of
two skulls... The enormous size of Stellei's sea cow can be gauged when
its skull is seen beside one from an adult dugong. American
palaeontologist Daryl Damning, a specialist in
sirenian fossils, inspects the skulls at the Smithsonian Institution in
Washington, DC, one of the world's few museums that possess skulls of
this extinct giant. Stellei's sea cow lived on kelp and was so adapted
to feeding in shallow water that it was unable to dive, making it easy
prey for hunters. Australia lack marine sediments from the appropriate
geological age and no sirenian fossils have been found here.
(See Pictures Here)
|
- By collating the layers in this dugong tusk
(below), Helene Marsh finds that the adult female from which it came was
22 years old. The layers are deposited like a tree's growth rings, one
dark layer and one light layer representing one year. The tusk was cut
in half with a rock saw and etched with acid to highlight the layering.
Tusk ends are fashioned into cigarette holders on Indonesia's Aru
Islands. An orphaned female a few months
old that was brought to an oceanarium in, Cairns for hand-rearing
shortly after being accidentally netted. Like all dugong calves, she was
very affectionate and really seemed to enjoy being cuddled while being
bottle-fed. She always tended to be more enthusiastic about this than
the person doing the cuddling, perhaps because dugong skin feels a lot
like sandpaper! Sadly, Dolly died four months later of an infection
contracted from sewage-contaminated seagrass. Dugongs do not fare well
in cap-tivity. Of 30 kept in 13 institutions worldwide since 1959, nine
died within a month and only 11 lived longer than six months. The
longest surviving were a pair kept in southern India for 11 years. They
were hand-fed a total of 40 kg of seagrass a day, which was clearly not
enough, as they failed to grow normally. During their captivity, several
accounts were published of their mating behaviour, but when they died,
both were found to be male! I know of only four in captivity at present:
two in Japan's Toba Aquarium, and two in Indonesia's Jaya Ancol
Aquarium. Putting their life history through a computer, it's not hard
to see why dugongs are vulnerable to extinction. Even if every female
had a calf every three years from the age of 10, the Mermaids have
fascinated people from ancient times to the present day. The one above
featured in a 1989 Walt Disney production, THE LITTLE MERMAID, based on
a Hans Christian Andersen tale. Mermaids were said to attract sailors
with their beauty and singing but were a bad omen. Mermaid legends may
have arisen when mariners glimpsed sea cows, with their rounded bodies
and swollen mammary glands. The manatee's tail (below) is similar to a
beaver's while the distinctive fluked tail (inset) of the dugong is
consistent with its more streamlined shape. as deep as 37m, and
sometimes in creeks and rivers. (See
Pictures Here)
|
- Although generally considered rather slow
swimmers, dugongs can reach 20 km/h over short distances. They can also
cover long distances: one of my study animals travelled 200 km in two
days. They usually spend only seconds breathing at the surface between
dives that average around 1-2 minutes. The longest dive recorded was
over eight minutes; the deepest more than 20 m. TO some people, dugongs
(the word is of Malay origin and gives the species its scientific name
Dugong dugon) are sacred, to others a source of meat, oil, fine leather
and even ivory. Dugongs were sighted, but misidentified, by some of our
earliest explorers. In 1688, William Dampier reported "manatees" in a
bay on the north coast of Western Australia,
and, in 1789, while exploring Moreton Bay, Matthew Flinders saw several
large "fish animals that came to the surface to breathe in the manner of
a porpoise or rather seal, for they did not spout, nor had they any
dorsal fin". Dugongs may look rather like rotund dolphins, or even
seals, but the resemblance is deceptive. They (and their manatee
cousins) are in fact more closely related to elephants. Like elephants,
they are plant-eaters, feeding almost exclusively on sea-grasses, which
are broken down by bacteria in their large intestine. In an adult dugong
this is as thick as a fire hose and about 30 m long. Biological research
is a bit like detective work. By studying a trail of clues, we can
reconstruct the subject's life history. For example, tusks can reveal
age, and scars on the uterus can show how many calves a female has had.
Dugongs may live for 70 years or more. The female doesn't have her first
calf until she is at least 10 years old; then she bears a single calf
every 3-5 years after a gestation period of about 13 months. The newborn
calf is just over a metre long and weighs around 30 kg. Although it
starts eating seagrass soon after birth, it 'continues to nurse from
human-like nipples near the base of its mother's flippers until up to 18
months old. (See Pictures
Here)
|
- The population would be unlikely to increase at
more than about 5 per cent a year. Thus, if an area has 200 dugongs, no
more than five females a year can be killed by humans if that population
is to remain stable. MOST Aborigines and
Torres Strait Islanders are legally allowed to hunt dugongs in
Australian waters. To them the dugong is often more than just an
important food source; it is central to their culture, economy and even
religion. Hunting it is an expression of their Aboriginality - tangible
evidence of their skill, knowledge and oneness with the elements of
their environment. As part of my work I have
been on many dugong hunts with the people of Cape 'York and Torres
Strait, a rare privilege in cultures where hunting tends to be a
male-only activity. Traditionally, dugong
hunters use spears with detachable barbed heads. Before European
contact, they either perched on temporary platforms over seagrass or
scouted the reef waters in canoes. When a dugong came up to breathe, the
harpooner hurled himself at it. If he made a successful strike, there
would often be a furious ride until the dugong tired itself out. Then
the hunter would hold it under until it drowned. Today the aluminium
dinghy and outboard motor have all but replaced the bark canoe and the
paddle. (See Pictures Here)
|
- When the new technology
reached the people of northern Torres Strait, the dugong catch went up -
then plummeted. I estimate that in the late 1970s between 500 and 1000
were caught annually in Torres Strait. Computer calculations show there
would have to be at least 22,000 dugongs there to sustain an annual
harvest of 500, or 44,000 for a harvest of 1000. I am sure there weren't
as many as that. The number of Torres Strait dugongs sold in the Daru
market in southern Papua New Guinea dropped from 218 in 1979 to just 18
in the first eight months of 1982. Thereafter both the sale of dugong
and records of catches ceased. Sales of dugong Family portrait
(below)... William Bilsborough, centre, and his family pose with their
dugong catch in Hervey Bay, (Burrum Heads) Queensland, in the 1930s.
Bilsborough supplied dugong oil to pharmacies for use in medicines and
face cream. A dugong yields some 20 litres of oil.
|
- All the dugong hunting I have watched has been
done in dinghies fitted with outboard motors. After the dugong is
killed, it is usually towed to a nearby beach for butchering. There I
take measurements and remove specimens, which always mystifies and
amuses the hunters. For them, the rewards for success are great, in
terms of both food and status. An average adult dugong yields about 100
to 150 kg of meat that tastes rather like pork or veal.
Some mainland coastal Aboriginal communities have turned to
hunting
wild cattle, buffalo and pigs, taking the pressure off dugongs. As a
result the number of dugongs caught in 1984-87 by the Hopevale and
Lock-hart River Aboriginal communities on the east coast of Cape York
Peninsula was much lower than what I estimate could be sustained.
Other Aboriginal communities in northern Cape York Peninsula have
never hunted dugongs, considering dugong meat inferior and that eating
it brings misfortune. (See
Pictures Here)
|
- Since June 1988, Tony has been studying dugongs
in Moreton Bay, where more than 500 graze within 25 km of Brisbane's
waterfront suburbs. The bay's dugongs were believed to have been wiped
out by a cottage industry that exploited their oil from the mid-1800s to
around the 1940s. Dugong oil was thought to cure everything from
tuberculosis to joint pains. For decades marine biologists working in
the area had never seen a dugong there. Then, during an aerial survey in
May 1976, George Hein-sohn could not believe his eyes when he spotted a
herd of some 200. Dugong mothers are very attentive, communicating with their young
through bird-like chirps and high-pitched squeaks and squeals. The calf
never ventures far from its mother and frequently rides on her back.
Mothers appear highly protective. A report from Torres Strait told of
one sacrificing her life to save her calf from a shark, luring the
predator into increasingly shallow water until both she and it became
grounded. This did not stop the shark from
fatally mauling her, but the calf fled to safety.
The dugong's often intriguing behaviour has also been studied
-partly with AG's help - by my colleague Paul Anderson, a semi-retired
professor of zoology at the University of Calgary in Canada. One of
Paul's most important discoveries is that males in WA's Shark Bay appear
to defend territories during the breeding season. .They display in their
territories, both to warn off rivals and to attract mates.
Scientifically this is known as lek behaviour.
Paul has also found that seagrasses are not the only food sought by
dugongs. In Shark Bay he has seen them digging for mussels and sea-pens,
the feather-like relatives of corals. In Moreton Bay, sea-squirts have
been found in dugong droppings. From the gut contents of dugongs caught
in Townsville shark nets, we know they also eat algae and sea-cucumbers,
although it's not yet known whether this is deliberate.
(See Pictures Here)
|
- Stonefish and stingrays sometimes give dugongs
nasty, even lethal, surprises as they feed. Crocodiles, killer whales
and sharks are among their few natural predators, but are not always the
victors. I have occasionally seen dugongs with scars that show they have
recovered from shocking shark bites.
TO gauge the impact of natural disasters, hunting and the fishing-net
toll on Australian and Torres Strait dugongs, it was clear that I would
have to determine their numbers accurately. The Great Barrier Reef
Marine Park Authority was particularly concerned because the large
number of dugongs in the region was one of the reasons behind its World
Heritage listing. Because they are very
difficult to see from boats, the only feasible method of counting
dugongs is by aerial survey. I began dugong censuses in 1984. The
results have been surprising. My aerial surveys of the waters of the
Great Barrier Reef Marine Park and Torres Strait, and others by Bill
Freeland and his colleague Peter Bayliss, show that
Since June 1988, Tony has been studying dugongs in Moreton Bay,
where more than 500 graze within 25 km of Brisbane's waterfront suburbs.
The bay's dugongs were believed to have been wiped out by a cottage
industry that exploited their oil from the mid-1800s to around the
1940s. Dugong oil was thought to cure everything from tuberculosis to
joint pains. For decades marine biologists working in the area had never
seen a dugong there. Then, during an aerial survey in May 1976, George
Hein-sohn could not believe his eyes when he spotted a herd of some 200.
Dugong mothers are very attentive, communicating with their young
through bird-like chirps and high-pitched squeaks and squeals. The calf
never ventures far from its mother and frequently rides on her back.
Mothers appear highly protective. A report from Torres Strait told of
one sacrificing her life to save her calf from a shark, luring the
predator into increasingly shallow water until both she and it became
grounded. This did not stop the shark from
fatally mauling her, but the calf fled to safety. (See
Pictures Here)
|
- Crocodiles, killer whales and sharks are among
their few natural predators, but are not always the victors. I have
occasionally seen dugongs with scars that show they have recovered from
shocking shark bites.
TO gauge the impact of natural disasters, hunting and the fishing-net
toll on Australian and Torres Strait dugongs, it was clear that I would
have to determine their numbers accurately. The Great Barrier Reef
Marine Park Authority was particularly concerned because the large
number of dugongs in the region was one of the reasons behind its World
Heritage listing. Because they are very
difficult to see from boats, the only feasible method of counting
dugongs is by aerial survey. I began dugong censuses in 1984. The
results have been surprising. My aerial surveys of the waters of the
Great Barrier Reef Marine Park and Torres Strait, and others by Bill
Freeland and his colleague Peter Bayliss, show that (See
Pictures Here)
|
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