(Narrator) It's not surprising that for most Australians
the idea of grappling with a live shark has very little appeal
but for researcher Stephanie Davenport it's all in a day's work.
Her efforts may help expand the opportunities
for us to sink our teeth into a piece of shark.
For many Australians, especially in Victoria,
this is already a regular event. Slices of shark known as flake
are a popular and renowned seafood.
Flake comes predominantly from two species,
school shark and gummy shark
taken from the cold waters of Southern Australia.
But in the warm waters off northern Australia there is another major
shark fishery. Its produce is destined for the markets of Taiwan.
Since the early 1970s Taiwanese trawler operators have been paying
about a million dollars each year for licence and access fees.
In the mid ‘70s their yearly catch was about 10,000 tonnes.
It was not until the 200 kilometre Australian fishing zone was declared
in November 1979 that the fishery came under Australian control.
Until then nothing was known about this fishery except that
large numbers of sharks were being taken.
This caused concern since sharks are particularly
susceptible to overexploitation.
There are several reasons for this.
Sharks generally have a long gestation period
since many species give birth to live young.
They often have a slow growth rate and a late attainment of sexual maturity.
There is also a much closer relationship between
the number of young produced and the size of the parental
population than in other fish.
There are many species of sharks in the warm northern Australian waters
including the large tiger sharks and hammerheads.
Commercial and scientific interest however
has focused on the smaller blacktip species.
Food researchers at Royal Melbourne Institute of Technology
have carried out a series of taste panel samplings
to see whether the northern species
were acceptable to the southern palate.
Frozen sharks were sent to Melbourne
and served up with similarly prepared flake
and although the two varieties differ slightly in texture and taste
the panels found the blacktip shark to be quite palatable.
So there was obviously a potential market for the northern sharks
but there were many scientific questions to be answered
before a properly managed commercial
fishery could be established in Australia.
A collaborative research program was set up between
CSIRO's Division of Fisheries,
the Department of Primary Industry
and the fisheries agencies of the Northern Territory,
Queensland and Western Australia.
Early research into the blacktip species
concentrated on their biology and population structure.
Sharks can be difficult to age
but it is possible by counting growth rings on vertebrae.
In order to get more detailed information
it was necessary to study the sharks in their own habitat
so in 1984 the 21 metre gillnet vessel Rachel was chartered
to make a series of 12 cruises
covering waters between Broome and Cairns.
Dr John Stevens was project leader.
(Dr John Stevens) Well there were two stages to this research program.
The first was to obtain basic biological information on these blacktip sharks
and the second stage was where we carried out a large
scale tagging program in conjunction with exploratory
fishing to determine the catch rates.
The purpose of the tagging was to determine the number
of stocks of blacktip sharks in northern Australian waters
and to describe their geographical range
and from the tagging we can estimate some of the population
parameters, that is, the rate at which sharks are
born, the rate at which the populations grow and
look at the death rate and ultimately to make
estimates of the population size
and this information will then be used by the
Department of Primary Industry
to more effectively manage the fishery.
(Narrator) On this survey the Rachel passed inside the Barrier Reef
north of Cairns, then through the Torres Strait
and across the Gulf of Carpentaria.
(Stephanie Davenport) Well we'll try 500 metres to start
to see what's in the water and take it from there.
If we do well on that we'll just keep fishing the 500 metres.
Otherwise we could use the four kilometre net.
(Female) Yeah.
(Narrator) During the day sharks are caught mainly by handlining.
A trail of chopped fish draws the sharks to the boat
and barbless hooks are used to minimise injury.
The sharks are carefully measured, tags clipped
onto the dorsal fin and then they are released.
The success of the program depends on the cooperation of
Taiwanese and Australian fishermen in returning the tagged sharks.
For this they are offered a reward in addition to the market value.
The blacktip sharks are also caught using a longline
released from a reel at the stern.
Baited hooks are hung at regular intervals from the
longline which is suspended by buoys.
During the night gillnets are laid.
Polystyrene floats are clipped to the top of the net
so that it hangs like a curtain below the surface.
About a thousand sharks are tagged on each of the cruises.
Some sharks are injected with tetracycline dye before being released.
The dye is absorbed by the vertebrae
forming a visible reference point when the shark is recaptured.
An important question is whether sharks in one
area come from common or different genetic stock.
Using a technique called electrophoresis
scientists can analyse muscle tissue.
Different enzymes are separated from the tissue
thus showing the amount of genetic variation.
This will indicate whether the sharks all come from one breeding stock
or whether they form different breeding populations.
So after all this research
are we any closer to seeing blacktip sharks on Australian dinner tables?
(Dr John Stevens) Well we've come a long way from the days before
this research program when virtually nothing was known about the fishery.
Now we've got good basic information on the biology of the two main
species in terms of reproductive cycles, age and growth
and diet and population structure.
From the results of the tagging program
where we've tagged sharks right around northern Australia
from Broome in the west to Cairns in the east
and we've tagged over 10,000 sharks and had about 250 recaptures to date,
sharks have moved distances up to 1,100 kilometres
and over about 16% of the population
have moved distances over 100 kilometres.
(Narrator) The large distances travelled by the sharks
has been something of a surprise. The researchers found for instance that
some sharks have moved from the inshore waters
where the Australian fishery operates out into the Taiwanese zone.
Information like this will have important implications
for any management strategy, however,
it will be a number of years before the researchers can
say anything definitive about the state of the stocks.
At the moment they're still waiting for more tags to be returned.