To Tag a Shark (1986)
Shark, commonly known as flake, is a widely accepted seafood. It comes from several species of cold water shark.
But in the tropical waters north of Australia, there”s another shark fishing industry. Here, Taiwanese and Australian fishermen have been catching the Blacktip shark.
In order to establish sound management practices for developing this industry, CSIRO researchers from the Division of Fisheries have undertaken a series of cruises in Northern Australia to study the biology and reproductive behaviour of the Blacktip species.
Some one thousand sharks are caught and tagged on each cruise and much depends on the co-operation of Taiwanese and Australian fishermen in reporting the capture of tagged sharks.
Meanwhile food tasting experiments are looking at the acceptability of northern sharks to southern palates.
[Image changes to show a shark swimming beside a boat as Stephanie pulls it in on a handline. Text appears: To Tag a Shark] 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.
[Image changes to show Stephanie lifting the shark onto the boat’s deck]
Her efforts may help expand the opportunities for us to sink our teeth into a piece of shark.
[Image changes to show a shopkeeper in a takeaway shop wrapping up fish and chips in butchers paper]
For many Australians, especially in Victoria, this is already a regular event. Slices of shark known as flake are a popular and renowned seafood.
[Image changes to show the outside of the takeaway shop named Pelican and advertising they sell fresh flake]
Flake comes predominantly from two species, school shark and gummy shark taken from the cold waters of Southern Australia.
[Image has change back to sharks swimming near the surface of the water and then Stephanie on the boat taking still photos]
But in the warm waters off northern Australia there is another major shark fishery.
[Image changes to show Taiwanese fishing boats full of caught sharks]
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.
[Image changes to show a map of Australia and the fishing zone shaded in around it]
It was not until the 200 kilometre Australian fishing zone was declared in November 1979 that the fishery came under Australian control.
[Image has changed back to Taiwanese fishing boats laying out nets into the ocean and the on-deck preparation of the fish including cutting off their fins]
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.
[Image has changed back to show a shark swimming near the ocean surface]
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.
[Image changes to show a hammerhead shark caught using a handline, being pulled onto the boat]
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.
[Image changes to show a researcher giving a plate of food to a lady to sample]
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.
[Image changes to show several people on the taste panel sampling the fish and writing down their findings]
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.
[Image changes to show a man and woman seated at a restaurant table eating fish and chips]
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.
[Image changes to an aerial shot of the CSIRO buildings in Hobart]
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.
[Image changes to show Stephanie examining something under a microscope while Dr Stevens records the information]
Stephanie Davenport: It’s six.
Dr John Stevens: Two point six.
Stephanie Davenport: Three point five.
Narrator: Early research into the blacktip species concentrated on their biology and population structure.
Stephanie Davenport: Four point four. Five point two. Six point three.
Narrator: 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.
[Image changes to show the Rachel vessel and fishing nets being prepared and then to Dr John Stevens, CSIRO Division of Fisheries Research]
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.
[Image changes to sharks being caught and tagged]
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.
[Image changes to show the shark being released back into the ocean]
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.
[Image changes to show Stephanie looking over maps and discussing with the boat’s captain]
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.
[Image changes to show Stephanie catching a shark with a handline and pulling the shark onto the boat for measuring and tagging]
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.
[Image changes to show a poster that informs fishermen that rewards are offered for returning tagged sharks, written in both English and Taiwanese]
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.
[Image changes to show Stephanie and crew preparing the line and casting it into the ocean]
Baited hooks are hung at regular intervals from the longline which is suspended by buoys. During the night gillnets are laid.
[Image changes to show the nets being prepared and cast into the ocean]
Polystyrene floats are clipped to the top of the net so that it hangs like a curtain below the surface.
[Image changes to show a shark being freed from the net and then measured and tagged]
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.
[Image changes back to Stephanie examining a shark vertebra under a microscope and Dr Stevens recording the information]
Narrator: 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.
[Image changes to show a scientist analysing shark 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?
[Image has changed back to Dr Stevens]
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.
[Image changes back to the fishing boat on the ocean]
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.
[Credits: With thanks to the Master and Crew of the Rachel. © 1986 CSIRO Australia]