Research
Tagging
White sharks: Four tagged white sharks (Rolf, Bomber,
Michael, SamC)
[Home] [Tagging
procedure]
[Tracks: Rolf | Bomber | Michael | Sam
C | Combined]
How the four white sharks were tagged
Finding sharks
Rolf, Bomber, Michael and Sam C
were tagged during November 10-13 at The Neptunes, one of the most reliable
and accessible places for finding white sharks in southern Australia.
The Neptunes is a group of islands some 60 kilometres south of Port
Lincoln in South Australia. They rise from Australia's continental shelf
in a region where water depths range from 40-100 m.
"The sharks are here primarily to feed on seals from the fur seal
colony at North Neptune Island," CSIRO research scientist Barry Bruce
says.
"Our analyses of logbook records kept by tour operators for
the past 5-6 years have shown that on average, the winter–spring
period is the best time to find sharks in the area.
"But we don't yet know the reason for this pattern, which does
not appear to relate to the behaviour of the seals."
Mr Bruce says the Neptunes is a well-established site for tourism and
research purposes.
"Tour operators view sharks there on a regular basis and we have
worked with them and tagged extensively in the area. We have a good idea
of how sharks behave in this environment and the necessary research permits
are in place,' he says.
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Attracting the sharks
"More than 250 white sharks have been tagged in Australian waters
as part of CSIRO's tagging program. Most have been tagged with conventional
tags and many of these sharks are resighted at the Neptunes."
The vessel used for the tagging was the Calypso
Star, a 57-foot charter
boat owned and skippered by Rolf Czabayski and crewed by Andrew Wright.
Also onboard were Barry Bruce and Russell Bradford of CSIRO Marine and Atmospheric Research,
John Beaumont from the SA Police, who has assisted in several white shark
research trips, Megan Storrie, a shark researcher from NSW and underwater
cinematographer David Riggs.
Each day, the Calypso Star was anchored in North Neptune Bay in waters
of 10-20 m and a berley mix of fish products - mainly tuna mince and tuna
oil - was dripped into the water.
The wind and currents would create a berley trail leading away from
the boat, and the team would wait for a shark to follow the trail to the
vessel.
"The evidence suggests that such berley trails may attract sharks
from distances up to only a few kilometres," Mr Bruce says.
"So really we're attracting sharks that are already in the area
because of the natural attraction of the seal colony. We can go for days
or sometimes weeks without seeing a shark. We don't always see sharks
every each day."
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Catching a shark
Most white sharks can be tagged without capturing them. Conventional,
acoustic and pop-off archival tags are attached using a long pole as the
shark swims by the boat.
But because the satellite tracking tags must break the surface to transmit,
they must be attached with greater precision to the top of the dorsal
fin. The only way to do this is to catch and restrain the shark while
the tag is attached to the fin.
The sharks are caught using a 12 mm rope and a short, heavy wire trace
which is quite thick so it won't cut the shark's jaw.
Because the sharks are bold, they can be hooked in a carefully controlled
way, quite near to the boat. This is done using a galvanised hook with
the barb partially removed so that if it can't be taken out, it can be
cut and will fall out on its own.
"We wait for the shark to present itself near the boat, and feed
it a hook baited with tuna which is suspended under a small float,"
Mr Bruce says.
"The shark must take the hook on the left hand side in close to
the corner of the jaw so that it can be manoeuvred efficiently and safely
in and out of the cradle at the back of the boat.
"It is brought into the cradle at the rear of the boat from left
to right. It comes in one side, lies in the cradle while tagged, then
swims out the other side. The left side is presented to us, making the
hook easier to remove or cut.
"We pull the bait away if the shark is in the wrong position. It's
all about being able to control and work on the shark, and minimising
risk and injury to the shark and to us."
Usually the shark will make an initial run with the bait. Extra floats
are clipped to the rope as it goes. The idea of the capture process is
to let the shark tire itself gradually, not for it to be a fight.
"We have to be very patient to minimise risk to the shark,"
Mr Bruce says.
"The purpose is to get the shark to a stage where it is tired enough
so that it can easily be led into the cradle and will be quite calm.
"They must not be tired too much or they may not swim away successfully.
This process can take 20-90 minutes, depending on the shark, although
not necessarily on its size."
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Attaching the tag
Once tired, the shark is led into a cradle at the back of the boat.
The four-metre long cradle, purpose-designed and built by Melbourne
Aquarium, is attached to a crane and duckboard at the back of the boat.
It consists of two aluminium poles slung with flexible, heavy-duty rubberised
material.
Once the shark is on the cradle, the crane pulls the outer pole towards
the boat to contain the shark. This technique was first trialled in March
2004 when the white sharks Bruce and Lulu were tagged,
also at North Neptune Island.
The shark remains in the water all the time once in the cradle. A hose
is used to pump seawater and oxygen into the shark's mouth. This replicates
the effect of swimming, which the sharks must do continually in order
to pass enough water over their gills to breathe.
The oxygen may also provide a slight sedative effect and the process
of administering it was developed by staff at Melbourne Aquarium.
Two teams of two people work to remove the hook and attach the tag.
The tag is carefully pinned near the top of the dorsal fin. The pins are
designed to disintegrate over time so the tag eventually will fall off
after the batteries are exhausted. The hook is either removed, or cut
as close to the shark as possible and left to fall out by itself.
A tissue sample is taken from the shark for genetic analysis. This is
part of a genetic study that is investigating how many different white
shark populations exist worldwide and how they are linked.
When the tagging process (which takes 4-6 minutes) is finished, the
cradle is loosened and the shark swims free.
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How the tag works
The satellite tags are fitted with a saltwater switch, which turns them
off when underwater to save battery power. When at the surface, the tags
transmit a unique code detected by a series of satellites fitted with
ARGOS receivers.
The satellites relay the shark's position to a ground station in France
and CSIRO scientists use the positions to plot each shark's track.
"We hope to get up to six months out of the tags but it depends
on how frequently they transmit, or how much the shark comes to the surface,"
Mr Bruce says.
"White sharks regularly swim up and down from the surface to the
bottom. We think they may be picking up cues to help them navigate and
locate areas where they can find food. They tend to spend more time at
the surface when they are in 'travelling' mode."
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Choosing the shark's names
All white sharks received names when they are tagged. In this case,
the sharks are named after either people who were onboard or their relatives.
Rolf is named after the owner and skipper
of the Calypso Star, Rolf Czabayski.
Bomber is named after John Beaumont who has
been part of several shark tagging trips.
Michael is named after Barry Bruce's son.
Sam C is named after one of Rolf Czabayski's
grandsons.
Tag log
November 10: tagged and released 'Rolf', 3.8 metre adult male, estimated
weight 500 kg, estimated age 9-10 years
November 11: tagged and released 'Bomber', 3.2 metre sub-adult male,
estimated weight 325 kg, estimated age 7-8 years
12 November: tagged and released 'Michael', 3.2 metre sub-adult male,
estimated weight 325 kg, estimated age 7-8 years
November 13: tagged and released 'Sam C', 3.2 m sub-adult male, estimated
weight 325 kg, estimated age 7-8 years
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