The IUCN/SSC Shark Specialist Group
Shark News 7: June 1996
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Archival tagging of sharks in
Australia
John Stevens, CSIRO Marine Laboratory, Tasmania, Australia
Archival tags developed by CSIRO and Zelcon Technic Ltd have been
used successfully on southern bluefin tuna to provide continuous
records of long-distance fish movements, diving and feeding behaviour.
These mini computers weigh 25 g, have 1 megabyte of flash RAM and
contain an accurate time clock and depth, temperature and light
sensors. Diel changes in light are used to calculate longitude and day
length is used to calculate latitude. The tags can log data at
predetermined intervals for nine years and store it for 20 years.
Whale shark. Photo: Jeremy Stafford-Deitsch.
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We have recently received funds to use this technology on both
school Galeorhinus galeus and whale sharks Rhyncodon typus.
School sharks are a target species in the $15 million/year Southern
Shark Fishery. CSIRO and The Victorian Fisheries Agency (VFRI) play
a major role in the assessment of school shark stocks and in researching
the biology and population dynamics of this species. School sharks
spend much of their time on the continental shelf where they are
fished by demersal gillnets and longlines. However, they also occur
on the upper slope and at times extend into the oceanic pelagic zone,
with conventional tagging showing a number of trans-Tasman
migrations to New Zealand. Archival tagging will be used to provide
information on their swimming depth and longer-distance movements.
A question of particular interests to scientists and industry is whether
pupping grounds for the whole stock are restricted to Victoria and
Tasmania. Archival tagging of pregnant females may provide the
answer. We (CSIRO and VFRI) have trialled different attachment
methods and tag designs using 'dummy' tags. Internal tags (as used on
the tuna) are surgically implanted in the body cavity; the light sensor
being mounted on an external streamer. Two external fin-mounted
designs have been used; the rectangular shape of the standard tag and
a torpedo-shaped hydrodynamic version with low drag. Perhaps
surprisingly, most returns have been of the internal dummy design.
Snorkelling with whale sharks is an important ecotourist industry
at Ningaloo Reef in northern Western Australia. Aggregations of
whale sharks appear each year in March and April close to the
coast, probably in response to increased productivity associated with
mass coral spawning. We have received a grant under the National
Ecotourism Program to use standard telemetry, archival tags and
satellite tags to study the short and long term movements of whale
sharks at Ningaloo. Three years ago we successfully tracked two
sharks (one for 26 h) and obtained interesting data on their swimming
depth and diving behaviour. We also attached six archival tags and,
although we retrieved one from a shark after 24 hours, none have been
seen subsequently, However, at
least some individuals are known
to return each year (recognised
from distinctive wounds or
markings) so by choosing some of
these sharks we are hopeful of
success with further tagging.
Whale sharks have been
successfully tracked for several
months using satellite tags by a
group in California and we will
also try similar tags at Ningaloo.
While archival tags can be used
to obtain positional data
underwater (providing the fish
does not go below 100-150 m,
the depth of usable light levels)
satellite tags must be at the surface
for transmission.
John Stevens, CSIRO Marine
Laboratory, GPO Box 1538,
Hobart, Tasmania 7001, Australia.
Email: john.stevens@ml.csiro.au
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