The IUCN/SSC Shark Specialist Group
Shark News 3: March 1995
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Whale sharks in Western Australia
John Stevens, CSIRO Australia
Over the last few years a significant ecotourist industry based on
snorkelling with whale sharks has developed at Ningaloo reef in north
Western Australia. Each year during March and April, aggregations of
these sharks appear close to the reef which is only a kilometre or so
offshore. During the whale shark season the normally quiet town at
Exmouth comes alive with international tourists and television crews
wanting to swim with and film the whale sharks. Spotter planes are
used to locate the sharks and direct the dive-boats into contact.
Management regulations control the number of vessels in the area
and in contact with a particular shark, the number of snorkellers in the
water and contact time and minimum approach distances in an
attempt to minimise disturbance to the animals. Other than that the
whale sharks presence in the area is most probably in response to
increased productivity in the food chain associated with the mass
spawning of corals, little is known of their local population structure,
behaviour and movement patterns.
Whale shark. Photo © Jeremy Stafford-Deitsch.
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Last March myself and John Gunn, also from CSIRO, spent ten
days at Ningaloo doing some tracking and tagging work to try and find
out more about the whale sharks movement patterns. We looked at
short term movements using standard acoustic telemetry techniques
and long term movements using recently developed archival tags
('smart' tags or data loggers). John Gunn is heading up a CSIRO
project which has developed and pioneered the use of these tags on
southern bluefin tuna. The tags were designed by CSIRO in conjunction
with a local electronics company and they measure and store
information on the date, time, swimming depth, light levels and
temperature of the surrounding water. Data are collected at
predetermined intervals and logged for 8-9 years and can be stored
for up to 20 years. On retrieval of the tag the data are downloaded and
the light intensity data used to calculate geographical locations of the
fish providing a record of where it has been overthat period accurate
to about one degree of latitude and longitude. The tags measure 90
x 24 x 18 mm, weigh 60 g in air and have 256 kilobytes of RAM
memory, enough space for some 60,000 sets of data on depth,
water temperature, light levels and time. The tags are expensive
and consequently only cost effective where high recapture rates can
be expected. In the case of whale sharks at Ningaloo it is known from
individuals with distinctive markings and fin damage that many of the
same sharks return each year.
Both the acoustic transmitters and the archival tags were attached
to the sharks' first dorsal fin using a small detachable stainless steel
head mounted on a spear which was propelled using a Hawaiian
sling. Tagging was carried out underwater by a snorkeller with the
shark usually showing little or no reaction to being tagged. During
our visit we saw some 35 whale sharks. Two individuals were tracked,
one for a period of 26 hours, providing interesting data on horizontal
movements along the reef, diving behaviour, the time spent at
different positions in the water column during the day and night, and
on swimming speed. Six archival tags were attached (one was
retrieved after 24 hours providing further data on swimming depth
and diving behaviour) and we are hopeful of getting at least one back
this year which would provide fascinating information on where the
sharks have been after leaving Ningaloo.
This year we hope to go back and do some more tracking work,
deploy more archival tags and also try some satellite tracking.
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