[ASC-media] Unlucky reef shark leads researchers to better understanding

Wendy Ellery w.ellery at aims.gov.au
Thu Apr 17 00:40:58 CEST 2008


17 April 2008

Unlucky reef shark leads researchers to better understanding

The fate of an unfortunate reef shark, caught and eaten 80 km from where
it was tagged in a Sanctuary Zone in the Ningaloo Reef Marine Park off
the Western Australian coast, is helping to unravel the mysterious life
and movements of sharks.

An AIMS project to tag the common grey, black tip and white tip reef
sharks and monitor their movements through the Marine Park is in its
early stages and has already turned up useful information about shark
movements, thanks to the shark that became a fisherman's dinner.

The black tip shark, a mature female about 1.4 m long, was caught by a
fisherman who was standing on rocks at Gnaraloo, well south of the
Sanctuary Zone.  The recreational fisherman contacted AIMS when he saw
the details on the attached tag.  Gnaraloo is a popular fishing spot
north of Carnarvon and the man was fishing legally.

"We are delighted that the fisherman made contact with us," AIMS fish
biologist Dr Mark Meekan said.  "He did exactly the right thing, and as
a result we now know more than we did about how far from the protected
area these animals can travel."

The shark was tagged and fitted with an acoustic transmitter last
November by Charles Darwin University PhD student Mr Conrad Speed, who
is tagging reef sharks as part of his studies, under Dr Meekan's
supervision.  The shark had been heavily pregnant at the time of tagging
and it is likely to have given birth soon after.

It was last detected by an acoustic monitor on 5 January, still in the
Sanctuary Zone, but on 3 February 2008 it was caught and eaten south of
Ningaloo.  Some time in that month, it travelled far away from the safe
area.

Mr Speed tagged 10 sharks in Coral Bay last November, including the one
that was caught. 

Scientists have long surmised that reef sharks travel long distances,
well outside those areas set aside for the protection of marine life.
Little is known, however, about the impact of fishing and if this is
great enough to put species at risk.

"The Sanctuary Zones, which cover about 30 per cent of the Ningaloo Reef
Marine Park, are meant to protect sharks and other marine creatures, but
it is difficult when very little is known about the migration patterns
of top order predators and their prey," he said.

Dr Meekan hoped that other fisherman would make contact with AIMS if
they caught a tagged shark.  A distinctive bright yellow tag is clearly
visible on the dorsal fin of those sharks in the study. 

Reef sharks have a variety of behaviours that are currently mysterious,
not just their propensity to cover long distances in unknown travel
patterns.  For example, large numbers of adults and juveniles congregate
in knee-deep water at Coral Bay in the Ningaloo Marine Park, becoming
something of a tourist attraction with visitors wading into the water
with them.

Scientists speculate that pregnant females may be using the warm,
shallow water as a kind of incubator to speed up the development of
their embryonic young, while juveniles may gather there as protection
from predators.  The AIMS shark tagging and monitoring project is
designed to better understand these creatures.  Using permanent
installations of acoustic "curtains", lines of reef-based receivers
spanning the reef that pick up the "ping" from the transmitter attached
to tagged sharks as they cross the receivers' field of detection, plus
arrays of receivers closer to shore, scientists are hoping to learn much
more about the movement of sharks around Ningaloo.

When a tagged creature swims across the detection field, the date and
time are recorded electronically.  At present, the data from the
curtains and arrays is being downloaded every six months for analysis.
This technology is moving ahead quickly and Dr Meekan hopes in a few
years that real-time monitoring may be possible, enabling instant access
to data.

At present, AIMS is monitoring the movements of around 20 Ningaloo reef
sharks.  Mr Speed's next tagging expedition is scheduled for October
this year and it is hoped that a total of 100 sharks will be tagged and
monitored in this project.

For further information, please contact:


Dr Mark Meekan, fish biologist
Scientist in charge, AIMS Darwin
Ph:  08-8920 9240; 0429 101 812
E-mail:  m.meekan at aims.gov.au

Ms Wendy Ellery
AIMS Media Liaison, Townsville
Ph: 07 4753 4409; 0418 729 265
E-mail:  w.ellery at aims.gov.au


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