(Fwd) Net closing on coral reef bombers

GJ Gast gjgast at ams.greenpeace.org
Fri Jan 17 05:12:00 EST 2003

FYI. Text continued below links. Cheers, GJ.

Net closing on coral reef bombers

09:30 13 January 03

Exclusive from New Scientist Print Edition

Coastguards will soon be hot on the trail of fishermen who are
illegally blasting many coral reefs to rubble as they use bombs to
increase their catch.

    Up come the fish, as more coral turns to rubble (Image: HKUST)
  <http://www.newscientist.com/img/shim.gif>    Up come the fish, as
coral turns to rubble (Image: HKUST)
Blast fishing is a problem in many places throughout South-East Asia
and along Africa's east coast. Although it is illegal, efforts to
it are hampered by poor detection rates.

"Blast fishing is often known to occur in a region through sporadic
arrests and anecdotal observations, yet the scale of the problem is
often not appreciated as most blasts go undetected," says George
Woodman, who works on the listening project led by the marine sensors

group at the Hong Kong University of Science and Technology.

One problem that has hampered development of a detection system for
underwater explosions is the cacophony produced by the claw-clicking
"pistol" shrimp that live on reefs. Pistol shrimp near the detection
system can generate short-range shock waves that are bigger than the
signal from a distant bomb. But now the Hong Kong team has solved the


The researchers use underwater microphones, or hydrophones, to pick
the noise from blasts. The detection range for each hydrophone is
around 30 kilometres and the team has developed software to calculate

the direction of a blast from the slight time difference between the
noise reaching each of three hydrophones. Two such sets of
could be used to triangulate the position of an explosion to within
metres over a 10-kilometre range.

Fertiliser and fuel

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Hong Kong University of Science and Technology

Coral reefs in Sabah

Reef  <http://www.reefimages.com/Shrimp/Shrimp22.htm> shrimp


Woodman and his team first had to make sure they could reliably
recognise the sound generated by home-made bombs in the shallow
where reef-smashing fishermen operate. They set off controlled
explosions using bombs made from a mix of fertiliser and fuel oil -
using sandy areas of the seabed to minimise ecological impact.

Their system distinguishes the noise of an underwater explosion from
that of the shrimps' clicking by recognising differences in the
of the sound produced. An explosion contains more energy overall and
lasts longer than the clicks. In contrast, the noise from an outboard

motor is more prolonged, but its peak signal is smaller. Their system

will be described in a future issue of Marine Pollution Bulletin.

The team has already tested one of their hydrophones in a survey for
the Sabah Parks Authority in Tunku Abdul Rahman National Park, off
Kota Kinabalu in Sabah, Malaysia.

"Over a 10-day stretch we picked up 15 blasts using one listening
station [hydrophone] and we are very confident we can determine the
direction of the blasts to within about 0.2 degrees," says Woodman.
They now hope to mount a trial with three hydrophones.

Michelle Knott

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Dr Gert Jan Gast
Seas and Oceans Campaigner, Greenpeace Netherlands
Keizersgracht 174, 1016DW Amsterdam, The Netherlands
Phone +31 20 5236655
Mobile +31 6 5206 2976
Fax +31 20 6221272

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