[ASC-media] Sonar reveals the secret fears of fish

joanne.finlay at dpi.nsw.gov.au joanne.finlay at dpi.nsw.gov.au
Tue Dec 19 23:05:18 CET 2006


NSW Department of Primary Industries
MEDIA RELEASE
20 December 2006

SONAR REVEALS THE SECRET FEARS OF FISH

The first Australian trials of a specialist underwater acoustic camera 
have shown it can be used to overcome a major difficulty in fisheries 
research.

Observation of fishes' natural behaviour in murky water is now possible, 
thanks to the dual frequency identification sonar camera, known as a 
DIDSON.

NSW Department of Primary Industries fisheries scientists say high 
resolution sonar images from the camera will be invaluable for developing 
management strategies to protect the long-term survival of fish species.

Scientists recently assessed the DIDSON at the mouth of the Murray River 
where, in 1940, a series of barrages were built across the river at 
Goolwa.

To restore fish passage up the River, two fish ladders were constructed 
across the barrages in 2004 by the Murray Darling Basin Commission. 

Fisheries researcher Lee Baumgartner said a survey by a research team from 
NSW, Victoria and South Australia showed the ladders were being used by 19 
fish species, but not black bream and mulloway, both iconic species for 
the region.

DPI trials with the DIDSON showed that black bream "really freak out" when 
they encountered the fishways, according to Mr Baumgartner.

"They swim up to the ladder, get spooked and then swim away quickly," he 
said.

The camera uses sound waves to pick up acoustic echoes of fish swimming 
and then converts them into digital images, which can be viewed on a 
personal computer.

Mr Baumgartner said the sonar images show that yellowbelly, bony bream and 
even small fish like smelt and gudgeon all swim through the fishways. 
However the black bream won't. 

"We are now using the DIDSON to find out if there is something about the 
fishway that they do not like. Could it be that the mouth of the ladders 
is too small for them? Or could the problem be the rapid transition from 
salt to fresh water? The DIDSON will be invaluable tool in answering these 
questions."

DPI recently purchased a DIDSON at a cost of $140,000, after assessing its 
potential for fisheries research. 

Because it is able to observe fish at night and in dirty or turbid water, 
the DIDSON opens the door for new research directions and ideas for 
helping migratory fish.

The camera eliminates the need for scientists to physically catch fish to 
gather information about their biology and ecology, and allows scientists 
to work with fish non-destructively, without traditional gear like nets or 
traps.

By directly observing how fish behave when they migrate, feed and spawn, 
researchers will be better placed to develop management plans to ensure 
the fishes' long-term survival.

The technology was first developed in the 1990s by the US Navy to enable 
divers to detect mines attached to the hull of ships.

Contact: Lee Baumgartner, Narrandera, on (02) 6959 9027 or 
lee.baumgartner at dpi.nsw.gov.au.
Media inquiries: Joanne Finlay on (02) 6391 3171, 0428 491 813 or 
joanne.finlay at dpi.nsw.gov.au
 
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