Strange, I always though shark liver was the best seabird attractant ...
http://www.abc.net.au/science/news/stories/s1688117.htm
Shark oil saves seabirds
Jennifer Viegas
Discovery News
Monday, 17 July 2006
An old fishermen's remedy for preventing seabirds from becoming bycatch
turns out to be true, according to a new study on the effectiveness of
shark liver oil at warding off birds.
Using the stinky oil might help save seabirds, which often have fatal
interactions with longline fisheries.
These fisheries use a line up to 100 kilometres long, often with
additional branching lines.
Each line is rigged with hundreds or even thousands of barbed, baited
hooks.
Seabirds, including some endangered species, often dive for the bait
and fish. The birds can become entangled in the lines or injured,
sometimes fatally, by the hooks.
Alex Aitken, a New Zealand fisherman for over two decades, uses the
traditional shark liver oil as a deterrent.
Sharks themselves are bycatch in the snapper longline fishing industry,
but government and industry regulations monitor their numbers in New
Zealand.
Aitken drips the oil into water around fishing boats to deter the
birds. In 2003, he entered his concoction in the SEO/BirdLife
International competition for bycatch reduction. He won.
To test the oil, scientists Johanna Pierre of New Zealand's Department
of Conservation and Wendy Norden of wildlife conservation group Audubon
California conducted experiments off New Zealand's North Island. The
seabird community there includes the endangered black petrel.
The researchers dripped the shark liver oil from a plastic container at
the stern of their vessel, while they set out 200 baited hooks on lines.
As controls, they later conducted the same test using vegetable oil and
seawater.
The shark liver oil did not affect fish catches, but it did
dramatically reduce the number of times seabirds dived for the hooks.
For example, after nine minutes, only two or so birds went for the
hooks when shark oil was present. Around 40 birds dived when seawater
was used, while more than 50 took dives during the vegetable oil trial.
Pierre and Norden think the birds might even have been attracted to the
vegetable oil, but the shark liver oil was a successful repellent.
Their findings are published in the July issue of the journal
Biological Conservation.
"We are not sure what happens when the seabirds smell the oil," Pierre
says.
"However, when the oil is released at the stern of the vessel, the
effect ... is next to immediate. The birds disperse away from the
vessel, sufficiently far that they can't be seen. One or two birds may
come in from time to time and do wide looping flights around the
vessel, but they typically don't land or stick around for long."
The repellent seems to have more to do with the noxious smell of the
oil, or its consistency in the water, rather than the birds' fear of
sharks.
"I think it's unlikely that they have a negative reaction to the smell
of sharks per se. This is because the birds have no hesitation to
eating shark livers when they are whole and they can also eat shark
waste readily," Pierre explains.
The deterrent only appears to work as long as the dripping is
continuous. Once the oil flow stops, Pierre says the birds "somehow cue
into the fact that the vessel area is now attractive/interesting, not
oily/nasty".
Though shark liver oil is a natural product, it may be problematic to
introduce large amounts into marine environments.
Pierre and Norden hope the effective ingredients in the oil may be
identified and isolated. It could be that these ingredients may be
found in products other than shark liver oil, but this has yet to be
determined.
In the meantime, the scientists suggest caution in using large amounts
of the oil, and hope alternatives such as aerosol mists of the
effective ingredients can be developed in the long run.
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