July 14, 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 62 miles 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 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 dove when seawater was used, while more than 50 took dives during the vegetable oil trial.
