Porpoise-speak Prevents Net Death
Together with L-3 ELAC Nautik, a manufacturer of hydro-acoustic systems in Kiel, Boris Culik developed a click generator and programmed it in such a way, that it produces corresponding warning clicks with increasing frequency. First tests have shown that the animals understand the signal correctly and react with intensive acoustic inspection.
The goal of this research project, supported by the circle of friends for preservation of vagrant wild life (UNEP/CMS), is to create recognisable warning sounds for the porpoises. Hannes Jaenicke, president of the circle of friends, declared: "Eighty percent of the porpoises die in gillnets. The warning signal is an important immediate measure to decrease the by catch in the North Sea and the Baltic Sea.
Porpoises communicate mainly by clicks. Certain click sequences, so-called click trains, are understood as warning. The reaction of porpoises to the clicks has been tested by Boris Culik and the student Simon Winkler during tests at the Fjord & Baelt Center in Kerteminde, Denmark. When examining the noise source closely, the four test animals increased the number of their clicks by forty percent. These positive results have been controlled with free living porpoises in the Little Belt at the Danish town of Fredericia. Whenever porpoises were seen, PAL started the signal train. The animals were neither attracted nor chased off but very intrigued examined the noise source. Since porpoises do not send signals non-stop, they can miss nets and thus collide with them. PAL will help to avoid this.
The number and volume of clicks, received by a click generator, considerably increased during operation of the warning system. The result confirmed the conclusions of the aquarium in Kerteminde. If the new warning system can indeed help to protect porpoises from drowning in fish nets has to be proven by a field test together with fishermen. The successful prototype is at present adjusted to the harsh conditions of the fishing industry.
