Saving Porpoises Noisily

It’s an almost daily occurrence at the North Sea.

Harbour porpoises swim unwittingly into the insidious fishing nets that stretch out thousands of kilometres in the water.

The sea mammals get entangled in the nylon mesh, thrash wildly and die a painful death often caused by suffocation.

The fishing nets which are meant to catch codfish, turbots and plaice, frequently end up trapping hapless turtles, dolphins, monk seals and a myriad of other less well-known species.

The harbour porpoise in the North and Baltic Sea remains especially at risk and has been identified by scientists as an endangered species. Experts estimate that of the some 170,000 porpoises in the North Sea, some 7,000 are killed by nets each year.

New alarm device to stop mass killing

In an effort to stop the senseless killing of the harbour porpoises through the so-called "bycatch", the French biologist Geneviève Desportes is now working on an interactive device that sends off an alarm signal to scare off porpoises from swimming into nets.

At a bio-acoustic laboratory in Kerteminde, Denmark, Desportes along with Swedish colleagues experiments on "Freja" and "Eigil" – two harbour porpoises that were found by fishermen in 1997 half-dead in their nets.

For the first time ever the two porpoises now live in a huge trough of icy sea water at the Fjord centre opposite the harbour and are tended to by humans.

The new generation of alarm devices, "Pinger" are as big as beer mugs. They can be attached to the fishing nets and regularly emanate a high beep.

The researchers hope that the fishing nets, which are invisible to the porpoises, will at least be now be audibly present for the mammals.

New devices more intelligent

The alarm devices are not new.

But the ones available so far weren’t practical enough to use, according to the researchers and it was unrealistic to artificially hook up the entire North and Baltic Sea to the alarm.

Another risk was that the porpoises would get used to the beeping of the alarm and that would nullify the desired effect.

The new intelligent "pinger" in contrast only gives out an alarm signal when the harbour porpoises near the dreaded nets.

Researchers also make use of the sonar system, with which the porpoises, much like bats, orient themselves. Hence if a porpoise goes after prey in the water, it gives off signals from its "bio-sonar".

These signals are received by a microphone in the "Pinger" device and it activates the sound.

The device tricks the porpoise by first luring it with an appealing sound, and then as it gets closer to the net, a shrill tone frightens it off. The trick prevents the shrill sound from failing in its desired effect.

Next step the sea

The device has been tried out on the porpoises, or rather guinea pigs, Freja and Eigil.

Researchers are pleased with the results.

The next step is trying out the interactive "Pinger" in the open sea.