Condemned to death; Construction noise kills whales

Offshore wind farms and ship traffic: It's not just underwater noise that disrupts whale communication. They also lose their orientation and die on the beach.

Blue whales can communicate over hundreds of kilometers using their deep calls and sensitive hearing. And even smaller marine mammals such as porpoises use echolocation to find their way around in the habitats they are familiar with. But the increasing construction noise under water, which is particularly the case with new offshore wind farms, could disrupt the sensitive communication of the animals. "Toothed whales and thus small whales trust their acoustic sense much more than their visual sense," says Harald Benke, head of the German Maritime Museum in Stralsund. Sound is conducted five times better in water than in air.

The brisk shipping traffic now ensures a constant, diffuse "background noise" that is perceived by the marine mammals as a permanent hum. This causes stress, says Benke. The experts attribute mass strandings, such as those off the Tasmanian coast in late 2008 and early 2009, when 150 whales died, to underwater noise, among other things. Whale researchers are therefore skeptical about the push of wind energy out to sea. Marine noise and the pressure waves associated with it, such as those that occur during piling work or during the seismic search for natural gas deposits, are now considered to be one of the main dangers for the sensitive animals worldwide.

Focus on noise abatement underwater construction techniques

"Whales whose hearing is disturbed or permanently damaged by noise are sentenced to death because they can no longer orient themselves," warns Benke. Measurements have shown that even at a distance of 80 kilometers from the sound source, the "ramming pressures" are still above the background noise of shipping traffic.

Noise-reducing underwater construction techniques are also a key topic at the European Society for Cetacean Research meeting, which begins March 22 in Stralsund. According to the industry association EWEA (European Wind Energy Association), eight new wind farms with almost 200 offshore turbines were connected to the grid last year in Europe alone. This year 10 are to be added, seven are under construction and another 52 have already been approved. According to the association, almost half of them are in German waters.

"It has been found that pile-driving work in offshore parks - when the foundations are anchored in the seabed - produces very high sound pressure levels under water," says Kristin Blasche from the Federal Maritime and Hydrographic Agency (BSH). A sound forecast must be prepared in advance for each project. The limit is 160 decibels at a distance of 750 meters from the sound source.

So far, there have been hardly any alternatives to ramming. Research is being carried out on new methods. For example, the University of Hanover proposed the use of a so-called bubble curtain for the North Sea wind farm "alpha ventus" off Borkum. Compressed air hoses are laid around the underwater construction site. The rising air forms an acoustic barrier for sound waves, but the process has its limits: "The bubbles are very dependent on the flow, and no all-round coverage can be achieved," explains Blasche. Other methods will therefore be presented at the conference. These include quieter digging techniques such as "vibration ramming" or "shaking".

The BSH requires wind farm builders to ram as quietly as possible and to use state-of-the-art methods. Shortly before construction begins, a "deterrent device" must always be hung in the water to keep porpoises away from the construction site with unpleasant sounds, says Blasche.

But that, too, obviously entails risks. Harbor porpoise expert Benke points to two Danish wind farms. "In the North Sea, the porpoises have returned to their original territory - not in the Baltic Sea." The reasons for this are unknown. The Baltic Sea population of harbor porpoises, which was estimated at 600 animals according to the latest surveys in the mid-1990s, is considered to be particularly endangered.