It is absolutely vital for whales to perceive their environment acoustically because they use their ears to “see”. If acoustic signals are masked, their “field of vision” is reduced and it can harm the biological fitness (physical and mental condition) of marine mammals such as the blue whale and fin whale. Nowadays man-made underwater noise is a virtually constant reality in all oceans. Shipping traffic is a source of chronic noise which has a high “masking potential”. Masking means an overlapping of sound signals. An intended signal of communication between marine mammals is covered up, or acoustically masked, by an interfering signal. Such interfering signals come from airguns which are used to explore the ocean floor. These signals are much louder and often much shorter than typical ship noise. It has long been suspected that these loud seismic signals can damage the hearing of marine mammals since these sound bursts can be 1,000 times louder than a ship. Underwater noise can also interfere with communication between marine mammals and their perception of other sounds in their environment. Whales depend on these signals, for example to find food or a mate.
The new UBA study shows that airgun signals can have an impact at distances of up to at least 2,000 kilometres (km). This can affect animals living within the Antarctic Specially Protected Areas located south of 60° south, even airguns are in use on ships located north of 60° latitude. Airgun signals can evolve into intermittent noise with high masking potential already at medium distances of 500 to 1,000 km. At distances of over 1,000 km the airgun bursts can develop into continuous noise. This results in a loss of the natural communication distance of blue and fin whales in Antarctica, reducing it to about one per cent of its original range.
The results of the UBA study show that masking effects and significant impact on the vocalisations of animals are possible across great distances and must be taken into consideration in the environmental impact assessment of impulsive sound sources like airguns. The model in this project will be further developed in a follow-up project which will enable applicability to other habitats. These habitats include the Arctic, which is expected to experience a lot of use of airguns to image the ocean floor for mineral resources and for research purposes. UBA's President Maria Krautzberger said: "We must know exactly what the effects of sound waves from airguns are on marine mammals and take this into account in the environmental assessment of marine research. We therefore need an international noise action plan, perhaps in the framework of the Antarctic Treaty System."
The German Federal Ministry for Environment put into force a noise action plan for the North Sea on 1 December 2013. It enables the sustainable development of offshore wind power in Germany. The aim is to protect the native porpoise against noise, in particular when rearing its young. Noise is caused when foundation piles for wind turbines are driven into the seabed.
Complete report on UBA study Assessment of potential for masking in marine mammals of the Antarctic exposed to underwater sound from airguns
The airguns used for underground exploration are essentially metal cylinders charged with high-pressure air which is then fired in bursts similar to an explosion. The burst creates an air bubble which generates a very short but very loud sound signal. Most of the acoustic signals emitted from airguns are in the low frequency range of up to 300 Hertz, making an overlap with the sounds and vocalisations of whales and seals probable. The baleen, blue and fin whale common to the Antarctic Sea communicate by and large in this frequency range.
Research project: Acoustic masking by airguns
The UBA study modelled the sound propagation of airgun signals at distances of 100, 500, 1,000 and 2,000 km. Short, low-frequency sound signals can become constant acoustic signals over long distances, and this has a very high masking potential. The modelled signals were overlaid with the vocalisations of the fin whale, blue whale and the Weddell seal to assess the distances over which communication masking could occur and thus reduce communication distances. Signals were analysed using a leaky integrator within the bandwidth of the modelled vocalisations of the Weddell seal, blue whale and fin whale.
This UBA study shows that the long-range effects of underwater noise should not be underestimated: although many questions remain unanswered, the study results indicate that impulse airgun signals very likely result in masking and a population effect cannot be ruled out. These findings must be taken into account in the evaluation of the potential environmental impact of impulse sound sources such as airguns.