Sounds are essential for marine animals

The life of marine animals is largely based on the exploitation of the underwater soundscape. Noise disturbs their lives. Sounds of human origin cause stress to marine animals. In addition, loud noises endanger their health.

Animals in the Baltic Sea compensate for the poor visibility by utilising the soundscape

In the Baltic Sea, the amount of sunlight penetrating the depths is reduced by the water turbidity, the low elevation of the sun, as well as the snow-covered ice sheet in winter. These factors can reduce the underwater visibility to only a few metres. By contrast, sound transmits well in water. Depending on their frequency, some sounds can travel underwater for tens of kilometres.

The importance of sound in the underwater world can be compared to that of light on the surface of the earth. Sounds are important to many marine animals, for example in communication, reproduction, seeking food, and orientation.

The seals of the Baltic Sea communicate using sounds. The only whale species in the Baltic Sea, i.e. the harbour porpoise, makes the most advanced use of sound and can explore its underwater environment using a type of natural sonar. On the other hand, the seal species in the Baltic Sea collect information about their environment through careful listening.

Although the harbour porpoise is best able to sense high-pitched sounds, noise from shipping traffic has also been shown to cause interference. The hearing range of fish is generally the same as that of humans, and their behaviour can be affected by ship noise. However, there are many species-specific differences in response to noise disturbance.

Man-made noise interferes with the daily life of marine animals

The volume and range of anthropogenic sounds are often greater than those of natural sounds. Human-generated sounds have been found to have harmful effects on marine animals.

Depending on the volume of the sound and the proximity of the animal, anthropogenic noise can cause behavioural changes, an elevation of the hearing threshold, damage to the hearing organs, physical injury or even sudden death. The worst noises are sudden and short-lived, such as blasting and pile-driving.

Even if man-made noises do not have significant consequences for the animal, they reduce their hearing-based living space. In other words, they reduce the area in which an animal can register sounds that are meaningful to its life.

This space always decreases whenever anthropogenic noise is louder than natural sounds. In such cases, e.g. communication, the avoidance of predators, and the detection of prey become more difficult for marine animals.

Moreover, noise causes stress in marine animals. Although the link between noise and stress is obvious in humans, now it has been found in fish and whales also. For example, the effects of physical stress caused by harmful substances are exacerbated by noise-induced stress.