The sources of sound in the Norwegian Sea are mostly located relatively close to the Norwegian coast. The Norwegian Sea is exposed to anthropogenic sound from sources such as shipping, fishing vessels, seismic airguns, and military sonars.
In Norwegian waters, the majority of seismic surveys occur in the North Sea, but a number also occur in the Norwegian Sea every year; this is to search for new oil and gas fields, as well as to estimate remaining reserves within existing fields. Sound from seismic air guns are characterized by low frequencies and high sound levels, resulting in sound that under certain circumstances can propagate several thousand kilometres. Furthermore, seismic sound is in the frequency range audible to most fish and marine mammals. This means that not only can surveys within the Norwegian Sea be audible to animals there, but also surveys taking place in the North Sea and Barents Sea. Seismic sound has the potential to disturb both fish and marine mammals.
Sonars are occasionally used in the Norwegian Sea during naval exercises. The only fish species common in the Norwegian Sea that can detect sonar signals, herring, are not negatively affected at individual or population levels. The ways in which sonar signals affect marine mammals in the Norwegian Sea has been studied intensively in the past decade, and various effects such as avoidance, cessation of feeding, and changes in vocalisation and diving have been documented. Out of the mammal species common in the Norwegian Sea, killer whales, minke whales and sperm whales are the most sensitive, while humpback whales and pilot whales are less disturbed by naval sonars. Bottlenose whales (Hyperoodon ampullatus), which are not common in the Norwegian Sea, are the most sensitive of the marine mammal species investigated. Naval exercises with sonar activity are planned to avoid areas and periods of high abundance of marine mammals.
The Norwegian Sea houses at least one major shipping lane (Figure 4). Ship noise is less intense than seismic and sonar noise, but contributes to increasing background noise levels even far from the major shipping lanes due to long range sound propagation at low frequencies. Shipping noise can be detected by, and potentially disturb, both fish and marine mammals.
Offshore wind farms are not yet established in the Norwegian Sea, but there are currently plans for several sites. Such wind farms will increase noise during both the construction and operation phases.
