Dolphins, fish going deaf from North Sea WWII bomb detonations

Underwater noise caused by humans have many negative effects on submarine wildlife, according to a study done by PhD students in Leiden. For example, the detonation of WWII bombs in the North Sea annually leads to between 800 and 8 thousand cases of permanent hearing damages in porpoises and dolphins, Trouw reports. There are many human activities that, usually unintentionally, cause a cacophony of sounds in the North Sea. These include detonating old bombs, construction for wind farms, series of bangs for seismic research and continuous maritime traffic. Marine mammals with their sonar are extremely sensitive to sound, this was already known. But fish too "hear, experience and interpret" the noise, according to the research by two PhD students at the Institute of Biology Leiden (IBL) of Leiden University. The researchers managed to map to map the noise level of the Dutch North Sea using a number of factors in mathematical models and found quite a cacophony. They then coupled the noise data to behavioral data for porpoises over a number of days on which WWII bombs were detonated. "That gave sufficient evidence to conclude that we can not rule out that individual animals experience disturbances and that influences the population. Permanent or even temporary hearing loss can negatively affect an animal looking for food using sonar", one of the researchers explained to the newspaper. Fish too show visible reactions to sudden and long-continuing noise. The studied fish clearly got a fright when the noise began, diving and tangling with each other - "a clear stress reaction" according to the researchers. The fish seem to get accustomed to the noise after a time, returning to their normal swimming behavior. Though this does not mean there are no harmful effects, for example they are less able to hear predators coming. The researchers call these first conclusions disturbing and potentially far-reaching and believe this subject requires more research. "Cleaning up the old bombs is done from the perspective of safety for people. But if an explosion appears to lead to the avoidance of that place, you can, for instance, tell the EOD to detonate bombs in one specific place. More knowledge can provide better balance for the interests of ecology and economy."