Acoustic trauma with fatal consequences: According to an expert report by the Federal Agency for Nature Conservation, the blasting of sea mines in the Fehmarnbelt probably cost several Baltic harbor porpoises their lives. Conservationists are now calling for improved regulations for underwater explosions. The Bundeswehr has already suspended planned actions in the Baltic Sea. The responsible federal authorities have also set up a joint working group to develop improved measures aimed at protecting the threatened marine mammals.
The sound waves of massive explosions thundered through the underwater world in the Fehmarnbelt nature reserve in August 2019. The reason was the targeted detonation of 42 British sea mines by the German Navy. According to experts, these remnants from World War II represented a threat to shipping. In order to protect the harbor porpoises (Phocoena phocoena) from noise pollution in this region of the sea, the usual deterrent measures were carried out in advance of the blasts: Smaller underwater blasts Should drive away animals. But after the mine blasts, the suspicion arose that this measure had not worked. Dead porpoises are found all year round on German seashores. But in the period from the end of August to the end of November 2019, the number of deaths found on the Schleswig-Holstein Baltic Sea coast was 41 animals, higher than the average in previous years.
Torn hearing organs
The Federal Agency for Nature Conservation then initiated an investigation: some of the dead porpoises were autopsied by the University of Veterinary Medicine in Hanover in order to find out the causes of death. In addition, measurements of the sound levels during the underwater explosions were analyzed and indications of the presence of harbor porpoises were recorded. For this purpose, experts evaluated recordings of echolocation sounds in the Fehmarnbelt nature reserve.
The results of the investigations show that despite the deterrence measures at the time of the blasting, harbor porpoises were in the hazard area. They also show that the sound pressure of the blasts was so high in almost the entire protected area that the sensitive hearing system of the marine mammals could be damaged. The autopsies of the dead finds also showed: One third of the 24 examined animals had injuries to the hearing organs, which were caused by extremely loud impulse sound events, such as those typically caused by explosions. Since the animals rely on their hearing for their navigation and communication, such acoustic trauma is a death sentence for them, experts say.
Consequences required
According to the opinion of the Federal Agency for Nature Conservation, it cannot be ruled out that other underwater explosions also led to the dead finds with acoustic trauma. But the connection with the mine blasting at the end of August is obvious. The nature conservation organization NABU is convinced of this cause and accuses the German Navy of not paying sufficient attention to the endangerment of the threatened underwater mammals. “The German Navy must draw conclusions and fundamentally rethink its attitude towards nature and species protection. This also applies to the mandatory implementation of environmental impact assessments prior to unavoidable explosions, ”says Jörg-Andreas Krüger from NABU. The NABU appeals to the federal government to provide the necessary structures and financial resources for the strategic and environmentally friendly recovery of old ammunition. “We urgently need a national strategy for dealing with the dangerous World War II heritage at the bottom of the North and Baltic Seas,” writes NABU.
In order to better protect the endangered harbor porpoises, the Federal Ministries for the Environment, Defense and Transport have already set up a working group headed by the Federal Agency for Nature Conservation. Its aim is to develop guidelines for the removal of old munitions in the North and Baltic Seas. As the Federal Ministry for the Environment emphasizes, in some cases targeted demolitions of sea mines seem inevitable for safety reasons. The aim is therefore to take measures to reduce the risk to the environment to a minimum.
For example, the working group is supposed to develop guidelines that ensure that blasting is only carried out outside of times when harbor porpoises are often in the affected area, reproduce or raise their young. The potential of technical protective measures should also be checked again. For example, the use of so-called bubble curtains around a point of explosion could reduce the spread of sound. It should also be explored to what extent the use of acoustic deterrent technology can be improved in order to scare harbor porpoises away at least from the immediate vicinity of the blasting sites.
Source: Federal Ministry for the Environment, Nature Conservation and Nuclear Safety, Federal Agency for Nature Conservation, NABU
BMU / BfN on the investigation reports:
https://www.bfn.de/themen/meeresnaturschutz.html