A report by the Federal Agency for Nature Conservation shows that harbour porpoises are endangered by underwater explosions
The Federal Agency for Nature Conservation (BfN) has published an expert report that describes how detonations of WWII-era naval mines affected harbour porpoises in the Fehmarn Belt nature conservation area in the Baltic Sea in August 2019. The results show that the strictly protected harbour porpoises have been exposed to a high risk of injury from the shock waves of the blasts. To prevent this kind of threat in the future, the Federal Ministries of the Environment, Defence and Transport have set up a joint working group headed up by the Federal Agency for Nature Conservation.
At the end of August 2019, the German navy, which at that time was conducting an exercise with the NATO Mine Countermeasures Group in the adjacent marine area, detonated 42 British naval mines from World War II in the Fehmarn Belt nature conservation area in the Baltic Sea after consulting the competent Water and Shipping Authority. The detonation made it possible to eliminate a threat to human life and health along a busy shipping route. The German navy had carried out its usual deterrence measures in the run-up to the mine explosions. After the detonations became public, the question arose as to whether there is a link between the detonations and the dead harbour porpoises that washed up on the coast. The BfN then commissioned three investigations. They included an evaluation of measurements of sound levels in the Fehmarn Belt nature conservation area at the time of the blasts, an evaluation of measurements of harbour porpoise echolocation sounds around the area at the time of the blasts using click detectors and autopsies of some of the dead harbour porpoises found from the end of August onwards by the University of Veterinary Medicine Hanover to investigate the causes of death.
The findings of the investigations show that harbour porpoises were present in the Fehmarn Belt nature conservation area at the time of the explosions. They also show that the sound exposure level of the blasts was high enough in nearly the entire protected area to injure or kill harbour porpoises.
Dead porpoises are found throughout the year along German coasts. In the period from the end of August to the end of November 2019, 41 dead porpoises were found along the Baltic Sea coast of Schleswig-Holstein, a figure slightly higher than the previous years’ average. It was not possible to perform autopsies on all of the porpoises due to their condition. One third of the 24 porpoises examined showed injuries around the auditory organs caused by extremely loud impulse sound events – usually explosions – which most likely led to their death. However, given the length of the investigation, the deaths resulting from acoustic trauma cannot be clearly attributed to the mine explosions in late August. Other extremely loud impulse sound events – however, these are generally explosions – could also be possible causes.
In order to protect the already endangered harbour porpoise populations more effectively from the impacts of blasts, the Federal Ministries of the Environment, Defence and Transport have set up a joint working group, including representatives from the coastal states and headed up by the Federal Agency for Nature Conservation. The working group aims to develop a joint guideline on nature conservation and legal requirements for the removal of ammunition remanences in the North and Baltic Seas to improve harbour porpoise protection.
Prior to ammunition remanences, an assessment is always carried out to determine whether underwater detonation could be replaced by other measures, e.g. by moving them to shallow water or land where they can be neutralised or detonated. But this is not always possible. Due to the critical condition of some mines or detonators, there is an imminent danger of an unintentional explosion, which was the concern about the mines detonated in August 2019. If explosions are unavoidable in these cases, they are supervised and appropriate mitigation measures taken to protect marine species and habitats. The goal is to keep the impact to a minimum.
The working group is exploring appropriate alternatives for these cases to limit the environmental impact as much as possible. This includes stipulations that prohibit detonations during the periods when harbour porpoises reproduce or raise their offspring. Technical solutions are also being considered to alleviate the effects. For example, so-called bubble curtains can be used to reduce the dispersion of impulsive sound waves. Harbour porpoises can be scared away at least from the immediate vicinity of the blast using acoustic deterrent technology.
The German navy has already responded by procuring deterrent equipment known as "seal scarers".