Since the beginning of 2009, porpoises in the Fehmarnbelt have been closely monitored to assess their behaviour and the possible effects that a fixed link across or under the water would have on them. The investigations will continue at least until the end of 2010 and will throw new light on the porpoise population in the area.

“We don’t know the precise numbers, but based on previous surveys there seem to be significantly more porpoises in the Fehmarnbelt than expected,” says Dr Georg Nehls, BioConsult SH. “In the spring of 2009, we sighted no fewer than around 40 animals in just eight hours and again the following autumn, we recorded more porpoises than expected.”

The new findings form part of the environmental investigations prior to the construction of the Fehmarnbelt Fixed Link and may influence the planning of further work.

Artificial reef attracts fish
“If the bridge or tunnel is constructed properly, the noise and vibration nuisance and its  effect on the porpoises can be kept at a level that does not exceed that of normal vessels,” explains Georg Nehls. “It appears that the porpoises have come to terms with the shipping that passes through the waterway today.”

Georg Nehls points out that experience from related projects shows that underwater constructions such as foundations for bridges or tunnels attract fish because they act as artificial reefs. And with the fish come the porpoises. 

Regular visitors or just passing through
Depending on the weather conditions, the porpoises are monitored from land, sea and air and by special underwater microphones which operate in all weather. Between them, these special measuring methods have been instrumental in mapping porpoise life in the area.

The investigations also indicate that there are fewer porpoises in the Fehmarnbelt during the summer than in spring and autumn. This helps explain the animals’ behaviour and whether their migration is seasonal.

“We have two main theories: either the porpoises stay in the Fehmarnbelt all year round or the Fehmarnbelt plays a larger role as a migration route between the Baltic and the North Sea. We don’t yet know the answer to this,” says Georg Nehls.