At least 85,000 porpoise are swimming in the Dutch part of the North Sea, according to researchers at the Imares Wageningen institute.

Nevertheless this is likely to mean more have moved into Dutch waters in search of food than that the total North Sea population has increased, researcher Steve Geelhoed told Trouw on Tuesday.

The rise in numbers can also be seen in the number of porpoise washed up on Dutch beaches – 517 so far this year. In 2003, just 153 porpoises were found.

Sound

Fisherman have also reported noticing an increase, Derk Jan Berends of the Dutch fisherman’s association told Trouw.

The population shift means porpoise are more likely to be disturbed by human activity such as underwater seismic research and the development of offshore wind turbine farms.

‘Porpoise use sound, a sort of sonar, to find their way and to find food,’Geelhoed said. ‘Human activity disturbs this.’

The fishing industry is currently experimenting with ‘pingers’ which emit a sound to try to stop porpoise becoming entangled with nets. These could also be used to keep them away from wind farm locations, Geelhoed said.