Several species of bats in northern Europe undertake seasonal migrations between their summer roosts and wintering areas. Doing so, they are known to cross open sea in some cases. Taking account of the increase of wind farms in the Belgian part of the North Sea and the entire North Sea, the lack of information on the spatio-temporal distribution of bats in Belgian waters and the results of some studies (onshore) demonstrating wind turbines can cause high mortalities in bats, a taxon in global decline, it is important to quantify the risk of offshore wind farms in the North Sea to threaten bat populations. To investigate bat distribution, we installed an automated acoustic recorder on the Belgian research vessel ‘Belgica’ to record bats while the vessel is at sea at night. The acoustic detector on the Belgica was operational during 93 nights in autumn 2014 and spring 2015, hence covering two full bat migration periods. In autumn 2014, 117 call sequences were registered in the BPNS, belonging to four different species. In spring 2015, only four sequences were registered, all during one night. The few recordings were all registered during only three nights. These results are not sufficient to solidly determine spatio-temporal patterns of bats in the BPNS, but allow drawing some preliminary conclusions on their frequency of occurrence and distribution at sea. In 2015 and 2016, a network of nine Batcorders is collecting data in the Dutch and Belgian part of the North Sea and along the coastline. This detector network will increase our knowledge about the impact of offshore wind farms on bats as it will increase the number of detections of bats at sea and will allow direct comparison between data collected at the different locations, without seasonal or meteorological bias. This will allow addressing the question if bats are attracted to or avoid offshore wind farms. This may then lead to appropriate management or mitigation measures.

Open Access

North Sea, Environmental Monitoring