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No. 287: BALHAB. Project report to ASCOBANS for the project “Baltic Sea Harbour porpoise foraging habitats (BALHAB)”.

Kyhn, L.A., Carlén, I., Carlström, J. and Tougaard, J. 2018. BALHAB. Project report to ASCOBANS for the project “Baltic Sea Harbour porpoise foraging habitats (BALHAB)”. Aarhus University, DCE – Danish Centre for Environment and Energy, 24 pp. Scientific Report No. 287. http://dce2.au.dk/pub/SR287.pdf


The harbour porpoise (Phocoena phocoena) is the most common cetacean in northern Europe, however, the Baltic Proper sub-population is listed as critically endangered by IUCN (Hammond et al. 2008). The harbour porpoise is protected by the Habitats Directive Annexes II and IV. This means that a system of strict protection (Habitat Directive Article 12) shall be established throughout its natural range (Annex IV), and that sites of significant importance to the species should be designated and protected (Annex II). Preferred foraging habitats may be considered as candidates for special areas of conservation in accordance with the requirements of the Habitat Directive (Annex II). The main purpose of this project was to investigate whether foraging areas for harbour porpoises can be identified by comparing the occurrence of foraging events, i.e. echolocation buzzes, in relation to harbour porpoise presence in the acoustic data from the SAMBAH project – a five-year study with 304 passive acoustic dataloggers deployed for two consecutive years (www.sambah.org). The acoustic data were analysed in accordance with the posed hypothesize; that the proportion of buzzes would vary between stations and in time, indicating that some areas and times of the day/times of the year are more important than others, in terms of foraging.

Extraction of feeding buzzes was automated from the large SAMBAH dataset and based hereon we show that the feeding ratio for harbour porpoises is higher in the Baltic Proper than in the SW Baltic, and that in the entire SAMBAH study area, the feeding buzz ratio is significantly higher during dawn and night than during the day and dusk. We could not identify foraging areas within the high-density areas for harbour porpoises, which supports the theory that porpoises have to feed almost constantly and hence that porpoises occur where they can feed.

Altogether, the results underline that harbour porpoises rightly are placed on the Habitat Directive’s Annex IV, implying that the animals should be protected throughout their distribution range. This may seem to be in conflict with the requirements of Annex II to designate areas of special importance for the species. However, the indications that lead to the conclusion that porpoises are feeding almost continuously must then mean that the most important areas for foraging are also the areas where the densities are highest. It also means that, in order to increase the chances for a positive development of the critically endangered Baltic Proper harbour porpoise population, management plans with actual conservation measures should be implemented in the designated Natura 2000 sites.