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Baltic Sea Harbour porpoise foraging habitats

New report details the foraging habits of Harbour porpoises in the Baltic Sea. The report is based on a study done by scientist from DCE – Danish Centre for Environment and Energy from 2010-2015.

A pod of porpoise in the open sea (Photo: Colourbox)

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 the International Union for Conservation of Nature (IUCN). The harbour porpoise is protected by the Habitats Directive. This means that a system of strict protection shall be established throughout the species natural range, and that sites of significant importance to the species should be designated and protected.

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 this project (the SAMBAH project).

The project was a five-year study with 304 passive acoustic dataloggers deployed for two consecutive years, from May 2011 to April 2013, comprising a very large dataset for examining whether buzzes may be used to designate foraging habitats. The acoustic data were analysed in accordance with the scientist posed hypothesize: That the proportion of buzzes would vary between stations and in time, indicating that some areas and times of the day and/or times of the year are more important than others, in terms of foraging.

Based on the gathered data from 2011 to 2013 the scientists showed that the feeding ratio for harbour porpoises was higher in the Baltic Proper than in the Southwest Baltic. It also shows that in the entire study area, the feeding buzz ratio was significantly higher during dawn and night than during the day and dusk. The scientists 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 in places where they can feed.

The results underline that harbour porpoises are rightly 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.

In conclusion this means that, in order to increase the chances of a positive development for the critically endangered harbour porpoise population in the Baltic Proper, management plans with actual conservation measures should be implemented in the designated Natura 2000 sites.

Read the full report here

For more information, please contact Line A. Kyhn

E-mail: lky@bios.au.dk