Estimating the abundance of the critically endangered Baltic Proper harbour porpoise (Phocoena phocoena) population using passive acoustic monitoring

Mats Amundin, Julia Carlström, Len Thomas, Ida Carlén, Jonas Teilmann, Jakob Tougaard, Olli Loisa, Line A. Kyhn, Signe Sveegaard, M. Louise Burt, Iwona Pawliczka, Radomil Koza, Bartlomiej Arciszewski, Anders Galatius, Jussi Laaksonlaita, Jamie Macauley, Andrew J. Wright, Anja Gallus, Michael Dähne, Alejandro Acevedo‐gutiérrezHarald Benke, Jens Koblitz, Nick Tregenza, Daniel Wennerberg, Katharina Brundiers, Monika Kosecka, Cinthia Tiberi Ljungqvist, Ivar Jussi, Martin Jabbusch, Sami Lyytinen, Aleksej Šaškov, Penina Blankett

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Knowing the abundance of a population is a crucial component to assess its conservation status and develop effective conservation plans. For most cetaceans, abundance estimation is difficult given their cryptic and mobile nature, especially when the population is small and has a transnational distribution. In the Baltic Sea, the number of harbour porpoises (Phocoena phocoena) has collapsed since the mid-20th century and the Baltic Proper harbour porpoise is listed as Critically Endangered by the IUCN and HELCOM; however, its abundance remains unknown. Here, one of the largest ever passive acoustic monitoring studies was carried out by eight Baltic Sea nations to estimate the abundance of the Baltic Proper harbour porpoise for the first time. By logging porpoise echolocation signals at 298 stations during May 2011–April 2013, calibrating the loggers’ spatial detection performance at sea, and measuring the click rate of tagged individuals, we estimated an abundance of 71–1105 individuals (95% CI, point estimate 491) during May–October within the population's proposed management border. The small abundance estimate strongly supports that the Baltic Proper harbour porpoise is facing an extremely high risk of extinction, and highlights the need for immediate and efficient conservation actions through international cooperation. It also provides a starting point in monitoring the trend of the population abundance to evaluate the effectiveness of management measures and determine its interactions with the larger neighboring Belt Sea population. Further, we offer evidence that design-based passive acoustic monitoring can generate reliable estimates of the abundance of rare and cryptic animal populations across large spatial scales.
Original languageEnglish
Article numbere8554
Number of pages39
JournalEcology and Evolution
Issue number2
Publication statusPublished - 19 Feb 2022


  • abundance estimation
  • C-POD
  • detection function
  • passive acoustic monitoring
  • Phocoena phocoena


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