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Cetacean passive acoustic network

A passive acoustic hydrophone network has been put into operation to record the presence of porpoises and dolphins in the Belgian part of the North Sea (BPNS).

Scientific background

Porpoises and dolphins (Odontoceti) use echolocation to extract information from their surroundings. Dolphins produce clicks in a wide frequency range and are typically short and loud while porpoises are producing longer and weaker clicks in a narrow frequency range (120 - 145 kHz, mode 132 kHz). These clicks can be recorded by the passive acoustic device, C-POD (Chelonia Limited, figure below left), when a marine mammal is swimming in the vicinity of the recorder. The C-POD can record clicks between 20 and 160 kHz including ambient background noise, sonar and other biotic underwater sound. The key to the performance of the C-POD is detection and classification of series of clicks, so-called click trains. Click trains have distinctive features which are used by the classification algorithms to identify the occurring cetacean species.



Left: Example of a click train of harbour porpoise (Phocoena phocoena) - Right: Harbour porpoise (©Kustfotografie.be/Misjel Decleer)



The development of a permanent network of C-PODs in the BPNS, as part of the marine LifeWatch observatory, started in 2014. Ten C-PODs are now continuously deployed on tripod frames positioned along an east-west gradient covering coastal, midshore and offshore zones of the BPNS. The C-POD itself is attached to a buoy with an an acoustic release system (Vemco VR2AR), allowing for the recovery of the equipment. Before 2018, C-PODs were connected to navigation buoys or anchored to ship wrecks or to artificial hard structures .


Left: C-POD attached to a tripod frame with an acoustic release system (©VLIZ); Right: Location of the 10 C-PODs in the Belgian Part of the North Sea (situation December 2018)



Data can be accessed via the LifeWatch Data Explorer for marine mammals data.

Metadata is available at:

  • LifeWatch observatory data: passive acoustic network (CPOD) for Cetacean detection, More


Useful links

  • CPOD Data Analysis Workshop: Learn from the findings of the 2017 LifeWatch Data Analysis workshop for the cetacean passive acoustic network.


Most recent publications

  • Augustijns, T. (2018). Harbour porpoises in the Belgian Part of the North Sea: Using passive acoustic monitoring to determine spatio-temporal patterns in distribution and feeding behaviour. MSc Thesis. Faculty of Sciences, Biology Department, Research Group Marine Biology: Gent. 47 pp. [link to IMIS record]
  • Buyse, J. (2018). Monitoring of harbour porpoise (Phocoena phocoena) density in the Belgian part of the North Sea using aerial surveys and passive acoustic monitoring. MSc Thesis. Oceans & Lakes, Interuniversity Master in Marine and Lacustrine Science and Management: Antwerpen, Gent and Brussel. 13 [Literature review] + 32 [Manuscript] pp. [link to IMIS record]