Passive acoustic monitoring of harbour porpoises (PAM)

PAM is routinely applied in impact studies.  Since the construction of the first Dutch offshore wind farm, PAM has been successfully implemented in several monitoring programmes for offshore wind farms in the Dutch North Sea. Converting the number of echolocation clicks of marine mammals into the number of individuals is not yet possible. 

How does the system work?

Harbour porpoises continuously emit clicks used for echolocation to detect prey, orient themselves, and – to a lesser extent – communicate. PAM can record these sounds: it consists of fully automated, static, passive monitoring systems that recognise click trains from harbour porpoises, dolphins and other toothed whales. PAM can be deployed in various environments and for multiple purposes.

Although current PAM devices have a small spatial range (radius <300 metres), the major advantage is that they can collect data continuously for several months. In the North Sea, CPODs or FPODs are installed at designated locations by a Rijkswaterstaat vessel. To prevent collisions with the equipment, they are attached to a structure with large, conspicuous buoys. PAM data are collected on memory cards over a period of about four to six months. A CPOD or FPOD can be quickly retrieved and checked at sea.

Application

PAM is used in studies assessing the effects of human activities on harbour porpoises, such as in offshore wind farms and during harbour construction works. It is also highly valuable for policy-supporting research into porpoise presence. By deploying PAM devices in a systematic pattern within a study area, the habitat use and behaviour of harbour porpoises can be determined. A relatively new application is the detection of so-called ‘feeding buzzes’, which enables the quantification of foraging behaviour.