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Monitoring of harbour porpoise (Phocoena phocoena) density in the Belgian part of the North Sea using aerial surveys and passive acoustic monitoring
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.

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Document type: Dissertation

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    Passive acoustic monitoring (PAM) is used more and more often to track trends in harbour porpoise populations and to study the influences of man-made structures or management plans. PAM has various advantages over aerial surveys, such as its ability to gather information at night and in a continuous matter, while being less dependent on good weather conditions and offering a more cost-effective approach. However, up till now, only indications of relative abundance are available, because detection functions of individual C-POD devices are unknown and single organisms cannot be distinguished from one another based solely on their acoustic characteristics. This study combined the two techniques and showed that acoustic variables from C-POD echolocation recordings are strongly correlated with visual detections of harbour porpoises obtained through well-established line transect sampling techniques. Using this relationship, a regression model was established, based on the acoustic variable of detection positive hours, which explains about 61% in the variation of the dataset. With this model, absolute estimates can be derived from PAM data, if corrections are applied for the availability and perception bias. However, aerial surveys are still necessary, because the model is based on the robustness of the line sampling method used in these surveys and because they can cover the entire area of the BPNS in one survey. The regression model also needs further improvements to be representative for the entire BPNS, such as more data points and the use of only one mooring type, but it can already be used to fill in data gaps and observe finer trends in abundance and distribution. This study is a step between monitoring of harbour porpoise density solely based on line transect sampling and a fully operational passive acoustic network that can be used to obtain direct absolute density estimates.

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