Photo-ID Analysis of Harbour Porpoises in the Eastern Scheldt: Insights, Patterns, and Conservation

Abstract

The "Photo-ID Analysis of Harbour Porpoises in the Eastern Scheldt” thesis project with Stichting Rugvin represents a comprehensive and long-term investigation into the individual harbour porpoises residing there. The project initially began ad hoc in 2010 and has evolved into a structured and dedicated research endeavour, spanning from 2015 to 2023. The study involves the systematic documentation of 92 recognized harbour porpoises, including both long-standing and recently identified individuals. This project hinges on the extensive collection of photographs and associated GPS data, resulting in a large dataset.

The research seeks to understand the environmental factors, such as tidal status, bathymetry, and prey availability that impact the distribution and behaviour of porpoises. The study utilised Photo-ID techniques to track individual porpoises, allowing for the analysis of their movement patterns and social dynamics using their unique markings. GIS mapping provides additional clarity on the spatial preferences of these marine mammals, specifically identifying important areas, the hotspots of high population density, within the Eastern Scheldt where they engage in activities such as foraging, socialising, travelling and mating.

The results suggest that harbour porpoises demonstrate a preference for deeper waters associated with a depth gradient in the Eastern Scheldt, specifically in areas near the harbours of Zierikzee and Kats, where this gradient causes turbulence in the water, likely influencing the harbour porpoises’ habitat preferences. The research indicates that tidal conditions have minimal impact on harbour porpoise behaviour, but bathymetry is an important variable in determining their foraging locations and social interactions. However, further research is needed to determine if the social interactions convene in these locations out of coincidence due to food source and foraging. The areas near the harbours of Zierikzee and Kats indicates these areas are important to the harbour porpoises’ survival within the Eastern Scheldt, underlining the necessity of targeted conservation strategies to protect these zones.

This study provides valuable information about the ecology of harbour porpoises in the Eastern Scheldt, offering essential data for the development of appropriate conservation strategies. Additionally, it addresses the current lack of information regarding the behaviour and habitat preferences of these marine mammals, providing a foundation for conducting similar research throughout this region.