Estimates of cetacean abundance in the southern north sea in winter 2024 from the SCANS-IV aerial surveys - Rapport final (2025)

SCANS surveys are conducted in summer, with the objective of ensuring optimal surveying conditions; there is limited understanding of species distribution and abundance in other seasons (but see Gilles et al. 2016). Further data collection in seasons other than summer would not only enhance our understanding of seasonal changes in distribution but could also inform the need to adapt management (e.g., management of threats and spatial/temporal protection measures). The Southern North Sea Special Area of Conservation (SAC) for harbour porpoise has been designated in UK waters with an understanding of differing winter and summer distributions which are referenced through seasonal boundaries within the wider SAC. Given the skew of data availability to summer months, it is essential to better understand the seasonality of this region for this species. More information about winter distribution and connectivity with sister SACs in Dutch and German waters is very valuable. 

Therefore, as an extension to SCANS-IV, and to assess the feasibility of conducting surveys during winter, aerial surveys were conducted in the southern North Sea from January to March 2024, designated as winterSCANS.
Concurrently, another survey initiative following the SCANS protocol, the French MAMO survey, was undertaken in the Channel and the data were analysed together.

This is the first time a large-scale systematic survey has been conducted in winter under the SCANS project. The survey provided valuable information on seasonal variation in cetacean distribution and abundance in this area.