Trends in seal abundance and grey seal pup production

Scotland and eastern England (SMUs 1-9) hold the majority of the UK populations of grey and harbour seals. The key method of monitoring harbour seal trends in these areas are through aerial survey counts during their August moult (covering all areas in a 5-year cycle). Estimates of harbour trends are essential for effective conservation and management. Such estimates based on data up until 2017 were provided in Thompson et al. (2019). An update of these estimates is required, especially given the recent low counts in harbour seals in the Southeast England Sea Management Unit (SMU) which had previously been the only large SMU showing a sustained increases in abundance. For grey seals, population estimates and trends in grey seal abundance are estimated within an age specific population dynamics model (Thomas 2021) using data from four regions: Inner & Outer Hebrides, Orkney, and North Sea; the first three regions are equivalent to the West Scotland, Western Isles and North Coast & Orkney SMUs respectively, and the North Sea region is an aggregation of East Scotland, Northeast & Southeast England SMUs. The data considered in the population model are pup production estimates from regularly monitored breeding colonies and independent estimates of population size. These independent estimates are generated using grey seal count data from August surveys and a telemetry-derived scalar to account for seals not hauled out during surveys, and are termed independent because they are independent from those derived from pup production data. The population model provides population estimates on the scale of the four regions and is based on the distribution during the breeding season. It is critical to understand spatial variation in abundance and trends therein, on an SMU scale, during the foraging season (the majority of the year) which is when seals are most likely to be impacted at-sea processes (e.g. anthropogenic activities, prey availability), and also when they are most likely to impact harbour seals. In addition, an analyses of pup production data is required for an understanding of trends for SMUs and trends in the context of SACs while accounting for, and quantifying, the jump in pup production associated with the change in survey methods (film to digital). Here we fit trends to the available data for the above-described three metrics (harbour and grey seal August counts, and grey seal pup production) by Seal Management Unit (SMU). As well as illustrating these trends, we overlay the relevant counts/production estimates for Special Areas of Conservation (SACs). In addition, we use the August grey seal count data to generate a third independent estimate for use in the population model (Thomas et al. 2021), as well as adjusting the second and third estimate (using an updated scalar; Russell & Carter 2021). Finally, we combine trends in August counts of grey seals across SMUs to provide a single trend in counts for SMUs 1-9, and highlight the potential future utility of such a prediction. The results in this BP are a preliminary extension of the analyses currently being conducted for the upcoming OSPAR Assessment.