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 (>95% of each species). The main method for monitoring harbour seal populations, both in the UK and elsewhere, is through surveys on land during their annual moult (August in the UK). UK grey seal abundance and trends are primarily monitored through a combination August haul out counts and pup production estimates. For both species, abundance levels and national trends, are assessed on the basis of the latest composite (multi year) August counts (SCOS BP 25/01), and for grey seals, pup production estimates (SCOS 25/02). Estimates of trends in abundance for key SMUs, and their encompassed SACs, are essential for effective conservation and management. To assess trends on a SMU and SAC scale, counts/production estimates from individual surveys are used as much as possible, maximising the data available; these counts are input into statistical models to generate trends. For grey seals, pup production and August counts should be considered in combination, as the former represents a powerful and consistent way to evaluate trends, and the latter represents where seal acquire their resources. The trends have been updated (compared to SCOS 2024) for August counts in SMUs 1-3 (western Scotland) and for grey seal pups in SMUs 7-9; East Scotland SMU and eastern England SMUs). For August count data, at least three models were considered with regard to year; no trend, an exponential trend, and a nonlinear (smooth) trend. In addition, for harbour seals in SMUs 4-9, step changes in abundance and trends around 2002 were offered. For harbour seals, an additional model was fit for western Scotland SMUs (not fit in SCOS BP 24/03). For grey seal pup production, the previously quantified impact of the change in method (film to digital aerial surveys in Scottish SMUs, and ground to digital aerial surveys for Eastern English SMUs) was accounted for. The new estimates for 2023 (eastern England) were based on a new camera system (Phase One). For both species SAC trends were generally less favourable than for the SMU that encompassed them. For harbour seals, with the exception of Southwest Scotland (predicted to be stable), all SMUs for which there are notable numbers (SMUs 1-7, and 9) abundance was predicted to be declining and/or depleted. It should be noted that the most recent survey data for SMUs 5 & 6 are now over 5 years old (2019). Grey seal abundance (August counts and pup production) either showed no trend or was increasing in all SMUs (with the potential exception of Shetland). Pup production in West Scotland and Western Isles was increasing and at an all-time high after a long period of stability. In Southwest Scotland (where < 10 pups are born annually) and West Scotland SMUs, summer abundance was also predicted to be increasing. In contrast, August counts in the Western Isles are variable but showed no apparent trend. Pup production and August counts (latest data 2019) in North Coast and Orkney were stable. For Shetland, there was an indication of a decline in pup production but August counts showed no trend. In all east coast SMUs (SMUs 6-9) pup production was predicted to be increasing. The August counts were stable for the Moray Firth and East Scotland, but increasing in eastern England.