Updated grey seal (Halichoerus grypus) usage maps in the North Sea

Currently, little is known about the at-sea distribution of grey seals (Halichoerus grypus) which haul out on the UK coast of the southern North Sea, particularly following the large increases in breeding and foraging populations in the area over the last decade. To address this, DECC funded the deployment of 21 telemetry tags on grey seals hauled out on the south-east coast of England in 2015. Historic telemetry from 1991-2011 and population data from 1998-2012 have previously been used to estimate total (at-sea and hauled out) and at-sea distributions of grey seals in the North Sea to support spatial planning.In this study, data from the most recent telemetry tags and population data were incorporated to provide updated maps of usage in the North Sea. This included data from the 21 tags deployed in south-east England in 2015 and four tags deployed on the east coast of Scotland in 2013. In total, grey seal movement data comprising 175 telemetry tags from 1991-2015 were combined with population estimates for 2014. Population-level species distribution maps and associated confidence intervals were produced at a resolution of 5 km x 5 km. These maps provide the best current estimate of grey seal usage in the North Sea by animals from UK haulout sites. This report describes how usage maps have been updated using contemporary data and revised methodology to provide the best estimate of distribution scaled to 2014 population estimates with associated uncertainty.