These GIS files (UTM zone 30N WGS84 Shapefiles and GeoTIFFs) of gridded harbour (Phoca vitulina) and grey (Halichoerus grypus) seal at-sea (i.e. marine) and total (i.e. marine and haul out combined) usage estimates were produced for Marine Scotland (Marine Mammal Scientific Support Research Programme MMSS/002/15) by the Sea Mammal Research Unit (SMRU). An R-based modelling process was used to combine seal telemetry data (270 grey seals and 330 harbour seals tagged in the UK) and terrestrial count data (UK and Republic of Ireland) to produce estimated usage and associated 95% confidence intervals. These predictions can be interpreted as the average number of seals in each 5 x 5 km grid cell at any point in time. The kernel smoothing used to change the telemetry point locations to a usage surface can create at-sea usage inland, so to accurately sum usage in an area, ensure that all local onshore and offshore grid cells are summed. The telemetry data for the seals were obtained from SMRU Instrumentation Satellite Relay Data Loggers (SRDL) and Fastloc© GPS GSM â??phoneâ? tags deployed over the years 1991 to 2016. Locations were processed through a set of data-cleansing protocols to remove null and missing values and any duplicated records. The SRDL positional error was corrected using a Kalman filter and data were used to estimate positions at two-hourly intervals. The majority of GPS locations have an expected error of = 55 m; occasional outliers were excluded using thresholds of residual error and number of satellites, and then straight-line interpolated to regularise to the same two-hourly intervals as the SRDL data. The terrestrial count data were collected by either ground or aerial survey. The aerial surveys were carried out by SMRU during August. During such surveys, all seals along a specified coastline are counted and their coordinates recorded to an accuracy of approximately 50 m. Surveys take place within two hours of low tide when low tide is between 12:00 and 18:00 hours. Survey effort was variable between locations. Surveyed coastline was gridded to 5 x 5 km and cells that were surveyed but in which no animals were located were given a value of 0. Full details on the methodology used to produce the usage estimates are given in Jones et al. (2015). Details of the updates are given in report associated with these files. References Jones, E.L., McConnell, B.J., Smout, S.C., Hammond, P.S., Duck, C.D., Morris, C., Thompson, D., Russell, D.J.F., Vincent, C., Cronin, M., Sharples, R.J. and Matthiopoulos, J. (2015) Patterns of space use in sympatric marine colonial predators reveals scales of spatial partitioning. Marine Ecology Progress Series, 534, p. 235-249. DOI: 10.3354/meps11370