Estimated at-sea Distribution of Grey and Harbour Seals - updated maps 2017

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.ReferencesJones, 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

These maps are an update of the previous seal usage maps described in Jones et al. (2015). There are three key updates: (1) The telemetry data have been updated and now include data from 1991 - 2016 (inclusive) resulting in a marked increase (grey seals: 23%; harbour seals: 39%) in sample size for the UK; (2) The count data now include effort data and have been updated resulting in estimates of usage scaled to the estimated population size in 2015; (3) Haulout sites have been clustered together resulting in an increase in the proportion of sites for which there are associated telemetry data and thus increased accuracy of estimated distribution. The estimates reflect the expected mean number of seals in each 5 x 5 km cell at any given time. The estimates do not distinguish between the type of usage (e.g. foraging or travelling behaviour) and similar usage values could be a result of many individuals using a given area a small amount, or a small number of individuals that area intensively. Temporal variation in usage (seasonally or annually) is not represented. The confidence intervals reflect confidence in the estimate of mean usage in each cell, rather than showing the variability in usage. Thus, the confidence intervals are per cell and so do not represent uncertainty in distribution across the maps. Telemetry data were aggregated in order to provide the most complete spatio-temporal coverage around the UK, thus any differences in distribution by sex or age are not reflected. These maps only reflect estimates of usage resulting from seals that haul out in the UK and the Republic of Ireland; usage emanating from continental Europe is not considered.