Seal Usage Maps

The estimation of mean seal usage (and the corresponding uncertainty) is an involved process. The resulting maps should be interpreted with care. The aim of the report is to inform the end user of both the strengths and limitations of the approach and the output maps.

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 using 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.