Common/harbour seal (Phoca vitulina) - mean percentage at-sea population per 25 km (Carter et al 2022)
These shapefiles are estimates of seal distribution on a 5 km x 5 km grid covering the maximum foraging range of seals from haulouts in the UK and Ireland.
IMPORTANT NOTE
These estimates represent predicted seal distribution from haulouts in the UK and Ireland only and do not account for density of seals from haulouts elsewhere.
INTERPRETATION
For each species, three seal distribution surfaces are provided: mean and associated lower and upper 95% confidence limits. (only mean is depicted on NMPi)
For each cell, the confidence intervals represent the range of values within which, based onmthe underlying model, the true seal density is likely encompassed. The mean represents the a measure of the centre of this range.
The surfaces are provided as relative density.
For each cell, the value given represents the percentage of the UK and Ireland at-sea population (or SAC at-sea population for SAC-specific estimates) - i.e. excluding hauled-out animals - estimated to be present at any one time during the main foraging season (see below for information on temporal relevance).
Cells in the mean distribution surface sum to 100%. Thus, cell values can be summed across an area. For example, to estimate the total abundance of seals in an area of interest, it is possible to sum all cells in the mean distribution surface that fall within that area.
However, confidence interval estimates are provided on a cell-wise basis. Therefore, the sum of all cells in the lower confidence interval surface will be less than 100%, and the sum of all cells in the upper confidence interval surface will be greater than 100%. Cells in the confidence limit surfaces therefore CANNOT be summed across an area, and must be treated on a cell-by-cell basis. Summing these values across an area would give inflated confidence intervals.
TEMPORAL RELEVANCE
These estimates of seal density are generated using telemetry data from the main foraging season for each species, thus the distribution maps represent seal density during the main foraging season (grey seals: summer, harbour seals: spring).
Density estimates were spatially weighted using the most recent population count available per haulout. The majority of counts were from 2018, and 94.4% were from 2015 onwards.
Density estimates were predicted using environmental data from 2018. Thus, the density estimates represent relative seal density during the main foraging season in 2018.
CONSIDERATIONS AND EXCLUSIONS
Density estimates are given as relative density, rather than absolute density (i.e. number of animals) due to caveats relating to population scalars required to convert between the two. For detailed information on scaling from relative to absolute density, see Supplementary Material S7.4 in the manuscript Carter et al. (2022).
Confidence intervals do not account for uncertainty relating to individual variation in habitat preference or temporal changes in abundance (e.g. throughout the day).
Estimates for the following areas should be treated with caution as they may contain a high degree of un-modelled uncertainty due to lack of recent telemetry data, or paucity of environmental data:
-Shetland (grey and harbour seals)
-East Coast (grey and harbour seals)
-English Channel (harbour seals)
-Cornwall and Isles of Scilly (grey seals)
-Celtic Sea and Irish Sea South (harbour seals)
-West Ireland (harbour seals)