Abstract
In response to NRW Q1 and Defra Q1, the status of the grey seal population in the southwest UK and
Northern Ireland is examined in this briefing paper. These areas encompass five Seal Management
Units (SMUs): 10. South England, 11. Southwest England, 12. Wales and 13. Northwest England, and
14. Northern Ireland. Data from these SMUs are not included in the population model which is
currently used to estimate grey seal population size. Instead, the estimated proportion of UK pup
production from colonies that are not incorporated in the population model (SMUs 10-14: 3.8 %; non
regularly monitored Scottish colonies: 6.7%) is used to scale the model output to generate a UK grey
seal population estimate. The population model is based on two sets of data: (1) a region-specific
time series of pup production, and (2) overall (i.e. not region-specific) estimates of grey seal
population size from August surveys (hereaft
independent from the pup production data) pertaining to 2008 and 2014. Here the relevant data
from SMUs 10-14 are examined and the feasibility of extending the population model to incorporate
these SMUs is discussed.
Based on available data, it was estimated that current pup production (2019) in SMUs 10-14 is c.
2,900. This, using the most up-to-date data for the rest of the UK (2016-2019 for regularly monitored
colonies), equates to c. 4.4% of UK pup production. There are no SMU-wide recent estimates of pup
production for Wales or Northern Ireland. To generate a robust estimate of pup production in SMU
12, the scalars (used to scale from indicator sites to larger areas) used to estimate pup production
would need to be updated for West Wales (last surveyed in 1994). Although there are time-series of
pup production data from a subset of colonies (e.g. Bardsey Island, Skomer Marine Conservation
Zone, Lundy Island), incorporating these in the population model would require a robust scalar
between such colonies and less regularly monitored colonies, as well as data on August counts.
Indeed, the lack of robust SMU-wide summer haul-out counts for SMUs 11 and 12, is another barrier
to the inclusion of SMUs within the population model. Generating such counts would be challenging
due to the substantial proportion of the population that haul out in caves. In recognition that the
population model does not pertain to a closed population, ideally it should be extended to cover the
whole of the UK (and the northeast Atlantic). However, extending the population model to SMUs 10-
14 would not enhance our understanding of the population in these SMUs, or the UK as a whole.
Northern Ireland is examined in this briefing paper. These areas encompass five Seal Management
Units (SMUs): 10. South England, 11. Southwest England, 12. Wales and 13. Northwest England, and
14. Northern Ireland. Data from these SMUs are not included in the population model which is
currently used to estimate grey seal population size. Instead, the estimated proportion of UK pup
production from colonies that are not incorporated in the population model (SMUs 10-14: 3.8 %; non
regularly monitored Scottish colonies: 6.7%) is used to scale the model output to generate a UK grey
seal population estimate. The population model is based on two sets of data: (1) a region-specific
time series of pup production, and (2) overall (i.e. not region-specific) estimates of grey seal
population size from August surveys (hereaft
independent from the pup production data) pertaining to 2008 and 2014. Here the relevant data
from SMUs 10-14 are examined and the feasibility of extending the population model to incorporate
these SMUs is discussed.
Based on available data, it was estimated that current pup production (2019) in SMUs 10-14 is c.
2,900. This, using the most up-to-date data for the rest of the UK (2016-2019 for regularly monitored
colonies), equates to c. 4.4% of UK pup production. There are no SMU-wide recent estimates of pup
production for Wales or Northern Ireland. To generate a robust estimate of pup production in SMU
12, the scalars (used to scale from indicator sites to larger areas) used to estimate pup production
would need to be updated for West Wales (last surveyed in 1994). Although there are time-series of
pup production data from a subset of colonies (e.g. Bardsey Island, Skomer Marine Conservation
Zone, Lundy Island), incorporating these in the population model would require a robust scalar
between such colonies and less regularly monitored colonies, as well as data on August counts.
Indeed, the lack of robust SMU-wide summer haul-out counts for SMUs 11 and 12, is another barrier
to the inclusion of SMUs within the population model. Generating such counts would be challenging
due to the substantial proportion of the population that haul out in caves. In recognition that the
population model does not pertain to a closed population, ideally it should be extended to cover the
whole of the UK (and the northeast Atlantic). However, extending the population model to SMUs 10-
14 would not enhance our understanding of the population in these SMUs, or the UK as a whole.
| Original language | English |
|---|---|
| Publication status | Published - 2020 |
