Use of haul-out sites by grey and harbour seals in Dublin Bay and adjacent coastal waters

abstract: Haul-out sites enable seals to carry out essential functions such as resting, pupping and moulting. Knowledge of the location and use of these sites is important for conservation management to ensure they remain available and undisturbed during key times of the year. This survey recorded the use of haul-out sites close to Dublin Port during a time of increased construction activity to assess whether infrastructural development impacted on seals during pupping and moulting seasons. A total of 10 seal haul-out sites in Dublin Bay and adjacent coastal waters were surveyed on 16 days between 30 June 2023 and 18 January 2024. Most sites were surveyed with an unmanned aerial vehicle (UAV). Overall, grey seals were more abundant than harbour seals, with maximum counts of 326 in October and 300 in July and a minimum of 167 in November. Harbour seal numbers ranged from 117 to 5, with a peak in July. Most grey seals were recorded on Dalkey Island, Lambay Island and St Patrick's Island and on Ireland's Eye, while most harbour seals were observed at Rush Head and on Lambay Island and North Bull Island, with small numbers recorded at Sandycove. The same haul-out sites were used consistently throughout the survey period and are consistent with previous studies suggesting no changes in the use of haul-out sites. The count totals presented here are consistent with the results of the most recent national monitoring programme for seals in this area. A total of 88 grey seal pups were recorded in October on Lambay Island and St Patrick's Island and on Ireland's Eye and 33 harbour seal pups in July. In January concentrations of grey seals were recorded on Lambay Island (88) and St Patrick's Island (85) off Skerries during the moult period. The efficient use of UAVs for surveys of haul-out sites, with minimal disturbance to seals, is demonstrated and recommended as a cost-effective tool for regular monitoring seals at haul out sites in the future.