<>North Bull Island Seal Survey

The Irish Whale and Dolphin Group conducted a seal survey on North Bull Island, here are their findings.

North Bull Island is a unique site in Co. Dublin with a wealth of habitats and biodiversity. It was designated by UNESCO as a Biosphere Site in 1981 for its recognition of its conservation importance for the presence of several rare and threatened habitats and species listed in Annex I and II of the EU Habitats Directive. The Biosphere was expanded in 2015 and now covers Dublin Bay, reflecting its significant environmental, economic, cultural and tourism importance, and extends to over 300 km2.

Bull island provides an important haul-out site for grey and harbour seals. Such sites are used during breeding, moulting, resting between foraging trips in the open sea, and to engage in social activity. The waters surrounding haul-out sites are a critical habitat for feeding and/or for navigation to more offshore foraging areas. Seals often haul-out on man-made structures and tolerate considerable human activity, which may lead to chronic exposure to man-made noise. In areas with repeated exposure, mammals may become habituated with a decline in avoidance responses and thus become less sensitive to noise and disturbance.


Irish Whale and Dolphin Group Consulting have been carrying out monthly monitoring since May 2016, of the grey and harbour seals which haul-out at North Bull Island, as part of the Alexandra Basin Redevelopment (ABR) Project in Dublin Port. These monthly surveys will be carried out during and after construction for a minimum of two years in line with international best practice.

The haul-out site is surveyed for two hours either side of low water and species, maturity level, behaviour and vigilance are recorded. Long term usage of this site provides a valuable index of seal populations and any disturbance or displacement from the area. Theses surveys are important to build a better understanding of how seals use this site and to ensure there is no effect of the ABR Project.

Up to 20-30 individual seals of both species have been regularly recorded off the north-eastern tip of the island which is approximately 6km to the northeast of Dublin Port. This site is considered far enough away from the construction activity of the ABR Project to prevent any negative effect, especially as sensitivity of seals to disturbance is less when hauled out. Seals generally haul out on sandbanks at North Bull Island near the deep water in Sutton Creek. If they are disturbed by pedestrians or dogs, they may move to an intertidal sandbank opposite Sutton Dinghy Club.


Harbour seals have a year-round presence at the site with grey seals having a seasonal presence arriving at Bull Island late April/early May and leaving late October/early November to breed/moult where they seek more remote undisturbed sites.