Potential of Donegal Bay as an SAC for Bottlenose Dolphins

2nd Feb 2009 Under the EU Habitats Directive, Member States are required to provide strict protection to all species of cetacean (all on Annex IV) within the Irish EEZ. For species on Annex II, Member States are also required to designate Special Areas of Conservation (SAC). This includes the harbour porpoise and bottlenose dolphin. To date, two sites (Blasket Islands cSAC and Roaringwater Bay cSAC) have been designated for harbour porpoise and one site (Lower River Shannon cSAC) for bottlenose dolphin. The National Parks and Wildlife Service (NPWS) are currently seeking information on a number of other sites to assess their potential to be designated as SACs.

A total of 147 sightings of bottlenose dolphins in Donegal Bay were collected by the IWDG between 1994 and 2008. Most sightings were in McSwynes Bay or on the south side of St Johns Point. Sightings have been received regularly by the IWDG since 1994, but the number received each year has increased since 2001. Sightings were received in every month but with a peak from June to October.

Eight dedicated boat-based surveys were carried out in Donegal Bay between July and September 2008. A total of 637km were surveyed. Over 90% of the entire survey time was carried out in sea-state ≤2. Bottlenose dolphins were recorded during three visits to this site. A total of five groups were recorded. All sightings were in the inner bay and none to the west of St Johns Point despite a large amount of survey effort.

Images of bottlenose dolphins were obtained on three occasions with a total of 44 individually recognized. Two individual dolphins were seen on all three trips with dolphins, seven dolphins (15%) were seen on two occasions with the remaining 35 seen on only one occasion. When all individually recognizable dolphins are taken into account then images of both left and right fins were obtained from a total of 20 dolphins, left side of the dorsal fin only for 14 and right side only for 10 dolphins. There were not enough data to derive an abundance estimate using mark-recapture analysis. Two dolphins identified on 23 July 2008 were matched to a group photographed in Galway Bay on 26 March 2007, a distance of 300km and a gap of 483 days. There was also very strong evidence to link one of these dolphins to the Moray Firth, northeast Scotland, however this potential match has not yet been confirmed.

Encounter rates with groups of bottlenose dolphins were lower in Donegal Bay compared to the Lower River Shannon cSAC, however mean group size was much greater giving a similar dolphin encounter rate. Smaller group sizes are typical of resident populations, which are described as having a fission-fusion social structure with individuals leaving and joining different groups regularly. The larger group size in Donegal Bay may reflect the different use of the bay by transient bottlenose dolphins, which enter the bay for short periods before ranging further afield.

Donegal Bay is considered a good candidate for designation as an SAC for bottlenose dolphins, as dolphins regularly use the site in good numbers and there was evidence of site fidelity. We recommend further work is carried out to determine how bottlenose dolphins use the bay, especially regarding the regular presence of the same individuals. This should involve the collection of more photo-identification data to enable a better understanding of their

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