DISTRIBUTION AND ABUNDANCE OF BOTTLE-NOSED DOLPHINS TURSIOPS-TRUNCATUS (MONTAGU) IN THE SHANNON ESTUARY

The feasibility of developing commercial whale-watching in the Shannon Estuary was investigated by determining the distribution and abundanc e of bottle-nosed dolphins in the estuary. A variety of field techniqu es were employed, including photo-identification, fixed boat transects , scan sampling, minimum number estimates and the collection of incide ntal sightings over an eighteen-month period. Land-based observations showed that the presence of dolphins was influenced by the state of th e tide, with a peak in sightings recorded three hours after high water . Dolphins were observed on 25 (61%) of 41 boat transects surveyed, of which sixteen turned into encounters, with dolphins sometimes present for many hours. A minimum number estimate conducted on 16 October 199 4 showed that at least 56-68 animals were present, and photo-identific ation has recognised 25 animals individually. Dolphins were often reco rded in discrete areas, especially off Kilcredaun Head, Beal Bar and o ff Leck Point. Sighting records from the Tarbert to Killimer ferry sho wed that dolphins were regularly seen especially in the spring and sum mer (May to August), being recorded on up to 88% of days in the month. Photo-identification showed that the same dolphins were present in th e estuary throughout the study period, suggesting that they were resid ent. This is the first known resident population of bottle-nosed dolph ins in Ireland. The implications of this work for the development of c ommercial dolphin-watching in the estuary are discussed.