Photo-identification of fin whales (Balaenoptera physalus L.) off the south coast of Ireland

Photo-identification of fin whales (Balaenoptera physalus L.) was carried out off the south coast of Ireland between 2003 and 2008. During 79 research trips, mainly on-board a whale watching vessel, 62 individual fin whales were identified using a variety of marks, including notches in the dorsal fin, blotches and scars. Forty (65%) of these whales were only seen once but eleven whales (18%) have been recorded within a year on up to four occasions within a season and eleven whales (18%) re-sighted between years with one recorded in four and one in five of the last seven years. Re-sighting rate varied depending on the marks used to identify whales but was 17.7% overall. The mean interval between the first and last reported sighting was 33.2 days, with a minimum of one day and a maximum interval of 165 days. The south coast of Ireland is an important site for fin whales and provides excellent research opportunities due to their close proximity to land.