Using mobile phone telemetry to investigate the haul-out behaviour of harbour seals Phoca vitulina vitulina

Information on the haul-out behaviour of pinnipeds is essential for increasing the accuracy of population estimates necessary for the effective conservation of protected species, as well as improving survey design. The haul-out behaviour of 10 harbour seals Phoca vitulina L. in southwest Ireland was examined using a novel telemetry system based on global systems for mobile communications technology. The data on the haul-out patterns of tagged individuals were examined using generalised additive modelling to determine potential factors of influence, such as the tide, the time of day and the time of year. The behaviour varied among seals, with time ashore reaching a maximum during post-moult in October and decreasing to a minimum in February. A strong tidal influence on haul-out behaviour was evident. Tagged seals hauled out more frequently at low tide. There was variation between individuals in the influence of time of day on haul-out behaviour. A cyclic pattern with lunar periodicity was evident in seals tagged in October, and the pattern varied between tidal periods. There was an overall large variation in patterns of behaviour over the tagging period, both between individuals and between tidal periods for each individual. This cautions against making inferences on the haul-out behaviour of the 'population' based on the behaviour of a small number of tagged individuals. The present study provides detailed information, heretofore unavailable, on the haul-out behaviour of individual harbour seals and on the behaviour of the species in Ireland, and it has important implications for population assessment for conservation purposes across the species' entire geographical range.