Influence of time of day and month on Weddell seal haul-out patterns at the Vestfold Hills, Antarctica

A diurnal pattern in haul-out behaviour has been described for Weddell seals at McMurdo Sound, Antarctica, but regional and seasonal variations were previously unknown. Knowledge of activity patterns is important for standardising census methods and census data. This study quantified the diurnal pattern in haulout behaviour of Weddell seals at the Vestfold Hills from October 1994 to March 1995. Sequential counts of seals on the ice showed that, between 0900 and 1930 hours, seal abundance differed up to 95%. Fewer seals were hauled out in the morning than in the afternoon. The maximum numbers of seals were hauled out at the warmest time of day. The diurnal cycle was less pronounced in the breeding season than in the moulting season. The findings indicated the importance of censusing Weddell seals after 1430 hours and before 1700 hours local time, especially in the moulting season. Correction factors are given for month and time of day.