Characteristics of feeding trips of female northern fur seals

Abstract

Female northern fur seals (Callorhinus ursinus) from St. Paul Island, Alaska, were equipped with head-mounted radio transmitters and located at sea to determine their movements and feeding locations during July and August. In 1984, we followed 4 fur seals and located 7 others by ship; in 1985 we located 20 by airplane. Fur seals returned to the rookery during all hours of the day and showed no tendency to arrive during any specific hour; departure was principally from late afternoon to early morning but occurred anytime. Feeding trips averaged 5.9 days and increased in duration from 3.5 days for the first trip to over 7 days for later trips; the mean duration for feeding trips was significantly shorter than those observed in the 1960s and 1970s. During both years radio-tagged fur seals were found northwest and south-southwest of St. Paul Island and some had feeding trips resulting in round-trip distances of about 400 km; one had a round trip of about 740 km. During transit the seals swam in generally direct lines to the feeding areas and one seal followed approximately the same course to and from the feeding area; while there, movement patterns were irregular. Mean swimming speed to the feeding area was 6.5 km/h, and 8.3 km/h on return.