Foraging range and at-sea locations of female Antarctic fur seals, Cape Shirreff, Livingston Island, from 1999–2002

During the breeding season, Antarctic fur seals are central-place foragers, ranging from their colony to feeding areas hours to days offshore, returning periodically to suckle. Outside of this, little is known about a female’s foraging strategy, her success upon which depends not only her survival but that of her young. As such, a fundamental component to understanding the survival and reproductive success of fur seals is to identify habitat preferences. Our objective was to characterize the distribution and range of foraging females rearing pups at Cape Shirreff, Livingston Island, Antarctica. We instrumented 95 females with ARGOS satellite-linked transmitters prior to departures on foraging trips from late December to late February for four consecutive breeding seasons (1998/99-2001/02). We had 7,550 successful at-sea satellite locations (mean: 12/day/female, SE±0.11), after the data were filtered to eliminate positions that required females to travel >4m/sec. Foraging trip lengths averaged 4.0 days (SE±0.11). The mean range traveled offshore was 83.3km (SE?2.9) and the maximum distance was 369.1km. Foraging trip length was positively correlated with both foraging range (r2=0.48, F1,169=157.73, P<0.001) and the total distance traveled (r2=0.59, F1,169=237.06, P<0.001) indicating that foraging range can be estimated for females without satellite-linked instruments based on their trip duration alone. Trip duration, foraging range, and total distance traveled showed significant decreasing trends over the four years of our study. At-sea foraging locations in all years were centered over the mouth of a canyon at the continental shelf break ca. 40 km northwest of Cape Shirreff. A comparison of Cape Shirreff fur seal foraging locations and the krill fishery in area 48.1 shows that the fishery, from 1999-2001, took 70% of the total 48.1 take within 100km of Cape Shirreff and the foraging range of fur seals.