Summer foraging by lactating female New Zealand fur seals (Arctocephalus forsteri) off Otago Peninsula, New Zealand

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Abstract
The behaviour of female New Zealand fur seals (Arctocephalus forsteri) at sea and on land at the rookery of Fuchsia Gully, Otago Peninsula, New Zealand (45 °52′S, 170 °44′E), was examined during the early stages of lactation in the 1993 – 1994 breeding season. The attendance patterns of 19 females were investigated using daily observation at the rookery. Trips to sea to forage ranged from 3.4 h up to 8 days (mean 3.26 ± 1.1 days), and attendance periods at the rookery ranged from 1 to 13 days (mean 3.09 ± 1.63 days). At sea, the behaviour of four females was examined by deploying time–depth recorders. Females showed a nocturnal pattern of diving, 88.8–97.3% of dives being made during the hours of darkness. For all females and each night of foraging, the deepest dives were completed around dawn and dusk. The deepest dive recorded was 163 m and all females dove over 100 m deep on at least one dive. The overall median dive depth was considerably less than this, as around 24:00–03:00, females undertook many shallow dives, and during this time the median dive depth ranged from 5 to 10 m for the four females. Dives occurred in bouts, but bout duration varied significantly with time of day. Bouts were short during the day and longer at night, 55% of night bouts lasting throughout the night. Maximum dive durations ranged from 3.17 to 6.17 min and mean dive durations from 0.67 to 1.18 min for individual females. Dive depth was significantly related to dive duration for all four females. Two of the females also carried satellite transmitters, and at sea location was determined on three separate nights of foraging. Females were found to be foraging up to 78 km from the rookery, but always over the continental shelf (in water shallower than the 200 m depth contour).

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