The seasonal movements and foraging ecology of female New Zealand fur seals, Arctocephalus forsteri, (Lesson, 1828) from Cape Foulwind, Westland, New Zealand

Abstract

Fifteen adult, presumed breeding, female New Zealand fur seals (Arctocephalus forsten) were caught and radio tagged at Cape Foulwind, near Westport on the west coast of the South Island, New Zealand. The Cape Foulwind colony was chosen because the nearby mountains provided sites for radio-tracking stations and for its proximity to the hoki (Macruronus novaezealandiae) fishery where each year several hundred seals are taken as bycatch. Breeding female fur seals taken as bycatch are likely to breed at Cape Foulwind, the closest large colony to the fishing grounds. The aim of the study was to document the frequency and duration of foraging trips and the distance travelled on those trips. Only females were tagged as they must return to suckle their pups on the colony and were therefore more likely to remain within radio-tracking range. Also as a polygynous species that suckles pups all winter the loss of females can lead to population decline.

The seals were tagged with 2 stage VHF transmitters with a range of at least 100km and a life of up to 10 months. Seals were followed during four tracking periods: April (following moulting), July (the hoki season), November (pre-pupping), and January (post-pupping). In April most seals travelled south of the colony. The furthest that seals were recorded from the Cape Foulwind colony was 62km west, 49km south-west and 21km northwest. Fewer positions were determined in July with locations up to 79km from the colony. Although fewer triangulated bearings were determined in July signals were received from most transmitters possibly indicating a shift in foraging area. Few positions were determined in November and none in January possibly due to transmitter loss and damage. Seals tended to travel further and faster during the day than at night.

Environmental factors such as water depth, wind direction and freshwater inflow were not found to have any obvious effect on where seals went. Fishing boat locations and activity may have had an influence on seal positions in July but not in April or November.