Individual identification, population dynamics and moult of the New Zealand sea lion at Otago.
|Institution:||University of Otago|
|Full text PDF:||http://hdl.handle.net/10523/5209|
A photographic record was kept of all New Zealand sea lions seen at seven study sites in Otago, New Zealand, throughout 1995. Seventy-nine sea lions were individually identified using distinctive features on the flippers, face and body such as rips, nicks and surface scars and estimates of age class. The most commonly used features were those found on the periphery of both the fore and hind flippers. Over 90% of individual sea lions seen were identifiable. The computer program written in this study to improve the speed and accuracy of identifying sea lions was found to vary in effectiveness depending on the experience of the researcher. Using the program experienced researchers correctly matched animals more rapidly and more frequently than inexperienced researchers. Approximately 75% of animals identified at Otago Peninsula were present for at least six months of 1995. All individuals identified in 1994 were also seen in 1995, indicating a majority of resident animals. Numbers of sea lions ashore reached a maximum during spring and autumn and a minimum during winter and summer. Low numbers during summer were related to an absence of older animals. Low numbers during winter appeared to be due to a change in haul-out behaviour. Diurnal activity was investigated via the presence and absence of one-year old male sea lions at Roaring Bay, South Otago. Arrivals and departures peaked at mid-morning and mid-afternoon, behavioural activity peaked at 1400h, and the animals showed virtually no nocturnal activity. Only three females were present at Otago Peninsula during the study period: a breeding female and her two offspring, the first pups to be born on the mainland of New Zealand in recorded history. The timing and pattern of moult was recorded for male sea lions. Younger males moulted first with two-year olds beginning in December- January. Generally moult occurred later for each successive age class. Animals older than four began moulting in March- April. The exception was the one-year old age class, which moulted at a similar time to animals five years and older, but only went through a partial moult.