In the shallow end: diving behaviour of recolonising female New Zealand sea lions (Phocarctos hookeri) around the Otago Peninsula

摘要

Female New Zealand sea lions (Phocarctos hookeri (Gray, 1844)) at the Auckland Islands (remnant populations) are the deepest and longest diving otariids. These remnant populations are found at the margin of the historical range of the species. We hypothesized that diving behaviours of animals in the core of their historical range is less extreme owing to a better marine habitat. All female New Zealand sea lions (n = 13, aged 2-14 years) born on the Otago Peninsula (initial recolonising population) were equipped with time depth recorders during April and May 2008, 2009, and 2010. The mean dive depth was 20.2 +/- 24.5 m and mean dive duration was 1.8 +/- 1.1 min, some of the lowest values reported for otariids. Otago female New Zealand sea lions did not exhibit two distinct diving specialisations as reported at the Auckland Islands. Otago adult females exceeded calculated aerobic dive limits in 7.1% of dives compared with 68.7% at the Auckland Islands. The contrasting differences in diving behaviour between Otago and the Auckland Islands suggest that Otago represents a better marine habitat for New Zealand sea lions, with food easily accessible to animals of all ages.