Summer diving behaviour of lactating New Zealand sea lions, Phocarctos hookeri

• Published in: Canadian Journal of Zoology
• Main Authors: Gales, N. J., Mattlin, R. H.
• Format: Article in Journal/Newspaper
• Language: English
• Published: Canadian Science Publishing 1997
• Subjects: Auckland Islands
• Online Access: http://dx.doi.org/10.1139/z97-796; http://www.nrcresearchpress.com/doi/pdf/10.1139/z97-796

The diving behaviour of 14 female New Zealand sea lions (Phocarctos hookeri) was recorded during early lactation in January and February 1995 on the Auckland Islands, New Zealand. During 73 trips to sea, 19 720 dives were recorded. The average duration of a foraging cycle was 2.9 days (range 1.4–4.8 days), of which 1.7 days (57%) (range 1.1–3.4 days) were spent at sea and 1.2 days (43%) (range 0.8–2.3 days) ashore. At sea the sea lions dived almost continuously at a rate of 7.5 dives/h and spent a mean of 45% of the time submerged (≥ 2 m). Dive behaviour varied among individuals but showed no diel pattern overall. The dive depth for all dives ≥ 6 m was 123 ± 87 m (mean ± SD) (median 124 m, maximum 474 m) and ranged among individuals from 79 ± 85 to 187 ± 166 m. About half of the dives were in the 101- to 180-m range. The duration of all dives was 3.9 ± 1.8 min (median 4.33 min, maximum 11.3 min); about half (51%) of the dive durations were between 4 and 6 min. Surface interval was 4.5 ± 15.8 min (median 1.9 min). Almost half (44%) of all dives exceeded the calculated aerobic dive limit of each sea lion (range 16–73% for individuals). Most dive profiles were flat bottomed and, we believe, are to the benthos. A mean of 51.5% of all dive time was spent in the deepest 85% of the dive. Prey remains found during this study were primarily of benthic and demersal organisms. Phocarctos hookeri is the deepest and longest diving of any of the otariids recorded to date. We suggest that the dive behaviour may reflect either successful physiological adaptation to exploiting benthic prey and (or) a marginal foraging environment in which diving behaviour is close to physiological limits.