Foraging behaviour indicates marginal marine habitat for New Zealand sea lions: remnant versus recolonising populations

• Published in: Marine Ecology Progress Series
• Main Authors: Augé, A.A., Chilvers, B.L., Moore, A.B., Davis, L.S.
• Format: Article in Journal/Newspaper
• Language: unknown
• Published: Inter-Research 2011
• Subjects: Campbell Island; New Zealand; Auckland Islands
• Online Access: https://researchonline.jcu.edu.au/24084/3/24084_Auge_et_al_2011_Accepted_Version.pdf; https://researchonline.jcu.edu.au/24084/4/24084_Auge_et_al_2011.pdf

The New Zealand sea lion Phocarctos hookeri historically bred on the New Zealand mainland (South and North Islands). Subsistence hunting and later commercial sealing reduced its distribution to 3 breeding areas at the spatial edges of its historical distribution range, in the Auckland Islands (AI) and on Campbell Island. Here, we present foraging areas and foraging trips of female New Zealand sea lions from the Otago Peninsula, where a recolonising population has been found in the core of the historical range of the species. We compare the results with data from the AI in order to assess the theory that the spatial margin of a species' distribution represents the lower end of habitat suitability. Female New Zealand sea lions at Otago had significantly smaller foraging ranges than females at the AI (mean 65% Kernel ranges: 47 ± 25 km2 versus 687 ± 109 km2), made shorter foraging trips (mean 11.8 ± 2.3 h versus 66.2 ± 4.2 h), and spent 40% less time at sea overall. Juvenile females at Otago from age 2 onwards could access foraging grounds used by adult females nursing pups; this is unlikely to be the case at the AI due to the large distances and associated depths of foraging grounds. Our study illustrates the theory that spatial marginality is related to habitat marginality. Existing management measures to mitigate the impact of bycatch in fisheries on declining remnant colonies around the AI were modelled based on populations exploiting optimal habitat. They should now integrate this new information.