Foraging behaviour indicates marginal marine habitat for New Zealand sea lions: remnant versus recolonising populations
Marine Ecology Progress Series
The New Zealand (NZ) sea lion, Phocarctos hookeri, historically bred on the NZ mainland (South and North Islands). Subsistence hunting and later commercial sealing reduced its distribution to three 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 NZ sea lions from the Otago Peninsula, the initial recolonising population found in the core of the historical
... f the historical range of the species. We compare the results with data from the AI in order to assess the theory that populations situated at the spatial margin of a species' distribution represent the lower end of habitat suitability. Female NZ sea lions at Otago had significantly smaller foraging ranges (mean 65% Kernel ranges: 47 ± 25 km 2 versus 687 ± 109 km 2 ), shorter foraging trips (means: 11.8 ± 2.3 h versus 66.2 ± 4.2 h), and spent 40% less time at sea overall than females at the AI. Otago juvenile female NZ sea lions from age two 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.