Abstract
The New Zealand sea lion, Phocarctos hookeri, is endemic to New Zealand and has only three breeding colonies, all situated in the sub-Antarctic islands. This reduced breeding distribution is the result of human extirpation from most of its pristine range, which included the New Zealand mainland. In 1993, a female bred for the first time on mainland New Zealand, indicating the possible start of the recolonisation. The recolonisation of an urbanised coastline will create interactions between humans, infrastructures and sea lions. No study had however looked at how the New Zealand sea lion uses its terrestrial environment. This study thus aimed to characterise, in space and time, the terrestrial spatial ecology of the female New Zealand sea lions at a breeding colony.
Intensive fieldwork at the Sandy Bay breeding colony, Enderby Island, in the Auckland Islands, during two breeding seasons (between December 2001 and March 2003), produced a large dataset of daily Global Positioning System (GPS) locations of branded females onshore (4252 locations) within the study area (0.7 km²). A habitat type map and a Digital Terrain Model (DTM) of the study area were produced.
The analyses were conducted in ArcGIS at three scales: individual, population and habitat. A two-phase pattern, including a harem phase (aggregation of females, area used < 0.003 km²) and a dispersion phase (spread of females, area used > 0.550 km²), was revealed and characterised using Nearest Neighbour Indices. A dispersion model of an average female was produced based on cumulative Minimum Convex Polygons (MCP) and pup mortality was found to be affected by females’ movements on pupping day. The female population was found to move and shift areas used throughout the dispersion phase while the gregariousness of females was considerably modified between the harem phase and the end of the dispersion phase (80 versus 0.3 females per 100 m²). Temporal analyses of habitat use demonstrated a radical change in habitat preferences between the two phases and a gradual change during the dispersion phase. At the end of the season, females preferred sites in forest and at more than 1.1 km from shore. Male aggressiveness and disturbance, habitat properties and parasite infections are thought to be some of the main factors that drive the terrestrial ecology of the females P. hookeri.
In conclusion, the presence and spatial extent of a female population at Sandy Bay, unusual for a pinniped species, was found to be predictable and thought to be species- specific rather than location-specific. The results of this study can thus be used as a basis for the management of the recolonisation. Human infrastructure and disturbance are likely to interfere with the establishment of new breeding colonies and the ecology of female New Zealand sea lions on mainland New Zealand. Some recommendations based on these results are immediate public awareness and education programs, the monitoring of the new population using a GIS database and the identification, protection against human disturbance and rehabilitation of suitable sites for the establishment of a new breeding colony on the mainland.