By Erica Mather 02/07/2016

A recent study identifies promising new breeding sites on the Otago Peninsula and the Catlins coast for New Zealand sea lions. Researchers have prioritised the identification and protection of potential breeding habitats for recolonisation along the South Island coast.

The subantarctic islands are home to the only three breeding colonies of the New Zealand sea lion (Phocarctos hookeri, formerly known as Hooker’s sea lion). There has been evidence since 1993 for recolonisation of mainland New Zealand, although the coastline of which the sea lions have returned provides unevenly distributed potential habitats for this threatened endemic species due to coastal urbanisation and development.

Researchers from the University of Otago and Department of Conservation recognised that recolonisation was occurring in selective parts of the South Island mainland. They questioned what made some locations more preferable than others and set out to investigate.

Author, Dr Tony Moore describes how environmental and anthropogenic factors known to affect the presence of sea lions could be used to identify areas suitable for breeding. A geographic information system (GIS) analysis involving multiple criteria was implemented to pinpoint suitable habitats along a 1600km length of the South Island coast.

“Based on environmental and anthropogenic geographic knowledge… we wanted to identify, through spatial analysis and GIS, whether the current breeding locations were identified and more importantly, whether new locations with similar properties were identified.”

The research team has identified promising new breeding sites on the Otago Peninsula and the Catlins Coast. Some of the sites detected by the analysis are areas currently favoured by recolonising sea lions, while other sites provide new locations for sea lions to breed. The findings are published in Ocean & Coastal Management.

Screen shot 2016-07-01 at 12.28.07 PM
Breeding colonies (Auckland and Campbell Islands) and recolonisation sites (Catlins and Otago Peninsula) of the New Zealand sea lion. Historical range includes North, South and Stewart Islands. The study area is the SE coastline between the two black lines on the South and East coasts of the South Island.

Dr Moore emphasises the importance of maintaining the optimal environmental setting that favours sea lion breeding such as the proximity to the beach, coastal forest and estuarine habitat. Strategies to mitigate the anthropogenic effect on breeding areas include controlling visitor access and limiting urban and transport development.

“Coastal areas have long been targets for urbanisation and transport; today most major New Zealand urban settlements and many roads (including highways) are located close to the shoreline. This anthropogenic modification of the coast means that the potential mainland breeding habitats that sea lions are returning to is extremely reduced in area and unequally distributed.”

Although the authors were faced with limited data availability in this study, they recognise the importance of overcoming this problem for the determination of potential habitats for sea lions in a New Zealand-wide analysis. In doing so, the few remaining breeding sites for New Zealand sea lions could be protected and restored.

“The New Zealand sea lion is a threatened species and the facilitation of mainland breeding colonies is a significant step to its long term survival. If this was not to happen, then their distribution would be limited to only three breeding colonies in the subantarctic islands, making them far more endangered.”

The authors note that this new method of habitat identification could be applied to other recolonising species, encouraging better management of their most suitable habitats.

Featured image: One of the breeding colonies on the Auckland Islands, which illustrates what the authors would would like to happen on the mainland. Amélie Augé.

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