The University of Adelaide
South Australian Research and Development Institute
Mapping critical Australian sea lion habitat to assess ecological value and risks to population recovery
Populations of the Endangered Australian sea lion have declined by more than 60% in the past 40 years. There is a marked uneven distribution in abundance and trends across the species range, suggesting that risk profiles from threats vary at small spatial scales. Fine scale differences in foraging behaviour and habitat use within and between colonies are thought to underpin these differences. The seafloor habitats critical to sea lions, their vulnerability to human impacts and the role of existing management measures (marine protected areas) in protecting them, however, are poorly understood.
This project will fit Australian sea lions with underwater cameras on to identify and map critical habitats, assess their ecological value and identify risks to populations. The results will improve our understanding of threats to sea lion populations and support future conservation actions to recover the species.
Threats and declines in Australian sea lion populations
Potential threats to the Australian sea lion include bycatch in fisheries, entanglement in marine debris, disease, pollution, and climate change. Although measures to mitigate bycatch impacts in demersal gillnet and lobster fisheries were introduced a decade ago, recent declines in some populations cannot be explained by fishery interactions.
A recent assessment identified 80 breeding sites with an estimated production of just 2739 pups, (82% in SA, and 18% in WA). Half of these sites produced fewer than 15 pups each breeding season. Time-series data available for 30 breeding sites indicates an average population decline of 2.0% a year, with an estimated 64% decline in abundance over three generations (42.3 years).
Monitoring the population status of Australian sea lions is challenging due to their unique, 18 month breeding cycle that is asynchronous across breeding colonies. Previous satellite tracking and time-depth recorders have provided a wealth of data, but the instruments were too large and unreliable to explore the habitat use of populations. This project will trial improved instrumentation at three key sea lion colonies adjacent to state and Commonwealth marine protected areas.
Underwater cameras and GPS tags will be deployed on Australian sea lions to:
- identify key sea lion habitats, assess their ecological value and further understand their unique relationship with, and dependency on seafloor ecosystems;
- provide new information on the movement and habitat use of sea lions to inform species risk assessments, including threats from fisheries interactions; and
- evaluate the extent to which marine protected areas protect key sea lion habitat.
Tagging Australian sea lions to identify core habitat
The tagging will take place at three sea lion colonies adjacent to Commonwealth and state marine reserves off South Australia including Olive and Pearson Islands (Western Eyre Marine Park) and Seal Bay (Southern Kangaroo Island Marine Park).
Sea lions will be sedated (darted intramuscularly) and anaesthetised (gas anaesthesia). Archival GPS tags with integrated time-depth recorders (Wildlife Computers Mk10+), triaxial accelerometer and magnetometer and miniature underwater camera (Zoolog Solutions) will be glued to the dorsal midline. Instrumented seals will be recaptured following a single foraging trip, usually two to five days from initial capture, and the instruments removed.
Time-matched GPS, video, dive and accelerometer/magnetometer data will be used to identify and map fine-scale habitat/prey use and core ecological habitats in and outside marine protected areas. Habitat and prey will be scored and analysed using video-analysis software, with accelerometer data (measuring head movement) helping to identify events. Magnetometer data will be used to dead-reckon sub-surface movement and assess fine-scale habitat use. Habitat analysis will use the same grading system as those from other marine park monitoring projects that use? remotely operated vehicles and towed surveys.
Australian sea lions fitted with GPS tags and underwater cameras provide a unique and cost-effective record of hundreds of kilometres of seabed, revealing new rocky reefs, kelp forests and seagrass meadows. Estimating the time individual sea lion allocate to different habitats provides a unique means to assess their ecological value.
Information for Australian sea lion conservation and recovery
The project findings will provide information for:
- revision of the Recovery Plan for the Australian Sea Lion;
- evaluation of risks to populations from fisheries interactions (bycatch and prey depletion) and other threats; and
- implementation of the Parks Australia South-west network management plan which recognises the Australian sea lion as both a core natural value, and as being directly impacted by pressures (climate change, extraction of living resources, human presence and marine pollution).
Indigenous consultation and partnership
This project will harness the unique and culturally inclusive approach of connecting people to Sea Country through a culturally significant species, Bul:gada, the Australian sea lion.
In developing this project, the project team consulted with the Far-West-Coast Aboriginal Corporation (FWCAC) and discussed opportunities to connect people to Sea Country. FWCAC is the Native Title prescribed body corporate for six distinct Aboriginal cultural groups, including Wirangu and Mirning. Australian sea lions (Bul:gada) are an important spiritual totem species for the Wirangu peoples. The project will explore opportunities for two-way learning and collaborative fieldwork in partnership with local Aboriginal Rangers.
Australian sea lion breeding sites off South Australia including Olive Island, Pearson Island and Seal Bay, Kangaroo Island.