As this is my first blog, I thought I would give a bit more background to the project and to the white sharks of the Neptune Islands.
Research on the movement patterns of white sharks in Australian waters has identified that there are specific sites and areas where the species commonly visit. Acoustic listening stations deployed at the Neptune Islands have shown that some white sharks show residency patterns at these islands, returning annually for periods of up to four months, with records showing some individuals exhibiting this annual residency pattern for 10 years or more. The Neptune Islands have thus been identified as important aggregation grounds for the species and additional protection measures in these zones have been proposed. However, tagging studies have also shown that white sharks travel extensively across their range in Australian waters and visit other areas with regularity. In addition, some areas where white sharks are regularly seen appear not to have been visited by sharks tagged at the Neptune islands. It is therefore likely that there are other key habitats at which individual sharks may exhibit similar residency patterns to those visiting the Neptune Islands, or where individuals frequently revisit, and these areas would be equally sensitive areas for the species.
In South Australia, white sharks have a relatively large home range that encompasses a number of habitats that sharks visit on a semi-regular basis and utilize for feeding. Satellite and acoustic tagging studies have identified common routes associated with the 60-120 depth zone along which some white sharks commonly migrate in various areas of Australia suggesting that this depth zone is an important corridor for movement around Australia’s coast, and so we plan to deploy listening stations in areas along these “cafe highway” routes.
Much research has been conducted on white sharks at the Neptune Islands over the last 10 years, incorporating operators log book data, photographic identification, genetic sampling, fine scale movement studies and acoustic and satellite tagging. However, since this data collection has been limited to the Neptune Islands, there is limited understanding as to how such data relates to the behaviour and habitat use of the overall population. This has ramifications for using sites such as the Neptunes for monitoring trends in population size and status. The North Neptune Island group is one of several significant seal colonies in South Australian waters, and is clearly an important habitat to which some white sharks show high degree of site fidelity. But it is not known if these sharks spend periods of residency at other islands, nor how important other seal colonies are sharks that may not visit the Neptune Islands group. This project aims to identify such key habitats for white sharks in South Australian waters.
We are now eagerly awaiting the delivery of our new acoustic receivers and are looking forward to a deployment expedition in the next couple of months!