Grey nurse shark aggregations

Grey nurse sharks (GNS) are known to aggregate at specific sites along migration routes. For the eastern GNS, there are 19 identified ‘key aggregation sites’ in New South Wales and Queensland. The term key aggregation site was defined in 2003 as a site consistently occupied by five or more GNS. There is a need to formalise this definition and develop criteria to be able to ensure a consistent approach to existing and any potential sites.

This project will collate existing information on key aggregation sites and ‘new’ sites where GNS gather in eastern and western Australia. It will also investigate an area in Victoria where there is evidence GNS are present for at least a part of the year. This information will be made available to refine the definition of key aggregation sites and develop criteria to allow assessment of potential new sites.

Approach

The project team will look at existing patterns of occupancy to help devise a clear and defensible definition of an aggregation site. This will involve:

1. Investigating potential new sites that may meet the definition of an aggregation site and draft a plan for future research needed to help classify these new sites (state and commonwealth waters).
2. Surveying a site in Victorian waters where GNS have been observed and potential suitable habitat at other sites, such as around rocky islands.
3. Expanding acoustic receiver deployments on the Barwon Banks in Queensland to monitor acoustically-tagged GNS.
4. Conducting an initial baited remote underwater video (BRUV) survey of a potential GNS aggregation site off New South Wales in commonwealth waters.
5. Reviewing data on the western population of GNS.

Victorian surveys

The distribution of the eastern GNS has been reported to extend into Victorian waters. However, sightings have been exceptionally rare over the past several decades. Limited recent sightings at Gabo Island and near Corner Inlet may indicate that GNS are re-inhabiting the region. This project will survey a region near Corner Inlet for suitable habitat using a combination of remotely operated underwater vehicle (ROV) and environmental DNA (eDNA). These surveys will be conducted in partnership with the traditional custodians of the region through the Gunaikurnai Land and Waters Aboriginal Corporation (GLaWAC) Sea Country program.  

In addition to the surveys in Gippsland, local community engagement will be key to identifying potential aggregation sites and areas where GNS have been observed. For this engagement, the project team will create communication materials and meet with local dive operators, fishing operators, and freediving clubs to encourage information sharing about GNS observations.

New South Wales surveys

GNS have been reported at a reef system in the Commonwealth Hunter Marine Park. An initial BRUV survey of the reef will be conducted to determine whether the sharks present are GNS. If so, towed video/ROV will be used to survey the region.

Queensland surveys

Barwon Banks, located in commonwealth waters off the Queensland coast, is a possible aggregation site. However, diver surveys of the site are irregular and only a single acoustic receiver has been deployed to detect acoustically tagged GNS. This project will expand acoustic coverage of Barwon Banks with an aim to provide data for future analyses in aid of determining the importance of Barwon Banks to the eastern GNS.

Western Australian surveys

Several potential western GNS aggregation sites have been identified in Western Australian waters. This project will review the available evidence and determine a plan for future investigation.

Expected outcomes

Commonwealth and state management agencies will have:

• a clear and unambiguous definition of what constitutes a GNS aggregation site that will assist in assessing existing and new sites for listing or delisting; and
• a list of potential new GNS aggregation sites to consider for further investigation/categorisation.

Project location