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 collated existing information on key aggregation sites and ‘new’ sites where GNS gather in eastern and western Australia. It also investigated 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 and findings

Compiling an evidence base

The project team compiled and summarised existing knowledge for Australia’s listed grey nurse shark aggregation sites and available data on acoustically-tagged grey nurse sharks detected at key NSW aggregation sites. Additional field research explored grey nurse shark presence and behaviour at potential (as yet unlisted) aggregation sites in Commonwealth waters off Queensland and New South Wales.

In Queensland, acoustic receiver coverage was extended at Barwon Banks off Mooloolaba. In New South Wales, underwater camera systems were used to record the presence of grey nurse sharks at the Outer Gibber Reef in the Hunter Marine Park.

The fieldwork program found several east coast aggregation locations that are not afforded the same levels of protection as the existing listed key aggregation sites. An interesting finding was the confirmation of anecdotal information that grey nurse sharks occur at Outer Gibber Reef in the Hunter Marine Park. 

In Victoria, surveys of potential grey nurse habitat off the coast of west Gippsland were undertaken using underwater camera systems and sampling for environmental DNA (eDNA). No grey nurse sharks were detected. The Victorian component of the project also supported training opportunities in the use of survey tools for Indigenous rangers. This included ranger groups from the Gunaikurnai Lands and Water Aboriginal Corporation, Eastern Maar Aboriginal Corporation, and the Bunurong Land Council Aboriginal Corporation.

Changing definitions

The field work and information synthesis identified commonalities and assisted with developing a structured pathway to defining what constitutes a grey nurse shark aggregation site.

The new proposed definition is that a grey nurse aggregation site is a discrete area where two or more grey nurse sharks can be observed on a predictable basis (such as annually or seasonally) and that includes one or more behavioural drivers consistent with the BIA and ISRA frameworks. Where two or more grey nurse sharks occur at a site on a predictable basis, be it for feeding, breeding or resting, this would be the new criteria for calling it an aggregation site.

As the population continues to increase, it is envisaged that grey nurse sharks will aggregate at more locations. This is currently being seen at NSW sites such as Jervis Bay, Port Stephens and Bushrangers Bay.

Outcomes

Information provided by this project demonstrates what makes an aggregation for grey nurse shark and how the criteria can be applied for future assessments.

Commonwealth and state management agencies now 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