Project Title: A spatially explicit population model to inform negotiations between Traditional Owners and the relevant management agencies about options to manage the dugong fishery in Torres Strait
Chief Investigators: Prof Helene Marsh and Ms Alana Grech
The dugong is of the highest cultural value to the Indigenous peoples of Torres Starit where the globally significant dugong population supports a culturally important Indigenous fishery. The fishery is protected by the Torres Strait Treaty between Australia and Papua New Guinea which obliges the signatories to miminmise any restrictive effects on the traditional activities of traditional inhabitants.
Aerial surveys for dugongs conducted since the mid 1980s using standardised methodology have provided long-term information on the distribution and abundance of dugongs in the Torres Strait region. We used information collected from six dugong aerial surveys spanning 19 years in conjunction with geostatistical techniques, including universal kriging, to develop a spatial model of dugong distribution and relative density in the Torres Strait. We categorised areas as of low, medium or high ecological value for dugongs in Torres Strait based upon the relative densities integrated across surveys. Our approach assumes that dugong density is a robust index of a regions value for dugongs. The model accounts for temporal changes in the use of various regions by dugongs including movements resulting from events such as seagrass dieback by integration information across surveys.
The resultant spatial model allowed us to quantify the importance of Torres Strait as dugong habitat in the context of the entire east coast of Queensland (south-east Queensland, Great Barrier Reef Region and Torres Strait) using the same technique. The model indicates that 74 % of the total high value dugong habitats and 63 % of the total medium value habitats on the eastern coast of Queensland are in Torres Strait. In addition, a larger proportion of the Torres Strait survey region (36%) is of high value for dugongs than the inshore waters of the Great Barrier Reef region (3%) or the large bays of southeast Queensland (20%).
With co-funding from the Marine and Tropical Research Facility, this information on dugong distribution and relative density is being shared with Torres Strait Islanders via a series of community mapping workshops held at Mabuiag, Boigu, Badu, Yam, Hammond, and Horn Islands. At the workshops, participants are being taught how to use the overlay functions of geographical information systems (GIS) to combine their traditional ecological knowledge, dugong aerial survey information and the model of dugong distribution and relative density. Digital and hard copy format copies of the model have also been provided to the Torres Strait Regional Authority to inform their regional resource management initiatives.
The spatially explicit dugong population model will inform negotiations about shared responsibility strategies for ensuring that the Torres Strait dugong fishery is sustainable. The draft Torres Strait Dugong and Turtle Fishery Strategic Assessment Report commissioned by the Australian government recommends that a study be undertaken in association with Islander communities to identify/evaluate alternative mechanisms available at the community level to limit and monitor catch. This model contributes to the fulfilment of this recommendation by providing Islanders and management agencies with scientifically robust information on the spatial distribution of dugongs in Torres Strait, as the part of the science base for assessing management options such as spatial closures to hunting or limiting the hunting of each community to their own sea country.