Technical report

File type: PDF

Groom R, Carter A, Collier C, Firby L, Evans S, Barrett S, Hoffmann L, van de Wetering C, Shepherd L, Evans S, Anderson S (2023). Mapping Critical Habitat in Yanyuwa Sea Country. Report to the National Environmental Science Program. Charles Darwin University.



Yanyuwa country is in the south-west Gulf of Carpentaria (GoC), an area of land and sea that includes the Sir Edward Pellew Islands in the Northern Territory (NT). This intertidal habitat survey was conducted at the request of Yanyuwa Traditional Owners and the li- Anthawirriyarra Sea Ranger Unit to support their sea country planning and management aspirations. This survey forms part of a larger collaborative project that documents marine benthic habitats in Yanyuwa country.

A total of 16,128 + 679 ha of seagrass was mapped in Yanyuwa sea country across 180 individual meadows. This included a series of meadows that stretched ~130 km along the mainland coast. In most instances, meadows extended from the coastal mangroves to the offshore edge of the intertidal zone. The intertidal bank ranged in width from several hundred meters to several kilometres along the mainland coast. Seven seagrass species were recorded on survey with the dominant species being Halodule uninervis, a pioneer species that is a preferred food for dugong and turtle.

All five algae functional groups were recorded, with many sites featuring a mix of groups. Algae was present at 33% of the survey sites and accounted for up to 100% of benthic cover at an individual site. Erect macrophyte algae was the most common algal type and was found throughout the survey area. Hard corals were common along the exposed northern coastlines at Mathandurla, Watson Island, Barranyi (North Island), Limiyamila, and along the northern and eastern coast of Vanderlin Island. Soft corals were less common and recorded along the northern coast lines of Mathandurla, Limiyamila and Watson Island. Sponges were present throughout the survey area, including along the mainland coast. Oysters and barnacles were common around the islands, particularly the rocky coastlines of western Vanderlin Island, southern Barranyi (North Island), and around Mathandurla, WanarrWanarr and Barranyi (Centre Island).

Seagrasses and benthic habitats support highly productive and diverse ecosystems. They are vitally important because they store blue carbon, are a source of food and shelter for marine organisms, oxygenate water, trap sand, recycle nutrients, and provide breeding habitats and nursery areas for many marine organisms. The seagrass habitat reported on here is within the intertidal zone, an area largely owned by Yanyuwa people.

Yanyuwa people are seeking opportunities for greater protection of Yanyuwa country that respect their cultural practice, support intergenerational knowledge transfer and are sustainable. Understanding the distribution of values important to Yanyuwa people is fundamental for decision-making and delineating areas for greater protection. Considering Yanyuwa people’s aspirations for greater protection, we recommend the following in consultation with Yanyuwa people: synthesise and spatially analyse relevant eco-cultural and biodiversity data for Yanyuwa country to identify areas of significance; and work with Yanyuwa people to establish rules for greater protection over these areas to reflect their values in a robust manner. Yanyuwa people should then be supported in discussions with government to mobilise their protection aspirations for greatest impact through regulatory management tools.