Nesting density and movement patterns of Green Turtles on Groote Eylandt

The beaches on the south-eastern corner of Groote Eylandt are significant nesting sites for the Gulf of Carpentaria stock of green turtles (Chelonia mydas). Green turtles are a culturally significant species to the Aboriginal Traditional Owners of Groote Eylandt (Anindilyakwa), with an Indigenous Protected Area (IPA) implemented around the Eylandt. The customary use of green turtle includes egg collection and hunting on land and in water. Previously, high green turtle track counts have been recorded at Amjakikba beach and its adjacent beaches near Dalumba bay, during October and November. In recent years, the Mamarika clan who have cultural responsibility for this area have raised concerns about the health of the green turtle population in this region due to perceived unsustainable harvest practices. As part of a collaborative project led by the Anindilyakwa Land and Sea Rangers (ALC Rangers), Mamarika Traditional Owners (TOs), the Australian Institute of Marine Science (AIMS) and Charles Darwin University (CDU), we conducted a 10-day turtle camp in October 2021 to collect information on the nesting frequency and post-nesting movement patterns of green turtles nesting at in the Dalumba bay region. This turtle camp included participation and contribution of 9 Rangers, 3 other ALC staff, 15 Traditional Owners and 3 AIMS/CDU research staff. During the 10-day camp, the team conducted nesting beach surveys on Amjakikba beach and 3 adjacent beaches. The surveys collected data on the number of turtles that came ashore to attempt nesting, and the number of nests laid. Ten healthy turtles were also tagged with satellite transmitters while ashore nesting to collect information on the area used near Dalumba bay during the nesting season and to document their migration away from the area at the end of the nesting season and identify the foraging areas. During the camp, the Rangers and TOs were trained by the researchers to conduct beach surveys, satellite tagging, and collect baseline information on nesting. The camp was an also an opportunity for the Rangers to develop their understanding of green turtle ecology and build their capacity to develop a long-term turtle monitoring program that engages with the community about sustainable turtle use.The beach surveys recorded 754 tracks across Amjakikba and three adjacent beaches over 10 days, of which 140 were confirmed to be nests (all but one were green turtle nests). This equated to nesting success of 18.5% which is relatively low. Nesting density on Amjakikba beach was 38.8 nests km-1, with an average of 4.82 (± 1.03 SE) successful nests laid per night during the camp. All but one of the satellite tracked turtles stayed within the Gulf of Carpentaria, with turtles spending 11 – 78 days around Dalumba bay before migrating to find foraging grounds. These foraging grounds were in the southern Gulf of Carpentaria and included Limmen Bight, Sir Edward Pellew Islands and Wellesley Islands. Only one of the ten tagged turtles did not travel to the southern Gulf, but rather migrated 2,236 km around the western side of the Gulf of Carpentaria to foraging grounds near Darwin. During the camp, the team worked with ALC Media to develop a documentary on the biology of green turtles, their links with Anindilyakwa culture and the importance of sustainable harvesting practices to ensure a healthy population on Groote Eylandt. Based on the findings of this study we provide some recommendations to Rangers and Traditional Owners to manage the nesting beaches and ensure healthy Green Turtle populations. These recommendations included seasonal closures of nesting beaches, harvest restrictions on adult female turtles and nests, collection of additional data on hatchling success, and the development of ongoing beach monitoring programs. The post-nesting movements of turtles highlighted the need for a regional approach for green turtle management, where Traditional Owner groups from Anindilyakwa, Marra, Yanyuwa, Numbulwar and southeast Arnhem sea countries should be central in decision-making and joint management with government agencies.

Groote Eylandt东南角的海滩是卡奔塔利亚湾绿海龟（Chelonia mydas）种群的重要筑巢地。绿海龟对Groote Eylandt的原住民传统所有者（Anindilyakwa人）而言是具有文化重要性的物种，该岛周边已设立原住民保护区（Indigenous Protected Area, IPA）。绿海龟的传统用途包括卵的采集以及陆地上和水中的捕猎。此前，10月至11月期间，在Amjakikba海滩及其邻近Dalumba湾的周边海滩记录到了较高的绿海龟足迹数量。近年来，对该区域负有文化责任的Mamarika氏族已对绿海龟种群健康表示担忧，原因是他们认为当前的捕猎实践不可持续。

作为Anindilyakwa陆地与海洋护林员（Anindilyakwa Land and Sea Rangers, ALC Rangers）、Mamarika传统所有者、澳大利亚海洋科学研究所（AIMS）和查尔斯达尔文大学（CDU）牵头的合作项目的一部分，我们于2021年10月开展了为期10天的海龟营地活动，以收集Dalumba湾区域绿海龟筑巢频率及筑巢后移动模式的信息。该营地活动有9名护林员、3名其他ALC员工、15名传统所有者和3名AIMS/CDU研究人员参与并贡献力量。在10天的营地期间，团队对Amjakikba海滩及3个邻近海滩进行了筑巢海滩调查，收集了上岸尝试筑巢的海龟数量及已筑巢穴数量的数据。此外，10只健康海龟在岸上筑巢时被安装了卫星发射器（satellite transmitters），以收集它们在筑巢季节期间在Dalumba湾附近活动区域的信息，并记录其筑巢季结束后离开该区域的迁移路径及觅食地位置。研究人员还培训护林员和传统所有者开展海滩调查、卫星标记及收集筑巢基线信息。该营地也是护林员加深对绿海龟生态学理解的机会，并帮助他们建立能力，以制定一个让社区参与可持续海龟利用的长期海龟监测项目。

海滩调查显示，10天内Amjakikba及3个邻近海滩共记录到754条海龟足迹，其中140个被确认为巢穴（除1个外均为绿海龟巢穴），这相当于18.5%的筑巢成功率，相对较低。Amjakikba海滩的筑巢密度为38.8巢/公里，营地期间每晚平均成功筑巢4.82±1.03标准误差（SE）个。除1只外，所有卫星追踪的海龟均留在卡奔塔利亚湾内，它们在Dalumba湾周边停留11至78天后迁移至觅食地。这些觅食地位于卡奔塔利亚湾南部，包括Limmen Bight、爱德华·佩勒韦爵士群岛（Sir Edward Pellew Islands）和韦尔斯利群岛（Wellesley Islands）。10只标记海龟中仅有1只未前往南部海湾，而是沿卡奔塔利亚湾西侧迁移2236公里，到达达尔文附近的觅食地。

营地期间，团队与ALC媒体（ALC Media）合作制作了一部纪录片，内容涉及绿海龟的生物学特性、它们与Anindilyakwa文化的联系，以及可持续捕猎实践对确保Groote Eylandt绿海龟种群健康的重要性。基于本研究的发现，我们向护林员和传统所有者提供了若干建议，以管理筑巢海滩并确保绿海龟种群健康。这些建议包括筑巢海滩的季节性关闭、对成年雌龟和巢穴的捕猎限制、收集更多幼龟孵化成功率的数据，以及制定持续的海滩监测项目。海龟的筑巢后移动模式凸显了绿海龟管理采取区域方法的必要性，其中来自Anindilyakwa、Marra、Yanyuwa、Numbulwar和东南阿纳姆海域国家的传统所有者群体应在决策中处于核心地位，并与政府机构联合管理。