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.

格罗特埃兰岛（Groote Eylandt）东南角的海滩，是卡奔塔利亚湾绿海龟（Chelonia mydas）种群的重要筑巢场所。
绿海龟对于格罗特埃兰岛的原住民传统所有者——阿尼迪利克瓦族（Anindilyakwa）而言，具有重要的文化意义，该区域周边已设立原住民保护区（Indigenous Protected Area, IPA）。绿海龟的传统利用方式包括龟卵采集以及在陆地与近海开展捕猎活动。此前，在每年10月至11月期间，达伦巴湾（Dalbumba bay）附近的Amjakikba海滩及其邻近海滩，曾记录到大量绿海龟爬行轨迹。
近年来，负责该区域文化事务的Mamarika氏族担忧本区域绿海龟种群的健康状况，认为当前的捕捞方式已不可持续。作为由阿尼迪利克瓦土地与海洋护林员团队（Anindilyakwa Land and Sea Rangers, ALC Rangers）、Mamarika传统所有者、澳大利亚海洋科学研究所（Australian Institute of Marine Science, AIMS）与查尔斯达尔文大学（Charles Darwin University, CDU）牵头的合作项目的一部分，研究团队于2021年10月开展了为期10天的海龟营地活动，以收集达伦巴湾区域筑巢绿海龟的筑巢频率及筑巢后移动模式相关数据。本次海龟营地共有9名护林员、3名ALC其他工作人员、15名传统所有者，以及3名AIMS/CDU研究人员参与。
在为期10天的营地活动中，团队对Amjakikba海滩及周边3处邻近海滩开展了筑巢海滩调查。调查内容涵盖上岸尝试筑巢的海龟数量，以及实际完成筑巢的巢数。研究人员还为10只上岸筑巢的健康绿海龟佩戴了卫星追踪器，以收集筑巢季内达伦巴湾周边的活动数据，记录筑巢季结束后海龟的迁徙路径，并确定其觅食地。活动期间，研究人员向护林员与传统所有者传授了海滩调查、卫星标记技术，以及收集筑巢基线数据的方法。本次营地同时为护林员提供了学习绿海龟生态学知识的契机，助力其提升能力，以开展长期海龟监测项目，并向社区宣传可持续的海龟利用方式。
10天的海滩调查共在Amjakikba海滩及3处邻近海滩记录到754条海龟爬行轨迹，其中140条被确认为筑巢巢迹（仅1巢非绿海龟巢），筑巢成功率为18.5%，相对偏低。Amjakikba海滩的筑巢密度为38.8巢/千米，活动期间每晚平均成功筑巢数为4.82（±1.03 标准误）。除1只外，所有佩戴卫星追踪器的海龟均留在卡奔塔利亚湾内，它们在达伦巴湾周边停留11至78天后，会迁徙至觅食地。这些觅食地位于卡奔塔利亚湾南部，涵盖利门湾（Limmen Bight）、爱德华·佩卢爵士群岛（Sir Edward Pellew Islands）与韦尔斯利群岛（Wellesley Islands）。10只标记海龟中仅有1只未前往卡奔塔利亚湾南部，而是绕经卡奔塔利亚湾西侧迁徙2236千米，抵达达尔文附近的觅食地。
活动期间，团队还与ALC媒体合作制作了一部纪录片，内容涵盖绿海龟的生物学特性、其与阿尼迪利克瓦族文化的关联，以及可持续捕捞实践对维持格罗特埃兰岛健康绿海龟种群的重要性。基于本研究的发现，我们向护林员和传统所有者提出了若干管理筑巢海滩、保障绿海龟种群健康的建议，包括对筑巢海滩实施季节性封闭、限制成年雌海龟及龟卵的捕捞、收集更多关于幼龟孵化成功率的数据，以及建立持续的海滩监测项目。海龟的筑巢后移动模式凸显了对绿海龟实施区域化管理的必要性，即阿尼迪利克瓦、马拉（Marra）、扬尤瓦（Yanyuwa）、恩布尔瓦尔（Numbulwar）以及阿纳姆海东南区域的传统所有者群体应成为决策核心，并与政府机构开展联合管理。