Marine wildlife management in the Northern Great Barrier Reef World Heritage Area - Spatial models of dugong distribution and relative density of aerial surveys from 1990 - 2013 (NERP TE 1.2, JCU)

This dataset shows a raster spatial model of the distribution and relative density of dugongs (Dugong dugong) in the northern Great Barrier Reef region based on an aggregate of 24 years (1990 - 2013) of systematic aerial surveys. Methods: Aerial surveys were conducted using the strip transect method described by Marsh and Sinclair (1989). The survey region was divided into blocks containing systematic transects of varying length, which were typically perpendicular to the coast across the depth gradient. Tandem teams with two observers on each side of the aircraft independently recorded sightings of dugongs, including information on group size and calf numbers. Transects were 200 m wide at the water’s surface on either side of the aircraft. The spatial data from all the aerial surveys in the region (1990, 1995, 2000, 2006, and 2013) were corrected for differences in sampling intensity and area sampled between surveys. For details on sampling intensities and areas, please refer to the reports and publications for each individual survey (list below). The corrected data were then interpolated using universal kriging over the spatial extent of the aerial surveys. Planning units were 2km * 2km and were classified as low (1), medium (2), high (3) and very high (4) dugong density on the basis of the relative density of dugongs estimated from the model and a frequency analysis. Low density areas: 0 dugongs per square km; medium density areas 0.0015 - 0.25 dugongs per square km; high density areas 0.25 - 0.5 dugongs per square km; very high density areas > 0.5 dugongs per square km. Limitations: The modelled abundance and distribution show the relative density of dugongs (areas where there are more or less animals) and NOT the absolute dugong density as corrections for perception bias (animals that are available to, but missed by, observers) and availability bias (animals that are unavailable to observers because of water turbidity) can only be applied at the spatial scale of entire surveys (thousands of square kilometres), making them inappropriate for the spatial scale for this dataset. Nonetheless, the relative densities among regions should be approximately comparable (H. Marsh, personal communication). Format: The spatial model is 2481x3509 pixels with a spatial reference of WGS84 UTM Zone 54S. The original dataset is stored in ESRI GRID format (60 KB), which was converted to a GeoTiff for use in the eAtlas (134 kB). Both datasets are available under a creative commons attribution license. References: Publications for aerial surveys in the northern Great Barrier Reef: Marsh, H. & Corkeron, P. (1996). The status of the dugong in the northern Great Barrier Reef. Report to Great Barrier Reef Marine Park Authority, Townsville. Marsh, H. & Lawler, I. R. (2002). Dugong distribution and abundance in the Northern Great Barrier Reef Marine Park: November 2000. GBRMPA Research Publication 77. Townsville, Australia: Great Barrier Reef Marine Park Authority. Marsh, H.D., Hodgson, A., Lawler, I., Grech, A., & Delean, S. (2007) Condition, status, and trends and projected futures of the dugong in the Northern Great Barrier Reef and Torres Strait; including identification and evaluation of the key threats and evaluation of available management options to improve its status. Marine and Tropical Sciences Research Facility Reports Series. Reef and Rainforest Research Centre Limited, Cairns (77pp.). Data Location: This dataset is filed in the eAtlas enduring data repository at: data\NERP-TE\1.2_GBR-Turtles-dugong-monitoing本数据集基于1990年至2013年共计24年的系统航空调查汇总数据，构建了大堡礁北部区域儒艮（Dugong dugong）的分布与相对密度栅格空间模型。 ## 调查方法 航空调查采用Marsh与Sinclair（1989）提出的带状样带法开展。调查区域被划分为若干区块，每个区块包含不同长度的系统样带，这些样带通常垂直于海岸并跨越深度梯度。飞机两侧各配备两名观察员，组成双人搭档小组，独立记录儒艮的目击信息，包括种群规模与幼崽数量。样带在飞机两侧的水面上方宽度为200米。 本区域1990、1995、2000、2006及2013年所有航空调查获取的空间数据，已针对不同调查间的采样强度与采样面积差异完成校正。如需了解采样强度与采样面积的详细信息，请参阅各项单独调查的报告及出版物（列表如下）。校正后的数据随后通过通用克里金法（universal kriging）在航空调查的空间范围内进行插值。 规划单元尺寸为2km×2km，基于模型估算的儒艮相对密度与频率分析结果，被划分为低（1）、中（2）、高（3）与极高（4）四个密度等级：低密度区域为每平方公里0头儒艮；中密度区域为0.0015~0.25头/平方公里；高密度区域为0.25~0.5头/平方公里；极高密度区域为>0.5头/平方公里。 ## 局限性说明 本模型估算的丰度与分布仅表征儒艮的相对密度（即动物种群数量较多或较少的区域），而非绝对密度。这是因为感知偏差（观察者可观测范围内但被遗漏的动物）与可用性偏差（因水体浑浊而无法被观察者观测到的动物）的校正仅能在整个调查的空间尺度（数千平方公里）上实施，不适用于本数据集的空间尺度。不过，不同区域间的相对密度仍具备大致可比性（H. Marsh，私人通信）。 ## 数据格式 本空间模型分辨率为2481×3509像素，空间参考为WGS84 UTM 54S带（南纬）。原始数据集以ESRI GRID格式存储（大小为60 KB），为便于在eAtlas中使用，已转换为GeoTiff格式（大小为134 KB）。两份数据集均采用知识共享署名许可协议发布。 ## 参考文献 大堡礁北部区域航空调查相关出版物： 1. Marsh, H. & Corkeron, P. (1996). 大堡礁北部儒艮的种群现状。提交给大堡礁海洋公园管理局的报告，汤斯维尔。 2. Marsh, H. & Lawler, I. R. (2002). 大堡礁海洋公园北部儒艮的分布与丰度：2000年11月。GBRMPA研究出版物77。澳大利亚汤斯维尔：大堡礁海洋公园管理局。 3. Marsh, H.D., Hodgson, A., Lawler, I., Grech, A., & Delean, S. (2007) 大堡礁北部与托雷斯海峡儒艮的种群状况、现状、趋势及未来预测：包括关键威胁识别与评估，以及改善其种群现状的可行管理措施评估。海洋与热带科学研究设施报告系列。凯恩斯：珊瑚礁与雨林研究中心有限公司（共77页）。 ## 数据存储位置 本数据集归档于eAtlas永久数据存储库，路径为：dataNERP-TE1.2_GBR-Turtles-dugong-monitoing