Knowledge of a population’s abundance is of primary importance for conservation management. However, robust estimates of abundance are often difficult to obtain, especially for cetaceans which spend most of their lives submerged. Cetacean abundance is commonly estimated using aerial or vessel-based line transect surveys and distance sampling methods. During 2012–2014, the first line transect surveys to estimate cetacean abundance were conducted in Namibian waters. Surveys took place in the Namibian Islands’ Marine Protected Area (NIMPA), a large MPA located along the southern Namibian coastline. A combined visual and acoustic double-platform survey configuration was used to investigate the factors affecting detectability of the endemic Heaviside’s dolphin (Cephalorhynchus heavisidii) and dusky dolphin (Lagenorhynchus obscurus obscurus). The present analysis estimates the probability of detection on the transect line (g(0)) for these two species and generates density and abundance estimates which incorporate a correction for both animals missed on the transect line and attractive responsive movement. The average annual baseline density and abundance estimates for Heaviside’s dolphins in the NIMPA region during 2012–2014 were 0.08 individuals/km2 (CV = 28.6%, 95% CI = 0.04–0.15 individuals/km2) and 1594 individuals (CV = 28.6%, 95% CI = 776–3275), respectively. The average annual baseline density and abundance estimates for dusky dolphins in the NIMPA region during 2012–2014 were 0.16 individuals/km2 (CV = 26.2%, 95% CI = 0.10–0.28 individuals/km2) and 3493 individuals (CV = 26.2%, 95% CI: 2015–6052), respectively. A discussion on the distribution of Heaviside’s and dusky dolphins is provided for this region where such information is urgently needed. Based on existing knowledge of the species and area, these estimates are regarded as reasonable. They indicate moderate sized populations of animals within the NIMPA and provide an important first baseline on which future estimates can build.

中文翻译：

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使用新的视觉和声学线横断面调查对纳米比亚附近的 Heaviside's (Cephalorhynchus heavisidii) 和 Dusky (Lagenorhynchus obscurus) 海豚的首次丰度估计

了解种群数量对保护管理至关重要。然而，对丰度的可靠估计通常很难获得，特别是对于一生大部分时间都在水下的鲸目动物。鲸类丰度通常使用基于航空或船舶的线状横断面调查和距离采样方法进行估计。2012-2014 年期间，在纳米比亚水域进行了第一线样带调查，以估计鲸类动物的丰度。调查在纳米比亚群岛的海洋保护区 (NIMPA) 进行，这是一个位于纳米比亚南部海岸线的大型海洋保护区。结合视觉和听觉双平台调查配置用于调查影响地方性黑海豚 (Cephalorhynchus heavisidii) 和暗黑海豚 (Lagenorhynchus obscurus obscurus) 可探测性的因素。目前的分析估计了这两个物种在横断线上 (g(0)) 上检测到的概率，并生成了密度和丰度估计，其中包括对横断线上错过的两种动物的校正和有吸引力的响应运动。2012-2014 年 NIMPA 地区海维赛德海豚的年平均基线密度和丰度估计值为 0.08 只/平方公里（CV = 28.6%，95% CI = 0.04-0.15 只/平方公里）和 1594 只（CV = 28.6%， 95% CI = 776–3275)，分别。2012-2014 年期间，NIMPA 地区暗色海豚的年平均基线密度和丰度估计值为 0.16 只/平方公里（CV = 26.2%，95% CI = 0.10-0.28 只/平方公里）和 3493 只（CV = 26.2%， 95% 置信区间：2015-6052），分别。为该地区急需此类信息的地区提供了有关赫维赛德海豚和昏暗海豚分布的讨论。根据对物种和地区的现有知识，这些估计被认为是合理的。它们表明了 NIMPA 内的中等规模的动物种群，并提供了一个重要的第一个基线，未来的估计可以在此基础上进行。