Past commercial whaling depleted the humpback whale in the Southern Ocean; however, its population has recovered since hunting was terminated in 1966. Information on abundance is essential not only managing target animals but understanding the ecosystem because the species is one of the main consumers of Antarctic krill. Abundance of this species has not been reported in the eastern Indian sector (80–150°E) of the Southern Ocean since the mid-2000s. A multidisciplinary ecosystem survey focusing on Antarctic krill was conducted in the area by the Japanese research vessel in 2018/19 austral summer. An opportunistic cetacean sighting survey (platform of opportunity (POP) survey) was conducted as part of the survey. Four baleen and five toothed whale species were sighted during the sighting survey. Humpback whales (113 schools/178 animals) were most frequently observed, followed by fin whales (15/36). Abundance of humpback whales was estimated as 22,395 individuals (CV = 0.270, 95 % confidence intervals: 13,310–37,663) based on the design-based line transect method. Krill consumption by humpback whales in this area was tentatively estimated as 1.336 million tons, corresponding to 30.9 % of krill biomass, although the amount varied greatly depending on the consumption rate’s assumption. The estimated abundance was comparable with previous estimates, however, there are some caveats in interpreting the results. As no approaching whale sightings were made during this POP survey, the proportion of sightings of unidentified large whales was high, possibly leading to an underestimation of the abundance. Dedicated sighting surveys are desirable to obtain more accurate and unbiased abundance estimates, especially for management purposes, although the results of this study could be used for ecological studies in combination with other data sets recoded by the multidisciplinary survey.

中文翻译：

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2018/19 年南大洋印度东部海域座头鲸的丰度，使用机会性目击调查数据，并注明其他鲸目动物的出现情况


过去的商业捕鲸活动导致南大洋的座头鲸数量减少。然而，自 1966 年狩猎终止以来，其数量已有所恢复。丰度信息不仅对于管理目标动物至关重要，而且对于了解生态系统也至关重要，因为该物种是南极磷虾的主要消费者之一。自 2000 年代中期以来，南大洋印度东部地区（东经 80-150°）尚未有该物种丰富的报道。 2018/2019年夏季，日本科考船在该地区进行了一项以南极磷虾为重点的多学科生态系统调查。作为调查的一部分，进行了机会性鲸类目击调查（机会平台（POP）调查）。在目击调查中发现了四种须鲸和五种齿鲸。最常观察到座头鲸（113 群/178 只动物），其次是长须鲸 (15/36)。根据基于设计的线样线方法，座头鲸的数量估计为 22,395 头（CV = 0.270，95% 置信区间：13,310–37,663）。该地区座头鲸的磷虾消耗量初步估计为 133.6 万吨，相当于磷虾生物量的 30.9%，但根据消耗率的假设，消耗量差异很大。估计的丰度与之前的估计相当，但是，在解释结果时存在一些注意事项。由于在这次 POP 调查中没有发现鲸鱼靠近，因此目击不明大型鲸鱼的比例很高，可能导致对丰度的低估。 尽管这项研究的结果可以与多学科调查记录的其他数据集结合起来用于生态研究，但仍需要专门的目击调查来获得更准确和公正的丰度估计，特别是出于管理目的。