The Bohai Sea is an important distribution zone for the temperate population of finless porpoises. However, very few reports has been published on the finless porpoise population in the region. Six surveys were conducted between May to July 2015 and in September and November of 2016. They were based on the line-transect methods in the Bohai Sea. These surveys were meant to explore population status of the finless porpoise in Bohai Sea, which could provide basic data to develop ecological protection strategies for the finless porpoise in the sea. The total effective trackline length of six surveys was 8972 km. A total of 136 individuals and 87 groups of finless porpoises were witnessed. More finless porpoises were observed near the Yellow River estuary, to the northeast of the Qinhuangdao and in the coast of Laizhou Bay. Of the witnessed groups, sightings occurred more at between 14:00–18:00, in the area 15–35 km offshore. Spatially, the finless porpoise can be found in most of the Bohai Sea, including the three bays and central waters. Of the seasons surveyed, the finless porpoise groups were observed frequently in the waters 20–40 km out of the Yellow River estuary in May. The probability values of group sightings on the trackline were 0.399, 0.085 and 1 respectively in Distance 7.0 software, The finless porpoise population number in the whole Bohai Sea was estimated to number 7883(CV=0.21), 3701(CV=0.21), and 3124(CV=0.21) individuals, and its population density was estimated to be 1.441, 0.066, and 0.056 individuals/km² correspondingly. Compared with those in the southern Yellow Sea and the Inland Sea of Japan, the population density of finless porpoise in the Bohai Sea was relatively smaller. Limited by uncertain effects from the weather, sea conditions and observers’ experience, the estimated values given above need to be confirmed in the future. However, despite the current deficient state of the data, the size of the population of finless porpoise in the Bohai Sea was here estimated for the first time and this work could serve as a reference for future study.

渤海是黄渤海江豚种群的重要分布区，但是有关该区域江豚的种群数量的资料极其匮乏。2015年至2016年，采用截线抽样法在渤海水域开展了6个航次的目视调查，收集了渤海江豚的分布数据，首次评估了区域内的江豚种群数量，为制定有效的渤海江豚种群生态保护策略提供了基础资料。调查结果显示，在2015年8月、2016年5~7月、9月和11月进行的6个调查航次共计8972 km的有效航程中，发现江豚87次、136头次。江豚在渤海各海湾和中部水域都可观察到；14:00-18:00时段、离岸15~35km范围内较易观察到江豚；黄河口外、秦皇岛东北侧老龙口和莱州外沿岸河口水域，江豚出现频次较多。各季节中，以5月在黄河口外20~40km范围内发现江豚的频次和数量最多。采用Distance 7.0软件估算渤海江豚种群数量，其中探测概率分别取值0.399、0.85和1时，渤海江豚种群数量估算值分别为7883头（CV=0.21）、3701头（CV=0.21）和3124头（CV=0.21），对应的种群密度分别为1.441头/km2、0.066头/km²和0.056头/km²，均低于已报道的南黄海和日本海江豚种群相应值。受海上天气、调查条件和经验所限，本文估值可能存在偏差，但限于渤海江豚历史资料缺乏的现状，本文的结果对于认识渤海江豚的种群状况仍具有重要参考意义。