Abstract Knowledge on spatial and seasonal distribution of species is crucial when designing protected areas and implementing management actions. The Baltic Proper harbour porpoise (Phocoena phocoena) population is critically endangered, and its distribution is virtually unknown. Here, we used passive acoustic monitoring and species distribution models to describe the spatial and seasonal distribution of harbour porpoises in the Baltic Proper. Porpoise click detectors were deployed over a systematic grid of 297 stations in eight countries from April 2011 through July 2013. Generalized additive models were used to describe the monthly probability of detecting porpoise clicks as a function of spatially-referenced covariates and time. During the reproductive season, two main areas of high probability of porpoise detection were identified. One of those areas, situated on and around the offshore banks in the Baltic Proper, is clearly separated from the known distribution range of the Belt Sea population during breeding season, suggesting this is an important breeding ground for the Baltic Proper population. We commend the designation of this area as a marine protected area and recommend Baltic Sea countries to also protect areas in the southern Baltic Sea and the Hano Bight where additional important harbour porpoise habitats were identified. Further conservation measures should be carried out based on analyses of overlap between harbour porpoise distribution and potentially harmful anthropogenic activities. Our study shows that large-scale systematic monitoring using novel techniques can give important insights on the distribution of low-density populations, and that international cooperation is pivotal when studying transnationally migratory species.

中文翻译：

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波罗的海港湾鼠海豚的盆地规模分布为有效的保护行动提供了基础

摘要 在设计保护区和实施管理行动时，了解物种的空间和季节分布至关重要。波罗的海港湾鼠海豚 (Phocoena phocoena) 种群极度濒危，其分布几乎未知。在这里，我们使用被动声学监测和物种分布模型来描述波罗的海地区港湾鼠海豚的空间和季节分布。从 2011 年 4 月到 2013 年 7 月，海豚点击检测器部署在由 8 个国家/地区的 297 个站点组成的系统网格上。广义相加模型用于描述检测到鼠海豚点击的月概率作为空间参考协变量和时间的函数。在繁殖季节，确定了两个主要的海豚发现高概率区域。其中一个区域位于波罗的海沿岸及其周围，在繁殖季节与已知的带海种群分布范围明显分开，表明这是波罗的海沿岸种群的重要繁殖地。我们赞扬将该地区指定为海洋保护区，并建议波罗的海国家也保护波罗的海南部和河诺湾的地区，这些地区发现了其他重要的港湾鼠海豚栖息地。应根据对港湾鼠海豚分布与潜在有害人为活动之间的重叠分析，采取进一步的保护措施。我们的研究表明，使用新技术进行大规模系统监测可以对低密度人口的分布提供重要的见解，