Over the last 25 years, the harbour porpoise (Phocoena phocoena) has made a significant return to the Southern Bight of the North Sea and the English Channel due to a shift in distribution from northerly regions. Although the ecological drivers of this return are unclear, this species faces multiple threats in the region, including by-catch and habitat degradation. Ferry-based surveys were conducted year-round between November 2011 and June 2014 to assess the influence of environmental parameters upon the spatiotemporal distribution and relative abundance of harbour porpoises in the Southern Bight of the North Sea. A total of 1450 sightings of harbour porpoises were recorded during the 100 round-trip surveys carried out between Dunkirk (France) and Dover (England). Inter-annual and monthly variations in group size were observed, with largest groups recorded in 2014 (mean = 2.02) and in January (mean = 2.32). The relative abundance showed significant seasonal variation, with peaks recorded during winter months. An inter-annual increasing relative abundance was recorded during the study period. There was a seasonally dependent association with environmental variables, particularly depth, seabed roughness and current speed. Finally, predictions suggest large increases of the relative abundance in offshore habitats during winter months and over the study period.

中文翻译：

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使用机会平台数据模拟北海南湾港湾江豚的精细分布和相对丰度

在过去的 25 年里，港湾江豚 (凤尾藻) 由于分布从北部地区转移，已显着返回北海南部海湾和英吉利海峡。尽管这种回归的生态驱动因素尚不清楚，但该物种在该地区面临着多重威胁，包括副渔获物和栖息地退化。在 2011 年 11 月至 2014 年 6 月期间，全年进行了以渡轮为基础的调查，以评估环境参数对北海南湾港湾鼠海豚时空分布和相对丰度的影响。在敦刻尔克（法国）和多佛尔（英格兰）之间进行的 100 次往返调查中，共记录了 1450 次港湾鼠海豚的目击记录。观察到群体规模的年际和月度变化，最大的群体记录在 2014 年（平均值 = 2.02）和 1 月（平均值 = 2.32）。相对丰度显示出显着的季节性变化，在冬季月份记录到​​峰值。在研究期间记录了年际增加的相对丰度。与环境变量，特别是深度、海床粗糙度和海流速度之间存在季节性关联。最后，预测表明，在冬季和研究期间，近海栖息地的相对丰度会大幅增加。