Data_Sheet_2_Small Cetacean in a Human High-Use Area: Trends in Harbor Porpoise Abundance in the North Sea Over Two Decades.docx

The North Sea is one of the most heavily used shelf regions worldwide with a diversity of human impacts, including shipping, pollution, fisheries, and offshore constructions. These stressors on the environment can have consequences for marine organisms, such as our study species, the harbor porpoise (Phocoena phocoena), which is regarded as a sentinel species and hence has a high conservation priority in the European Union (EU). As EU member states are obliged to monitor the population status, the present study aims to estimate trends in absolute harbor porpoise abundance in the German North Sea based on almost two decades of aerial surveys (2002–2019) using line-transect methodology. Furthermore, we were interested in trends in three Natura2000 Special Areas of Conservation (SACs), which include the harbor porpoise as designated feature. Trends were estimated for each SAC and two seasons (spring and summer) as well as the complete area of the German North Sea. For the trend analysis we applied a Bayesian framework to a series of replicated visual surveys, allowing to propagate the error structure of the original abundance estimates to the final trend estimate and designed to deal with spatio-temporal heterogeneity and other sources of uncertainty. In general, harbor porpoise abundance decreased in northern areas and increased in the south, such as in the SAC Borkum Reef Ground. A particularly strong decline with a high probability (94.9%) was detected in the core area and main reproduction site in summer, the SAC Sylt Outer Reef (−3.79% per year). The overall trend for the German North Sea revealed a decrease in harbor porpoise abundance over the whole study period (−1.79% per year) with high probability (95.1%). The assessment of these trends in abundance based on systematic monitoring should now form the basis for adaptive management, especially in the SAC Sylt Outer Reef, where the underlying causes and drivers for the large decline remain unknown and deserve further investigation, also in a regional North Sea wide context.

北海是全球人类活动干扰最为频繁的陆架海域之一，兼具多样的人类影响类型，涵盖航运、污染、渔业及近海工程建设。此类环境胁迫会对海洋生物造成负面影响，例如本研究的目标物种——港湾鼠海豚（Phocoena phocoena），该物种被视为海洋生态指示物种（sentinel species），在欧盟（EU）境内拥有极高的保护优先级。欧盟成员国均负有监测该物种种群现状的法定义务，本研究基于2002年至2019年近二十年的航空目视调查数据，采用航线样线法（line-transect methodology），旨在估算德国北海海域内港湾鼠海豚的绝对种群丰度变化趋势。此外，本研究还关注三处以港湾鼠海豚为指定保护对象的Natura2000特别保护区（Special Areas of Conservation，SACs）的种群丰度动态，我们分别针对三处SAC、两个季节（春季与夏季）以及德国北海全域开展了趋势估算。在趋势分析环节，我们采用贝叶斯框架（Bayesian framework）处理一系列重复目视调查数据，该方法可将原始丰度估算的误差结构传递至最终趋势估算结果，同时适配时空异质性及其他不确定性来源。研究结果显示：德国北海北部海域的港湾鼠海豚丰度呈下降趋势，南部海域（如博库姆沙洲特别保护区（SAC Borkum Reef Ground））则呈现上升趋势。在作为核心栖息地与夏季繁殖地的叙特外礁特别保护区（SAC Sylt Outer Reef），我们检测到了概率高达94.9%的显著种群下降，年降幅达3.79%。德国北海全域的总体趋势显示，整个研究期内港湾鼠海豚丰度以每年1.79%的速率持续下降，置信概率达95.1%。基于系统性监测得到的丰度变化趋势评估结果，应成为适应性管理（adaptive management）的核心决策依据，尤其是在叙特外礁特别保护区——该区域种群大规模下降的潜在成因与驱动机制目前仍不明晰，亟需在北海全域范围内开展进一步调查研究。