IntroductionConservation of cetaceans is challenging due to their large-range, highly-dynamic nature. The EU Habitats Directive (HD) reports 78% of species in ‘unknown’ conservation status, and information on low-density/elusive species such G.griseus, G.melas, Z.cavirostris is the most scattered.MethodsThe FLT-Net programme has regularly collected year-round data along trans-border fixed-transects in the Mediterranean Sea since 2007. Nearly 7,500 cetacean sightings were recorded over 500,000 km of effort with 296 of less-common species. Comparing data across two HD 6-years periods (2013-2019/2008-2012), this study aimed at testing four potential indicators to assess range and habitat short-term trends of G.griseus, G.melas, Z.cavirostris: 1) change in Observed Distributional Range-ODR based on known occurrence, calculated through the Kernel smoother within the effort area; 2) change in Ecological Potential Range-EPR extent, predicted through Spatial Distribution Models; 3) Range Pattern, assessed as overlap and shift of core areas between periods; 4) changes in ODR vs EPR.ResultsMost ODR and EPR confirmed the persistence of known important sites, especially in the Western-Mediterranean. All species, however, exhibit changes in the distribution extent (contraction or expansion) and an offshore shift, possibly indicating exploitation of new areas or avoidance of more impacted ones.DiscussionResults confirmed that the ODR could underestimate the real occupied range, as referring to the effort area only; it can be used to detect trends providing that the spatio-temporal effort scale is representative of species range. The EPR allows generalising species distribution outside the effort area, defining species’ Habitat and the Occupied/Potential Range proportion. To investigate range-trends, EPR needs to be adjusted based also on the Occupied/Potential Range proportion since it could be larger than the occupied range in presence of limiting factors, or smaller, if anthropogenic pressures force the species outside the ecological niche.ConclusionUsing complementary indicators proved valuable to evaluate the significance of changes. The concurrent analysis of more species with similar ecology was also critical to assess whether the detected changes are species-specific or representative of broader trends. The FLT-Net sampling strategy proved adequate for trend assessment in the Western-Mediterranean and Adriatic basins, while more transects are needed to characterize the Central-Mediterranean and Aegean-Levantine ecological variability.

中文翻译：

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地中海低密度鲸类物种范围和栖息地趋势评估测试指标

引言由于鲸类动物分布范围广、动态性高，因此保护它们具有挑战性。欧盟栖息地指令 (HD) 报告了 78% 的物种处于“未知”保护状态，以及有关低密度/难以捉摸物种的信息，例如G.griseus，G.melas，Z.cavirostris自 2007 年以来，FLT-Net 计划定期收集地中海跨界固定横断面的全年数据。在 500,000 公里的努力范围内记录了近 7,500 头鲸目动物，其中有 296 种不太常见的物种。比较两个 HD 6 年期间（2013-2019/2008-2012）的数据，本研究旨在测试四个潜在指标以评估范围和栖息地的短期趋势G.griseus，G.melas，Z.cavirostris: 1) 基于已知事件的观察分布范围-ODR 的变化，通过努力区域内的内核平滑器计算；2) 通过空间分布模型预测的生态潜力范围-EPR 范围的变化；3) Range Pattern，评估为不同时期核心区域的重叠和转移；4) ODR 与 EPR 的变化。结果大多数 ODR 和 EPR 证实了已知重要地点的持续存在，尤其是在西地中海地区。然而，所有物种都表现出分布范围的变化（收缩或扩张）和离岸转移，可能表明开发了新区域或避免了更多受影响的区域。讨论结果证实，ODR 可能低估了实际占据的范围，因为参考仅限努力领域；它可用于检测趋势，前提是时空努力量表代表物种范围。EPR 允许概括工作区外的物种分布，定义物种的栖息地和占据/潜在范围比例。为了调查范围趋势，EPR 还需要根据占用/潜在范围比例进行调整，因为在存在限制因素的情况下它可能大于占用范围，或者如果人为压力迫使物种离开生态位，则它可能小于占用范围。结论使用补充指标证明对评估变化的重要性很有价值。同时分析具有相似生态的更多物种对于评估检测到的变化是特定于物种还是代表更广泛的趋势也至关重要。