In marine ecosystems, seabird populations are well monitored, thus allowing their use as indicators of system fluctuations at multiple spatio-temporal scales. Population abundance estimates are essential features of any conservation and management measures and initiatives. Population abundances can be used to delineate the distribution range and foraging grounds of species during both breeding and non-breeding periods, with multi-annual monitoring allowing for the inspection of the temporal variability within key marine areas. Taking advantage of long-term monitoring schemes, we examined the annual abundance patterns of the northern gannet Morus bassanus in its southern European migratory flyway. Here, the presence of a topographical feature (i.e. a submarine canyon system) could influence physical processes (e.g. upwelling, alongshore currents, and riverine inputs), thus oceanographically differentiating canyon and shelf ecosystems within a spatially restricted marine area. We assessed seasonal and long-term trend fluctuations of monthly northern gannet abundance using Generalized Additive Mixed Models, yielding only a strong seasonal effect. Moreover, we jointly tested the effect of the phenology and the spatial domain (canyon versus shelf) on northern gannet abundance using Generalised Linear Mixed Models, accounting for the excess of zeros. Northern gannet abundance was higher during the pre-winter and post-winter migration, corresponding to its southward and northward movements in the NE Atlantic, respectively. The effect of the canyon was only detected during the post-winter migration. By age, adult northern gannets were more abundant in some periods of the year (from October to March, including the pre-winter migration, the wintering and the post-winter migration), whereas juveniles and immatures were especially abundant during the pre-winter period. Our results could provide quantitative baseline information of northern gannet spatio-temporal patterns in a migratory and wintering area important for both research and conservation efforts, given the high conservation value of the area within the Natura 2000 network.

中文翻译：

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迁徙越冬区北方塘鹅丰度的时空格局

在海洋生态系统中，海鸟种群受到很好的监测，因此可以将它们用作多个时空尺度的系统波动指标。人口丰度估计是任何保护和管理措施和举措的基本特征。种群丰度可用于划定繁殖和非繁殖期间物种的分布范围和觅食地，并通过多年监测来检查关键海域内的时间变化。利用长期监测计划，我们检查了北部塘鹅 Morus bassanus 在其南欧迁徙路线上的年度丰度模式。在这里，地形特征（即海底峡谷系统）的存在可能会影响物理过程（例如上升流、沿岸水流、和河流输入），从而在空间受限的海洋区域内从海洋学上区分峡谷和陆架生态系统。我们使用广义加性混合模型评估了每月北方塘鹅丰度的季节性和长期趋势波动，仅产生强烈的季节性影响。此外，我们使用广义线性混合模型联合测试了物候学和空间域（峡谷与大陆架）对北部塘鹅丰度的影响，考虑了超过零的情况。在冬季前和冬季后迁移期间，北方塘鹅丰度较高，分别对应于其在东北大西洋向南和向北移动。峡谷的影响仅在冬后迁移期间检测到。按年龄，成年北方塘鹅在一年中的某些时期（10 月至次年 3 月，包括冬前迁徙、越冬和冬后迁徙）更为丰富，而幼体和幼体在冬前时期尤为丰富。鉴于 Natura 2000 网络内该地区的高保护价值，我们的结果可以提供对研究和保护工作都很重要的迁徙和越冬地区北部塘鹅时空模式的定量基线信息。