Otter diet in reservoirs is known to experience seasonal changes. We selected a reservoir with a large population of exclusively wintering great cormorants and seasonal changes in stored water volume to test the relative influence of abiotic and biotic factors on otter foraging ecology. DNA metabarcoding of otter spraints revealed a dietary change from autumn to winter. Otters had a diet dominated by the exotic goldfish in autumn, but predated intensively on the native northern straight-mouth nase in winter. This change was likely caused by predation of cormorants on goldfish and to fish biology. Secondly, macroscopic analysis of spraints revealed that otters shifted from a diet dominated by fish (in terms of biomass) to a diet dominated by red swamp crayfish during spring–summer, when the latter became overabundant. As revealed by modelling, this second shift was most likely influenced by the sudden increase in stored water volume in spring, but also by the cumulative effect of cormorant predation on fish during autumn–winter. Macroscopic analyses of otter spraints collected in a second reservoir with no cormorants revealed a lack of seasonality. Hence, the combined influence of both biotic and abiotic factors explained otter diet seasonality in a lentic-water novel ecosystem.

中文翻译：

---

季节性变化的水库中欧亚水獭（Lutra lutra）饮食的决定因素

众所周知，水库中的水獭饮食会经历季节性变化。我们选择了一个拥有大量专门越冬大鸬鹚和蓄水量季节性变化的水库，以测试非生物和生物因素对水獭觅食生态的相对影响。水獭扭伤的 DNA 元条形码揭示了从秋季到冬季的饮食变化。水獭在秋季的饮食以异国情调的金鱼为主，但在冬季则密集地捕食北方本土的直嘴鼻。这种变化可能是由鸬鹚捕食金鱼和鱼类生物学引起的。其次，对扭伤的宏观分析表明，水獭在春夏季从以鱼类为主的饮食（就生物量而言）转变为以红沼泽小龙虾为主的饮食，当时后者变得过多。正如建模所揭示的那样，第二个转变很可能受到春季蓄水量突然增加的影响，但也受到秋冬季鸬鹚捕食鱼类的累积效应的影响。在没有鸬鹚的第二个水库中收集的水獭扭伤的宏观分析显示缺乏季节性。因此，生物和非生物因素的综合影响解释了静水新生态系统中水獭饮食的季节性。