Assessment of predation on small semi-aquatic mammals by the Eurasian otter through genetic analysis of spraints

Abstract Small semi-aquatic mammals play a critical role in the river ecosystem and can be used as bioindicators of environmental health. Many populations of these species are threatened by multiple factors, mainly habitat degradation, but also by other causes such as predation. Among potential predators, the Eurasian otter ( Lutra lutra ) is known to prey on some of these species, but the significance of the impact on their populations remains uncertain. To study the effect of the Eurasian otter on the small semi-aquatic mammal community, we collected feces containing hair remains from different rivers in the Iberian Peninsula and used genetic methods to identify the predator and prey species. We identified 83 Eurasian otter spraints containing 25 Iberian desmans ( Galemys pyrenaicus ), 21 Iberian water shrews ( Neomys anomalus ), and 28 Southern water voles ( Arvicola sapidus ). These prey species were recorded in different watersheds throughout the study area and over a long period of time, indicating their widespread presence in the otter diet. These findings are of particular concern for the Iberian desman, given its endangered status. Our results highlight the need to specifically investigate less abundant but ecologically significant groups consumed by the otter, such as semi-aquatic mammals, to better understand the influence of this predator on the riparian ecosystem. In addition, future efforts should address the genetic analysis of feces containing hair remains from different riparian carnivores to assess the impact of predation on the viability of semi-aquatic mammal populations.