Guts and Glory: Unraveling the Diet of Eurasian Otter ( Lutra lutra ) Populations Using DNA Metabarcoding of Gut Contents

ABSTRACT

The Eurasian otter ( Lutra lutra ) is a semiaquatic, freshwater top predator of conservation concern due to its significant global population decline in the last century. Following its recovery and recolonization in parts of Europe, the population faces ongoing threats, including habitat loss and fragmentation due to human activities, climate change, prey depletion, and exposure to emerging contaminants. Accurately identifying its diet is crucial for understanding ecological interactions and proposing effective management strategies. DNA metabarcoding based on high‐throughput sequencing is a reliable diet analysis tool with better resolution than traditional methods. This study, for the first time, applied two 16S rRNA primers targeting different prey classes on the dietary spectrum of two Eurasian otters populations returning to Northern Germany (Schleswig‐Holstein and Lower Saxony). DNA fragments of prey items from the gut contents of 156 otters collected between 2005 and 2022 were sequenced. Fifty‐five operational taxonomic units (OTUs) were identified in the dietary remains, including freshwater and marine fish, anurans, caudates, and water birds. Otters in the study area are opportunistic predators with wide dietary plasticity, feeding on the most abundant species. Nine‐spined sticklebacks, common roach, and common frogs were important prey items, and marine fish species were detected in the diet of some of the investigated otters. The otters' diet differed between Lower Saxony and Schleswig‐Holstein, between sexes, and a slight difference was observed between adults and subadults. This study provides new insights into the diet composition of otters and their ability to exploit a variety of resources in their habitat. This information is vital for understanding their chances of survival in an environment that is continuously changing due to human impacts and for developing effective management tools.