A DNA-based evaluation of North American river otter diet with respect to fishes: Implications for the conservation of aquatic predators and their prey

The North American river otter Lontra canadensis was once widespread in North America but became extinct in the State of Indiana owing to habitat losses and unregulated trapping. However, following reintroduction, the population has expanded markedly since 1995, representing a notable conservation success story.The recent population growth has led to conflict with recreational angling groups who perceive otters as competitors. To investigate the extent of this competition, a DNA-based study was conducted to determine whether material from the stomachs of trapper-harvested otters could be used to identify fish prey species they had eaten.Representative specimens from 33 wild fish species were used as positive controls for DNA assays of otter prey. Mitochondrial DNA barcoding sequences generated from each fish species were used to develop a piscine barcoding assay to identify otter prey species.Fourteen otter carcasses were dissected, and multiple independent DNA extractions and mitochondrial sequencing reactions were performed on the prey bolus from each stomach. The sequences were analysed bioinformatically for taxonomic assignment to prey species.DNA evidence of nearly two dozen fish species, including species of recreational (e.g. bass) or conservation interest (darters) was found in the stomach material.This approach could help to determine the presence of prey species in otter diets, including those fish of conservation concern. That, in turn, would help to determine the best management options for conserving both otters and fish.