Assessing the current feces identification method of the European otter

Submitted by editor on 5 February 2021.
The European otter on ice with a codfish (Photo: Jan Skriver)

By Liselotte Wesley Anderson on behalf of all authors

The European otter’s (Lutra lutra) elusive and semi-aquatic behavior make monitoring using direct observations of the otters difficult. Therefore searching of otter signs in the field has become the method used worldvide in studies of otter distribution. Especially the visual assessment of otter spraints/feces is known to be difficult, and mistakenly, spraints from mink (Neovison vison) or European polecat (Mustela putorius) can be identified as otters or vice versa. Accordingly, the current practices for identifying feces rely upon skilled evaluation.

Three participants in the laboratory blind test.

The objective of the present study was to validate the survey method used to monitor otters in different regions of Denmark by combining field recognition, identification of spraints in the laboratory by a test-panel of experienced and inexperienced persons, and species identification by DNA-analysis. In brief, 193 samples of spraints and jellies from presumably otter were collected from six different geographical areas in Jutland, Denmark by different collectors based on the technical guidelines for extensive monitoring of otter. A blind test was conducted in the laboratory where nine collectors used visual cues and scent to identify if the feces were from an otter.

Otter sprainting place near to a brook.

The results revealed a mismatch between identification of the spraints as coming from an otter by the participants in the laboratory blind test, the collectors and geographical origin of the feces. In general, we found that the commonly applied identification method was reliable in areas with high population density combined with a prior knowledge of population movements while it loses strength at the fringe of the population distribution. In these areas and in newly discovered areas of otter presence, the method would benefit from a supplementing DNA analysis to validate the species identification. This will increase the effectiveness of monitoring and management programs saving time and resources. 

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