The Otter Has a Hard Time in Switzerland

The Eurasian otter is returning to Switzerland and is set to become permanently established here in the long term. A solid understanding of the occurrence, distribution, and population trends of any species is a crucial foundation for its protection and promotion. Mapping surveys are therefore among the most fundamental tasks in species conservation.

Since 2011, the presence of otters along the Aare between Thun and Bern in the canton of Bern has been documented. Since 2014, offspring have been repeatedly observed there. In 2017, the Pro Lutra Foundation, WWF Bern, and WWF Solothurn launched the "Otterspotter" project. With the help of volunteers, the project aims to record the distribution of the Eurasian otter in the cantons of Bern and Solothurn on a two-year cycle.

In the first survey during the winter of 2017/18, watercourses within 73 grid squares of 5×5 kilometres were examined. Eurasian otters were confirmed in nine of these squares.

The second Otterspotter survey was carried out in the winter of 2019/20. A total of 37 Otterspotters searched for otter tracks across 80 grid squares. Otter tracks were discovered in seven of these squares. In four of those seven squares, otters had already been confirmed during the winter of 2017/18, while the remaining three squares represent first-time confirmations within the Otterspotter project. However, no evidence was found this time in five squares where otter tracks had been discovered during the first survey.

Between the two surveys, a change in area use was observed: the presence along the Alte Aare was no longer confirmed, while at least one otter was newly detected at Wohlensee. This highlights how important close-knit documentation is for gaining a better understanding of the otter's spread. A third survey in 2021/22 is being pursued.

Ottersare territorial and are considered largely solitary, at least in flowing waters. Young animals must therefore leave their mother's home range at the age of nine to thirteen months and establish their own territory. Genetic studies suggest that young otters prefer to settle near their place of birth. Under favorable conditions, the otter population can expand by four to twenty kilometers of river length. However, where otter populations are low, recovery is slow. This is due in part to the long rearing period of over a year, as well as the generally high mortality rate of young animals in their first year of life.

The cautious return of the otter to Switzerland has meant that the species is no longer listed as extinct on the national Red List, but “merely” as critically endangered. The goal is now a healthy and long-term otter population in Switzerland. An important foundation for the protection and promotion of the species is sound knowledge of its occurrence, distribution, and population trends. This information is also indispensable when resolving conflict situations that may arise around the otter. Surveys are therefore among the most fundamental tasks in species conservation. At the same time, thorough and timely surveys provide important information about how otters spread into new areas and which habitats they preferentially seek out for recolonization, writes theStiftung Pro Lutra.

The Eurasian otter was hunted in Switzerland for decades for its exceptionally dense fur. It was considered a competitor of fishermen, and a law from 1889 actively promoted its extermination. In 1952, it was placed under protection — but this was too late to save it. Since 1989, it has been considered extinct in Switzerland. For just over ten years, it has been spotted in Switzerland with increasing frequency. To establish itself in the long term, living waterways with a healthy fish population are the primary requirement.