The Otter Way of Wildlife Management--Developing Otter-Friendly Exits from Fish Traps in Collaboration with Stakeholders

In most parts of Europe, the European otter (Lutra lutra) has been eradicated due to intensive habitat destruction and hunting. In the early 70ies, the otter became protected by law in Germany and restoration of habitats... [ view full abstract ]

In most parts of Europe, the European otter (Lutra lutra) has been eradicated due to intensive habitat destruction and hunting. In the early 70ies, the otter became protected by law in Germany and restoration of habitats became more and more common. Thus, this species started to recolonize most parts of its former distribution area. The otter population slowly but constantly spreads out from the eastern parts to the western parts of the country. Consequently, human-wildlife conflicts are arising. Otters are at risk of getting trapped in fish traps, which are commonly used in fishery in northern Germany. To date there is no possibility for otters to escape from conventional fish traps. Thus, an otter-friendly way of using fish traps is needed.

In the past, fishers were supposed to use so called fish trap grids. These grids were placed at the entry of the fish trap and prevented otters from diving into it, at the cost of reduced fishing outcome.

We evaluated other possibilities to prevent otters from drowning in fish traps. We tested two different exit systems to be integrated into the third section of a common fish trap. The first system is constructed as a rubber band tear seam. The second system consists of two metal holders that are held together with a spring. Both exit systems are supposed to open at working loads bigger than 1.3 kg. Otters are known to bring up such working load and shall be able to escape, but fish are expected to stay in the fish trap. 

We used N=12 otters in a total of fourteen trials – five trials for the tear seam and seven trials for the metal holder exit. The fish trap was placed in the pool of an otter exhibit and the animals swam in the fish trap via a net tube. It is known for sure, that otters can stay under water for more than two minutes. That’s why every trial was limited to max 120 seconds. In twelve trials, otters escaped easily from the fish trap after a time period ranging from 11 seconds up to 70 seconds with an average escape time of 21,29 seconds for the tear seam and 32,8 seconds for the metal holder. Two trials had to be cancelled because the animal showed abnormal behavior.  

Both exit types were proofed to be useful to prevent otters from drowning in fish traps. As all those tests were conducted together with the stakeholders, we hope that these exits will be accepted and used wide spread in fishery.