2021-01, Krieg, Raphael, King, Alex, Zenker, Armin

The spread of non-indigenous crayfish species poses a threat to local populations of crayfish as well as to other fauna and flora across Europe and around the world. Several methods have been used in attempt to reduce their numbers and stop their further spread. Crayfish barriers are the best way to stop the non-anthropogenic spread of established invasive crayfish populations. Up to now there are very few published papers regarding crayfish barrier design and practical experience in construction. For the last seven years, we have optimised construction and functionality of crayfish barriers, tested various building materials and planned construction of many barriers across Switzerland. In this article, we highlight our experience, share the acquired knowledge and present the newest findings regarding considerations, which must be made when planning a barrier to stop the upstream movement of non-indigenous crayfish species. From our experience we conclude that crayfish barriers work in preventing the movement of invasive species if certain factors are taken into account. Barrier design and construction must be specific for each project, because the size of the watercourse, flow velocity, bank conditions, existing constructions and accessibility, all change the way a barrier should be set-up.

2020-06-04, Krieg, Raphael, Zenker, Armin

Invasive non-indigenous crayfish species (NICS) are a global threat to local flora and fauna. Total eradication of an entire population of invasive NICS is a difficult task; several methods have been tested and are still being used, with varying success. Most methods reduce population size and control the species within the targeted area but do not majorly prevent further spread of NICS. However, construction of crayfish barriers can stop the spread of NICS and can therefore, be used to protect indigenous crayfish species (ICS). There are currently very few published scientific papers about this topic. This review reflects current knowledge on how to stop migration when NICS are established and provides useful information for the construction of barriers. The most important findings related to building a crayfish barrier are: the need for a vertical wall with an overhanging lip above the water surface; smooth sections to prevent crayfish from walking or climbing over the obstacle, combined with flow velocities of 0.65 m/s act as a barrier within the waterbody. Additionally, modifications to existing structures, bridges, culverts and dams reduce costs and increase effectiveness in stopping upstream migration of NICS. Barriers can negatively impact certain aquatic species, mainly benthic and slow swimming fish by preventing their migration and genetic exchange. However, they can have positive impacts for ICS and other indigenous organisms against the negative effects of NICS. Local legislation should support barrier construction to prevent the spread of invasive crayfish and other aquatic invaders to protect ark sites for ICS.