Development of design guidelines for a standardised box trap for multispecies fishway efficiency evaluation: Design, effectiveness and injury reduction

An objective comparison of fishway performances is virtually impossible without standardised evaluation methods and equipment. One of the devices most often applied in multispecies fishway evaluation is the box trap, which is site-specifically designed and almost always deployed without testing its effectiveness even though gear bias is common in all passive fish trapping devices. Based on a literature review and extensive expert interviews, we have compiled a set of design criteria, designed and built a box trap and evaluated both its effectiveness and possible causes of fish injuries. The box trap demonstrated species specific (re)capture rates between 70% and 100% (CI 95% ) for all but two of the ten potamodromous species tested. Barbel ( Barbus barbus ), bleak ( Alburnus alburnus ), bream ( Abramis brama ), nase ( Chondrostoma nasus ) and roach ( Rutilus rutilus ) displayed an increase in small tears in fins, but no significant increase in bruises, haemorrhages or scale loss. A second funnel increased tears in fins but no statistically significant improvement of the (re)capture rate (Chi² = 0.29) could be measured. While this box trap will be used for evaluating fishway performance across all navigable rivers in Germany, it is offered as a standardised methodology for broader application throughout and beyond Europe. Adopting a unified measurement instrument would facilitate harmonised data collection and allow for more objective, cross-border comparisons of fishway effectiveness. • Standardised evaluation equipment is needed for multi-species fishway performance • We designed a box trap for use in all medium to large technical fishways • We optimised box trap, funnel dimensions and -materials and reduced handling • Trap efficiency with one funnel was similar to two funnels, but caused less injuries • The box trap demonstrated a recapture rate of 76–98% for the 8 most abundant species