Standardized test procedures
In their investigation into the environmental situation at the shaft power plant in the Loisach, the research team followed a standardized procedure in releasing several thousand fish from eight species typical to Bavaria upstream from the hydropower plant. After the fish passed the installation, they were captured in large nets stretched across the watercourse, along with wild fish also living in the river. The researchers then examined the fish for signs of injury, including taking X-ray images to check for internal injuries. They also deployed sensors to examine the forces to which the fish are subjected when passing the power plant.
Only 21% of the fish released upstream and recaptured downstream from the power plant passed through the openings in the weir, while 75% traveled through the turbine shaft. The remaining 4% used the lateral fish ladders. The grill – a grate covering the shaft – allowed larger fish to pass through than had been thought possible (longer than 30 centimeters). The median mortality rate for all species of fish that passed the turbine was 13%. The highest mortality rate of 44% was recorded for roach while the turbine was subject to low load. The lowest mortality rate of less than 1% was recorded for grayling and brown trout while the turbine was subject to high load. A significant number of other fish were also injured. Of the wild fish captured during the study, 47% passed through the openings in the weir, 35% through the shaft and 18% via the fish ladder.