Fish injury and mortality at pumping stations: a comparison of conventional and fish-friendly pumps

Pumping of water during floods from hinterland drainage systems into the main river poses a health risk to fishes and comparative studies are crucial to identify the most fish-friendly pump designs and operations. We investigated the effects on fish health of pump passages through four conventional and one 'fish-friendly' pump. All pump types caused external fish injuries leading to direct and delayed mortality. Immediate mortality and injury intensity increased with revolutions per minute (rpm) and differed significantly (P < 0.05) between pump types. At the 'fish-friendly' Pentair pump (Fairbanks Nijhuis, London, UK), higher numbers of injuries resulting from blunt force (e.g. haemorrhage, scale loss and fin tears) were detected than at the conventional pumps, potentially due to the differences in blade design. The Koster pump (Koster, Heide, Germany) at low rpm proved to be similarly fish friendly as the specially developed fish-friendly Pentair pump due to the low number of entrained fishes. As a measure to reduce potential damaging to fishes, the pumps should run on low rpm as often as possible. This lowers the risk of collision with machine parts and hence mortality rate, as well as the suction effects see at high rpm. After long periods in an anergic state, pumps should generally run on low rpm before changing to higher rates.