Many of New Zealand’s native fish are migratory and require unimpeded access to and from the sea to complete their lifecycles. Ecological studies have documented effects on native fish in relation to the operation of flood protection schemes in New Zealand, including direct mortality when fish travel through the pumps, effects which are amplified during the downstream migration season.
The Waikato Regional Council (WRC) is responsible for the maintenance and operation of flood control schemes which were installed over 50 years ago, focusing on maximising the rate of floodwater clearance and with little consideration to ecological impacts. There is growing awareness of the potential impacts of such schemes on native freshwater fish, particularly freshwater eels (tuna, Anguilla spp.).
WRC’s ‘Pathways to the Sea (PTTS) Project’ was established to better understand the impacts of its’ flood control infrastructure on fish passage, investigate new approaches to improve downstream fish passage (particularly eels) at flood pumps, and to develop a strategy to guide future decision making around management of new and existing infrastructure. WRC have installed a FishFlow Innovations Encased Archimedes Screw Pump (EASP), the first pump of its type installed in New Zealand. The EASP has been reported as having very little impact on fish that pass through it, but it has not been assessed on New Zealand eel species which tend to grow larger than other anguillids. As part of the PTTS, the performance of the EASP will be monitored. The objectives of the monitoring are to, i) assess the mortality/injury rate of eels passing through the EASP, ii) determine the size ranges of eels that can be safely passed by the EASP and iii) assess whether there is any pump avoidance exhibited by eels. Monitoring will be undertaken during the 2023 migration season with results presented at the conference.