Eel protection measures within the Manapouri hydro-electric power scheme, South Island, New Zealand

Freshwater eels are in decline worldwide. In New Zealand, although longfin eels (Anguilla dieffenbachii) and shortfin eels (A. australis) are still amongst the most common freshwater fish species, there are concerns about the scarcity of large specimens. There are also indications that recruitment, especially of the endemic longfins, is declining. To protect stocks of this species, a series of mitigation measures have been implemented at the Manapouri Power Scheme (South Island, New Zealand). These include the release of compensation flows, the reconstruction of a fish pass and a catch and transfer programme for upstream migrating juveniles and adult downstream migrants (silver eels). Acoustic telemetry studies aimed at evaluating and improving interception and/or passage for silver eels show that eels were most active when lake levels were rising. Extended searching behaviour was exhibited, especially near the natural lake outlet, and silver eels appeared reluctant to travel to the opposite side of the lake where the hydropower station is located. Overall, just over half of the 31 silver eels tagged were able to find the natural outlet, and means of improving safe passage, including targeted flow releases and more effective methods of capturing the eels in the lake for transfer downstream, are being considered.