Freshwater fish recovery

Throughout the summer months, irrigation plays a critical role in the production of food and fibre. However, in autumn, when the irrigation season ends, there is no need to divert water into the schemes’ intake channels as the scheme shuts down for winter maintenance.

CPWL’s operations play a significant role in sustaining economic growth locally and nationally. Effective resource management balances the relationship between societal development and the conservation of the natural environment.

The CPWL freshwater fish recovery plan covers the exclusion and protection of freshwater fish at the scheme intakes on both the Rakaia and Waimakariri Rivers. Fish exclusion incorporates structures, such as fish screens or bunds, and fish bypass channels, which have been designed to accommodate known freshwater fish behaviours. These measures have the fundamental purpose of preventing freshwater fish from entering or taking up habitat in the intake areas and minimising the exposure of freshwater fish to physical harm or predation.

Before winter maintenance can begin, the intakes on both rivers are shut down, in a process we call ‘dewatering’. This involves a gradual reduction in water flow as dewatering begins at each intake. This gradual process allows most of the remaining freshwater fish in the channels to migrate naturally with the water’s flow, minimising stress to the fish by funnelling them back into the river through a fish bypass channel.

As water levels in the intake channels continue to lower, any fish that have not returned with the water flow back to the river are captured by nets and manually returned to the flowing river braids. Fish species data is collected and recorded before the fish are returned.

The final step of this rescue work uses a technique called ‘electrofishing’, where the fish are temporarily stunned with an electric charge in the water before being netted and safely returned to the river. Data is again collected throughout the process.

All CPWL protocols for freshwater fish salvage and recovery have been developed in consultation with NIWA, including assessment to identify and implement the most appropriate methodologies. CPWL also has a specialist staff member trained in electrofishing who is supported during fish recovery events by CPWL’s operations team. This helps the team to learn and better understand fish behaviour and to incorporate this knowledge into their general intake operations work.

Fish salvage and recovery Rakaia Intake – Total 73

• Upland Bully (Gobiomorphus breviceps) – 4
• Unidentified Bully – 36
• Longfin Eel Ōrea (Anguilla dieffenbachii) – 9
• Unidentified Eel – 17
• Lamprey Kanakana (Geotria australis) – 1
• Brown Trout – 2
• Salmon – 4

Fish salvage and recovery Waimakariri Intake – Total 671

• Torrentfish Panoko, (Cheimarrichthys fosteri) – 309
• Common Bully Toitoi (Gobiomorphus cotidianus) – 214
• Longfin Eel Ōrea (Anguilla dieffenbachii) – 36
• Shortfin Eel hikumutu (Anguilla australis) – 2
• Unidentified Eel – 7
• Kōaro (Galaxias brevipinnis) – 1
• Lamprey Kanakana (Geotria australis) Brown Trout – 1
• Rainbow Trout – 60
• Salmon – 41