12 July 2016

Hundreds of trout return to refurbished spawning race in the Waitaki Hydro system

After the first full refurbishment work since 1968, the Aviemore spawning race is attracting hundreds of brown and rainbow trout and providing more habitat for them to breed in.

The Aviemore spawning race is a 1000 metre long artificial stream channel, constructed in 1968 to provide spawning grounds for brown and rainbow trout in Lake Waitaki. Sockeye salmon also use the race irregularly.

It was built to compensate for the loss of natural spawning grounds that resulted from construction of the Aviemore Dam and uses water from Lake Aviemore which is discharged through the auxiliary turbine in the dam.

The Lake Waitaki trout fishery is reliant on the spawning race as the lakes inflowing tributary streams only offer small spawning areas and only in years with above average rainfall.

Fish & Game Central South Island Officer Jayde Couper oversees the maintenance of the spawning race in the interests of its sports fishing licence holders and was the main driver of the project.

Since 1968 the area of effective spawning gravels bed has reduced, requiring a full refurbishment of the race to the reinstate the spawning area.

The race is owned by Meridian Energy Limited, who partnered with Fish & Game to ensure the future of the Lake Waitaki trout fishery through the ongoing operation of the spawning race.

Meridian contributed more than $30,000 to the work, the refurbishment works were undertaken in April prior to the 2016 brown and rainbow trout spawning season which traditionally occurs from May to October.

Over seven days and using heavy machinery the works involved the removal of riparian vegetation and pest plants to widen the channel width to 5 metres, sieving and de-silting of existing gravels for re-use, instalment of 450 cubic metres of new spawning gravels, the grooming and levelling of gravels to a depth of 0.5 metres which is designed to provide a spawning area for up to 2,000 0.9kg trout.

An early spawning survey undertaken by Fish & Game staff revealed that around 300 brown and rainbow trout are already spawning the refurbished spawning race. Further spawning surveys are planned throughout the spawning season.

Fish & Game Officer Jayde Couper says the improvements are clear to see. “At a glance the works have resulted in a five-fold increase in spawning area which should result in a significant increase in the number of juvenile fish being produced in the spawning race. In 2 to 3 years when these fish reach maturity, anglers should catch more fish”.

Meridian’s Environmental Strategy Manager Jeff Page, says its pleasing results of the gravel refreshment project are already apparent. “We’ve heard there are upwards of 300 trout spawning in the race, which is an excellent outcome.”

“By working in partnership with Fish and Game we’ve been able to preserve and enhance fishing stocks, as part of ensuring the ongoing efficient operation of the Waitaki hydro lake.”

Angler use surveys undertaken by NIWA reveal that the Lake Waitaki fishery gets around 3,000-5,000 angler visits per year.

How do trout spawn?
Female trout ‘dig’ holes in stream gravels by turning on their side and thrusting their tail. They lay eggs in the hole and the male fish ejects milt on to the eggs to fertilise them. The female then ‘digs’ a new hole in front of the eggs which covers the eggs in gravel. The excavations are called redds, which simply means trout nest.

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