Bid to restore Taupo fishery

The Conservation Department is considering a first for the wild Taupo fishery _ introducing stocked trout to the fishery.

If it goes ahead, the stocking will be an attempt to restore the Taupo fishery rivers' early rainbow trout spawning run, which has been gradually disappearing over recent years. Where rainbow trout used to run in early- to mid-winter, the bulk of them are now spawning in late spring.

Department of Conservation fishery scientist Michel Dedual says while it is difficult to know why the early rainbow trout run is disappearing as there are likely to be multiple causes, it is possible that brown trout hunting and feeding on juvenile rainbow trout is one of the major causes.

Dr Dedual says one of the approaches being looked at to restore the early rainbow trout run is a one-off stocking programme, using young fish (fry) to restock the rivers.

The most convenient source of young fish would be the Lake Otamangakau trout, which are an early-running fish, although they are slightly different genetically from Taupo fish. Another source could be Rotorua fish, which also spawn from May to July. However, they come from a small genetic pool of fish and may therefore have lost some of the traits necessary to do well in the Taupo fishery.

The main goal of any stocking programme would be to preserve the genetic integrity of Taupo trout, which are unique in the world.

Department of Consevation are presently rearing 30,000 Lake Otamangakau rainbow trout fry at the Tongariro National Trout Centre hatchery, as well as 10,000 slightly larger fish from Rotorua stock until it has done a risk assessment to decide which source of trout is the safest to use. If both are safe, then the young trout will be reared until they reach about 10cm in length. Young rainbow trout of this size will have a better chance of survival as they are less likely to be preyed on by brown trout, and would also be fast enough to prey on smelt or bullies in Lake Taupo.

The fish would also be split into two groups, with one group released in Lake Taupo and the second in the upper Tongariro, Waipa Stream and Whitikau Stream. The stocked fish would be marked so that they could later be monitored through the trap, anglers' bags and fish counts to identify the best release location.

Dr Dedual says manipulating fish populations by stocking is one of the most controversial approaches to fisheries management, as there are many risks associated with it; and in the most serious cases the consequences of stocking have actually led to a smaller number of fish.

He says that Department of Conservation's stocking project would be classed as `restoration stocking' aimed at rebuilding an early rainbow trout run, but routine and on-going stocking in Taupo would be `enhancement' stocking, and would mean the end of the current wild Taupo trout population.

Department of Conservation sought anglers' feedback on stocking through its draft review of the Taupo Sports Fishery Management Plan but Dr Dedual says that out of about 10,000 season licence holders, only 90 submissions (0.9 percent of licence holders) were received, which were split almost equally between those in favour of stocking and those opposed.

``It's always a problem if you only have one or two per cent of the people responding and you have to decide based on that ... what about the 98 percent left? If the anglers don't want it then we won't do it but if they do, then we will, unless there's the danger of altering part of the run.''

The full article is available to read in the current edition of Target Taupo.