Fishing: Lake Taupo's trout reserves not as deep as once thought

The continuing acoustic transmitter study of the travel of trout around Lake Taupo has blown away the widely held belief that there is a stock of fish well down in the 190m-deep lake.

It was always thought that over-fishing the lake was well-nigh impossible and that the whole stock was safe because any depletion of those near the surface could be replenished by the deep-swimming fish.

But tracking shows that fish spend the majority of their time in the top two to five metres of the lake and rarely go below 20m, and so are available to anglers year-round.

Their movements are governed by chasing food and they will move into temperature zones warmer and colder than their optimum.

The Taupo rainbows spend 90 per cent of the time in water ranging between 11C and 18C. In water that is too hot they can suffer asphyxia as they struggle for oxygen and above 23C they are dead. In cold water their metabolism slows and so does growth.

Fish try to spend as much time as possible in water where feeding and growth rates are best. So knowing where they are likely to be will aid anglers.

In December the water they like is near the shore. By January it has moved to the middle of the lake.

Trout prefer water at 15-16C in summer and that is in the 2-5m zone. But they regularly move up to the 18-19C water right on the surface, particularly early morning and in the evening, to feed on smelt.

By March-April the water generally has warmed more and trout have moved out and down to the 5-10m layer, the data collected by the Department of Conservation and the National Institute of Water and Atmospheric Research shows.

The water at the right temperature is concentrated in a small area and depth range and so are the fish.

The study notes that anglers may have to find "a very narrow depth range to be successful but equally once they find the right depth they make some exceptional catches".

In late autumn, the fish are heading for water around 11C at river mouths, congregating ready to spawn.

In winter, the water layers have mixed and the lake is a uniform 11C. The fish are well spread.

That is the case on the lake at present, reports Jared Goedhart of the Sporting Life store at Turangi.

Deep jigging with 40g Black Magic lures in silver and silver/blue is still producing fish.

Fly-fishers had caught some nice browns in recent days at the mouths but the rivers need more volume in them, he said.

The Sporting Life boys had an April Fool's Day laugh at the expense of followers of their website, displaying a 24-pound rainbow trout supposedly caught on the Tongariro River by Irishman Jim Watts, a regular visitor known in the region, which gave the story and photo credence.

In fact the fish was caught by Watts on a trip to Canada and is a steelhead trout from which the Taupo stock is descended. Their story that the famous Breakaway Pool has reappeared after recent floods is a fiction.

And anyone wondering about the truth in both items should have been alerted by the advertisement for whitebait filleting knives that followed.

The successful Taupo trout monitoring programme is being transplanted to the Rotorua lakes this year, with some Lake Rotorua rainbows already fitted with the acoustic transmitters.

Another survey from Taupo also debunks a myth. It appears that contrary to popular belief that boat numbers were growing, there has been little change since 1993/94 and if anything a slight decline. Around 204 boats were on the lake fishing at fly-over monitoring times over the summer holiday period.

Snapper fishing remains hot, with reds spread over the range of habitats and water columns as the post-spawning feed-up continues.

The catch rate around Auckland appears to be better than that in the Bay of Plenty or the Far North.

Fishing the first Surtees Boats contest out of Whakatane last weekend, we caught terakihi in deep water, rat kingfish in 20m and snapper in the shallows off Whale Island. The snapper catch was patchy and a fish of just 7kg won top prize among the 209 anglers.

Marlin are still being taken there, at Cuvier and around Great Barrier.