ROD AND GUN Civilisation Affecting Taupo Fishing

Press, Volume CVI, Issue 31135, 11 August 1966, Page 7

ROD AND GUN Civilisation Affecting Taupo Fishing

(By J. SIERS.) "The Taupo fishery Is a national asset which does not require great capital cost to run in its present status. It provides angling and recreation for many thousands of New Zealanders, who each year are obtaining more leisure as our standard of living improves. It is a source of valuable foreign exchange as recently there has been a great increase in the number of overseas people fishing these waters.” This is an extract from a report by the conservator of wildlife, Rotorua, Mr P. J. Burstall, which has been circulated to members of the Tongariro and Lake Taupo Anglers’ Club and it goes on to point to the dilemma highly civilised western man is creating for himself in his environment. Mr Burstall says: “There are at least 1,500,0001 b of rainbow trout harvested each year from Lake Taupo. (Sportsmen take about 700 tons by this reckoning.) The value of this fishery to the nation is estimated conservatively at £2,000,000 annually in direct and indirect revenue. In 1964-65 41,500 licences were sold. “The trout stock of this lake is self-supporting from the natural spawning in the streams entering the lake. “Trout spawn in these streams and require loose gravel from pea-size to 3in in diameter. The requirements are critical. It’s necessary for some subterranean water to flow through the gravel to provide life-giving oxygen to the eggs which have been buried by the hen fish. Hatching Percentage “Research has shown that under perfect conditions 90-98 per cent of these eggs are fertilised and that between 85 and 95 per cent, having enjoyed good conditions, will hatch. At 50 deg F. the eggs will hatch in approximately 32 days. After hatching, the young alvins utilise food reserves in their umbilical sec and oxygen found in suspension in the water. Twenty-five days after hatching they emerge from the gravel as fry and then search for natural food at the marginal reaches of the stream. “Research has shown that in this latter 30-day period, the greatest mortality takes place. This is a normal loss and nature has provided for this by determining the number of eggs deposited by each female. Acceptable losses in the wild range as high as 95 per cent and even with losses as high as this a normal fishery can be sustained. Danger From Flooding “The greatest danger to the survival of these eggs and young fish is from flooding. Flooding tends to blanket the redds with silt and the eggs are suffocated. Also the eggs are disturbed by the shifting of gravel during the floods. Flooding will also inhibit the growth of minute organisms which the young fish require to feed on after leaving the redds. Flooding with its resultant accelerated erosion tends to blanket the beds of the stream, not only jeopardising spawning but also limiting the productivity of bottom fauna.

“Young trbut that survive to 2in in length also feed considerably on insects of terrestial origin and should the natural canopy bordering streams be removed the food value of a stream will be lowered, regardless of whether flooding takes .place or not. Good fisheries management requires unspoiled canopies along maryins of streams.

“My department is also concerned about the planting of willows on stream banks in order to retard bank erosion. We feel that an alternative tree must be found. In many parts of New Zealand willows which are planted to retard erosion, have on reaching maturity greatly increased their range and have in the long term the opposite effect. Willow Harmful “They have choked up streams: they have made it impossible for watercourses to carry and convey sediment and water during times of normal flooding and they have completely matted the beds of streams and lowered the flood production of the stream. “This has resulted in a lowering of the fishery values and created improved conditions for predators. They have restricted access and usage of the waters, not only for anglers, but for boating, swimmers and shooters and finally their cost of removal has more than offset the installation costs and the shortterm advantages they provided. Deterioration Noted

“We have noticed over the years that there has been a progressive deterioration in the watershed since the advent of land development and milling and roading. Land development has had the greatest

Impact. Stock gaining access to the water has done considerable damage to the eggs deposited in spawning beds. Increased run-off due to the removal of marginal canopy has resulted in a continual moving of silt down the beds of streams and a typical example of a flood from one inch of rain in 24 hours, which formerly rose the river 18in and dirtied the water for four days, now raises the river 3 feet and lasts for at least a week and brings down more bed sediment than in earlier floods. If this is to continue and the same pattern emerges in all streams which are important spawning areas, it is highly probable that it will not be lon 7 before this fishery will lose its ability to maintain itself through natural facilities. “Should my department be faced with having to s'ock the Taupo fishery with introductions of hatchery fingerlings such as we do in the Rotorua area, we would have the capital costs running into many thousands of pounds, of which we would not be financially capable. “For example: To maintain the Rotorua Lakes we release 150,000 fingerlings with a capital cost of the hatchery at £50,000 and annual running costs of £5OOO. If we had to undertake this work at Taupo on the same basis we would be faced with a capital cost of £200,000 and an operating cost of £30,000 annually to produce a minimum of one 'million fingerlings.”