For The Angler Value Of Surveys

Press, Volume CII, Issue 30289, 15 November 1963, Page 22

For The Angler Value Of Surveys

[Specially written tor "The Press” by J. SIERS]

A superficial examination of a New Zealand river shows a population predominantly of eels, or trout, or both, according to locality. But a river from source to sea can carry up to 15 different species of fish, including brown trout, rainbow trout, perch, eels (two species) salmon, fontinalis, bullies, inanga, flounder, mullet, kahawhai, snapper and cod as well as freshwater pipis, native crayfish or koura and an American species of catfish. Most of the species are limited geographically to a specific part of a stream and are generally dominated either by the predacious trout or the eel. But a small trout, if it survives the jaws of a bully, still has to compete with a host of the smaller living organisms in a stream for its daily food. This can be important from the point of view of its development into maturity and the trout’s subsequent growth as an adult. Yet each river and stream seems to cascade with paradoxes and contradictions of a carefully worked-out standard.

The logic is simple: give trout food, shelter, the right water temperature, alkalinity, plenty of dissolved oxygen and the species will thrive. But this is not alw’ays so. An experiment carried out on the Hinds river showed very few fish in one section of the river where the bottom count of fauna was very high. The survey of the river also showed there is no apparent correlation between cover and fish number or size, although in areas of little cover there was seldom a high trout density. Where the greatest numbers of native fish were found, there were correspondingly high trout numbers.

In these localities native fish were found to comprise 40 per cent of the trout diet. In the same stream there is a lagoon, fed by the river, where high densities of trout were found, but here snails and the mollusc type of foods formed 80 per cent of the fishes' diet. In the upper North Branch of the Hinds river, where the density of trout is sparse, the individual size is large, with trout up to eight and a half pounds. In the lower third of the river, where the density is high, few fish taken weighed over one and a half pounds. The mouth and the lagoon were subject to runs from sea-run trout and these were invariably bigger than the locals. The benefit of this research information for those who want to fish the river is: in the upper reaches you will find few fish, but they will be large; in the lower reaches there are a lot of fish, of a smaller size.