FOOD FOR TROUT

Dominion, Volume 13, Issue 110, 3 February 1920, Page 7

FOOD FOR TROUT

CONDITIONS IN THE SOUTHERN . Dr. Tillyard, D.Sc., M.A., F.L.S., F.E.S., Linncan Macleay Fellow in Zoology, University of Sydney, who is nt present engaged iij research work in the Dominion, gavo somo impressions to a "Daily Times" reporter of his tour in> the southern districts. Dr. Tillyard's studies are chiefly concerned with aquatic insects as a food for trout. Ha said that apparently there were now very few trout in Lako Wakatipu, but jpi the other hand they were plentiful 'in the Knwarau River near its outlet from the lake. ' new he found that the fish lived practically solely- on .the dragon fly larvae, which in tho immature stdge live in the water. Tho fish were in excellent condition, as tho dragon fly larvae is one of the best foods in the world for trout. The only drawback was that there were not sufficient species of dragon flies in the district, nnd for that matter there were not sufficient 6pecies right throughout the Dominion. 'V'. 'I'illyp.rd said lie believed that Lake Wakatipu never had any great supply of insect food for trout, the cold lakes being deficient in thi9 resect. The rapid nowing rivers, howevor, had a very good supply of food of this character. Tho rainbow -trout had all disappeared from Lake Wakatipu, but Dr. Tillyard was of opinion that their disappearanco was no great loss. The rainbow was a gormandiser, and if it became established in a river'or lake it "ato_ tho rivers out" in Tio time. It was, indeed, for.tunato, that'the rainbow trout had not thriven in the South Island. It had already ruined the. fisheries in Australia. The brown trout, how-ever, was not pcaiiy such a gross .feeder, an'd lit appeared to be able to obtain sufficient food in the rivers in tho . Otago district to keep it in good condition. Moreoverman angler had to cxercise greater skill to hook a brown trout than vas required to hook his brother rainbow fish.

Asked what step? should be taken to conserve tho supply of insect food, Dr. Tillyard said the authorities should rot m on shoving in fry—over-stocking should be prevented—and the big fish should be taken out of the rivers. Periodically rivers .should' be blocked off. The fish should be 'prevented from gaining -an entrance, ana those in the river should be removed. Of course, this plan could be adopted only in the smaller rivers. It was wonderfnl, said Dr. Tilyard, how the insect life increased m such rivers when this course was adopted. In soiite of the' headwaters of the rivers in Canterbury the insect food Imd been badly eaten out, \and as a consequence tho trout had disappeared. Dr. Tillyard said ho was not altogether satisfied that tho numbers of trout eaten' by shags could be regarded as a curse. Tho slijag always took the weakest 'fish, nnd thus- fopt a river from being overstocked. 'I hp quality of'the fish was also better'maintained. It wafl but ono more illustration of tho survival of tho fittest.

■ New Zealand originally had a vf.ry rich insect fauna of may Hies and caddis flies. These wero the two <ery best foods for trout. His investigations showed, howevor, that in many streams the trout had completely destroyed Hie may fly food. The disappearance of the may fly food was most marked in the streams >n Canterbury. So far as the rivers and streams of Otago were concerned, ho was of opinion that they were supplied with a greater quantity Of insect" food than any other rivers in the Dominion. The f-v this would probably be found In tho fact that tho brown trout were not such keen eaters in the rout hern district, as it was natural far litem to do better In a cold climate. Referring to qttinnat. salmon. Dr. Tillyard said he had learnt that the run of these salmon in the South Canterbury rivers had ceased. Tho quinnat salmon had been most plentiful in the Waitaki River some two or three years ago, but as it was Tecognlsed that they made their appearance in largo numbers onlv every four years, it might, bo expected that they would return in liumbors nt the expiry of that period. 1