FISH AND THEIR FOOD

Evening Post, Volume CXVIII, Issue 54, 1 September 1934, Page 11

FISH AND THEIR FOOD

INTERESTING FACTS

FRESH-WATER RESEARCH

LECTURE TO ANGLERS

A largo -attendance of anglers was addressed on Thursday night by Processor Percival, of Canterbury University, on the question of fresh-water fish research. Mr. L. O. 11. Tripp, president of tho Acclimatisation Societies' Association, presided, aud amongst an interested audipnee was his Excellency tho Governor-General, who, at tho close of

the proceedings, strongly' urged the further prosecution of research, aud greater co-ordination amongst the societies in activities tho value of which lie appreciated.

Briefly reviewing early investigations and records from. IS7S, Professor Percival led to tho steps taken for independent action first by tho Wellington Acclimatisation Society in 1927, and by Iho Canterbury Society in 1928, and described tho formation of tho fish research committee in Ohristclmrch, and how, by 1929, support to fish research by societies had become general. It was urgently necessary to accumulate a body of fact upon which to base deductions in view of hitherto fruitless discussions and dogmatism. Depreciation of fish had been evident during tho last 40 years, correlated with an increase in angling and means of transport. Even the general adoption of cycling had an influence on tho numbers of fish taken, and later tho motor ■ increased the toH, while now and improved angling - methods had shortened the average life of the fish population. As tho older fish were generally the larger, tho weights, in tho averago also decreased. In ono stream where a fall prevented the ingress of trout, and the population was restricted-to natural iv- . crease only, there were observed in the same stretch of river 55 spawning beds before the improved angling linethotls • were introduced, as compared with 23 - bods af tor such methods had been in usi? for some time. '■' NO TOOD SHORTAGE. ■ Purveys made had disclosed that as far as trout food in the rivers and lako3 went there was no shortage, in the rivers of the, two islands. Unstable riverbeds, subject to very rapid flow in times of spates, did not harbour the same quantity of trout food as thoso of slower streams.. Trout food, in fact, resolved itself largely into tho extent to which algae and other river bottom . plants provided shelter for the minute organisms which fed on diatoms, etc., and which in turn provided food for sueceedingly larger ones, until these provided the trout food. Geological evidence showed that New Zealand rivers as a whole had had rapid flows rand consequent erosion for raucli longer than was generally thought. Tho Canterbury rivers showed deposits of shingle perhaps 300 feet deep, whereas' at one bridge across the Waimakariri the riverbed had risen only 11 feet since 1860. Other parts of Now Zealand could show similar instances of erosion over thousands of years. . It was often urged that new fish foods from other countries should be introduced into New Zealand streams, but considerably more knowledge of these organisms was necessary before it would bo advisable to make the experiments. In England much money had been wasted in stocking somo rivers with various snails, fresh water shrimps,' etc., which had not thrived^ there. It was necessary to remember that trout were-carnivorous,'and'that the animals ou which trout fed were also carnivorous, deriving their food from organisms that got it from plants, and that tho foods for the smaller organisms mighii determine the presence of obscure foods for such introductions. VANISHED BIG FISH. It was established that depreciation had taken place in the Or.etl. expressed as a reduction in the average weight, correlated with an increase in angling [activity. The'committee had coma to the conclusion that there was a con* . 'slant removal of the higher age grdups "of trout with fishing, but it inusfr ba , remembered that there was a tendency to regard isolated big fish taken in the early years as a standard rather than as an exception. One of tho causes advanced for size deterioration was food conditions. Since tho beginning of 1930 some 130 streams- had been visited, and there was, by and large, no evidence of a shortage of fish food in tho Dominion, • though where waters were enclosed "competifion might become, intense. It was too soon in tho investigations to accept the view that before tho forests wore destroyed there was abundance of fish food where now there was poverty. In, tho;case of may flies he did not think that this was the case because these flies mated at a considerable height above the surface of the ■■•water, and in forest-fringed streams the conditions did not obtain, but generalisations were premature. TALES TOLD BY SCALES. An interesting description of the manner in which age was perceptible from, the scalo rings and the balaneiug stones of the ears of trout was given. Tho summer bands on- scales were laid down between September and February, and up to April, the winter bands from February to April, finishing about the end of August, and tho difference between summer and -winter bands was bound up with physiological changes in the fish, -which > governed growth in length and 'presumably weight. Tho exact influence of heredity, environment, and migration upon growth was not yet definitely ascertained, but it might bo possible, if moid growth were inherent, to produce :i "stock of fast growers. A fast grower at three years might be twice as long as a slow grower of the samo ago. Experiments in migration woro now being made with marked fish. NATUBAL SPAWNING- BEST. "Contrary to the generally accepted belief amongst fish culturists," said ■IM-qfbsso'r Porcival, "tho naturallyspawned eggs are usually highly fertile, fertilisation being chiefly over !)!) per cent. The survival of hatching eggs is also well over 9.0 per cent, in what way be culled ordinary circumstances. Rare instances of losses are by chango in tho course of a" river, and then only in tho heavy shipglo rivers, by tho deposition of. eggs in unsuitable places, by tho disturbance of eggs by subsequent spawners, and by the taking of newly-ejected eggs by other fish in tho neighbourhood, before they are covered. Eggs arc rarely washed away before being covered, as thero is no current in-tho pit itt which' they are laid." ■\jdmpjjring artificial with natural methods, ho said that last year aboufc •4,500,000 eggs were taken from one viver, where 5000 fish were handled. It n*» stated that about 25,000 fish passed ,up the river after the trap was removed, and a conservative estimate, would give 15,0Q0,000 eggs from those fish. It might be possiblo to use favourable streams aa natural hatcheries, from which to draw stocks of young fish for other waters. -. .In conclusion, Professor Percival said that during tho last four years a considerablo amount of work had been done, and if this work were carried, on, tho research committee would be able to present suggestions which would, ho thought, justify a continuance of the work. A series of graphs, and other, slides

was shown to illustrate points made in the address, some of the must interesting of which dealt with tho growth and ages of trout, from tests made in a number of rivers, tho lecturer establishing that for a trout to spawn once it must have reached an average length of 11$ inches. It was also shoiyu how tho trout population varied in preponderating ages according to the season of tho year, tho larger fish often disappearing entirely to return towards the spawning season. Tho pictures shown of the redds, or spawning beds made by the fish, proved that a tremendous amount of shingle in proportion to the size of the fish was removed and replaced. The Chief Inspector of Fisheries (Mr. A. E. Hefford) expressed his gratitude to Professor Percival for tho amount of work he had so thoroughly done, a tremendous task, as anyone acquainted with tho difficulties of the work would appreciate, though it was ia reality only a preliminary skirmish compared with what had been done in other countries. While they owed a great deal to the pioneers of acclimatisation in Now Zealand, the lecturer had shown what could be donb under the more scientific methods of today,.and it was nnly by research and understanding tho laws of Nature'that the fresh-water fisheries could be improved. LORD BLEDISLOE'S VIEWS. The Governor-General, moving a vote of thanks to Professor Pereival, said that on no previous occasion had he hoard ,an eminent biologist dispense to such an extent with technical jargon. He was impressed not so much with the valuable research undoubtedly going on as with the enormous scope which remained for further research. "It seems to me," said his Excellency, "that it is eminently desirable that tho activities of all acclimatisation societies, which aro doing a most valuablo patriotic work, should bo as far as possiblo systematised and co-related on a co-operative basis, so as to render available to tho research worker as much reliable material as is possible, upon which ho can conduct his research. Tho fact stated by Professor Pereival which- impressed me most was that if the fish are left to themselves under natural conditions, something like 97 per cent, of the ova may be expected to hatch out, whereas under artificial conditions a much smaller proportion can be expected. As Mr. Hefford put it, wo should go back to Nature as far as we can, aud make conditions as favourable as possiblo to the successful hatching out of tho ova, rather than attempt to spend any very large amount of money on artificial processes, which aro obviously not so prolific as the natural conditions." Nothing could bo more fatal than the cessation of research, continued Lord Bledisloe. Regarding tho complaints of anglers from tho : Old Country and others that tho fish in New Zealand's famous rivers wero cither smaller or in poorer condition, which ho had noted,, ho said that he had naturally asked experts what the reasons were. The reasons were almost as numerous as tho informants, which seemed to point tho importance of interesting tho Government in.the standard of fishing in this country, which was certainly, in view of the fact that it was known to bo the finest in the- world, a .national problem, if not an Empire, or even a world one. Thanking his Excellency for the kindly interest he had, displayed, Dr. G, Pi V. Anson, chairman of the Wellington Acclimatisation Society, said that Lord Bledisloe had always impressed upon the people of this country the importance of applying scientific methods, and ho hoped he would go back to England with tho news that the anglers of New Zealand wero taking steps' themselves to apply them to their problems.