PROGRESS OF TAUPO TROUT FISHERY RESEARCH

Taupo Times, Volume IV, Issue 203, 16 December 1955, Page 6

PROGRESS OF TAUPO TROUT FISHERY RESEARCH

Review By Mr D. F. Hobbs At I Angling Conference ® An interesting feature of the annual conference between 1 senior Departmental officers and delegates from the fishing and shooting organisations of the Taupo Country, held at Turangi on Thursday, December 8, was a review by Mr D. F. Hobbs, Senior Fishery Officer, of recent investigational pro- W gress. Dealing with the two recent experimental winter fishing ;;|g seasons, and the research work of recent years, Mr Hobbs , S said that there was now a better picture of the Taupo Fishery 3 than probably was obtainable of any other Lake fishery in the | Southern Hemisphere. The former field of conjecture had been; jl enormously narrowed.

Mr Hobbs said that main objects of the 1954 experimental winter season had been to learn the best fishing period as regards both quality and numbers of fish, and the extent of angling interest in May to November fishing; to divert angling effort from | younger immature fish, capable of I making further growth, to older less thrifty fish, thereby improving feeding conditions for the younger; and to effect a limited increase in gross yield of fish taken. Winter Season Results The first winter season (1954) showed that angling pressure in the five winter months was approximately one-quarter of that expended in the seveh months November-May season. Angling pressure which in the open season fell mainly on the lake fish was diverted in the winter to the rivers, thus transferring pressure from the mixture of immature and mature fish in_the Lake to the bigger fish. An estimated 42,000 fish were taken in the winter season. Condition of the fish was well above the open season average. The main reasons for the second winter season suggested that the 1954 winter results might not fairly indicate normal conditions. These were that the 1954 winter season was essentially a personal experiment for every participant; an exceptionally mild winter might have made conditions especially favourable to anglers, and have infiuenced the time when spawners moved to the tributaries. Other factors taken into account in connection with the second winter season, though they had nothing to do with experimental conditions, were that approximately 22,000 additional angling days and 42,000 fish had been provided for interested anglers; and that substantial capital assets employed in transportation, accommodation and provisioning of anglers should not be laid up unnecessarily. The only major adjustment in regulations introduced in the second winter was that the daily bag limit was increased from 5 to the sumner limit* of 8.

Results of the second winter season confirmed those of the first. The yield appeared to have been about 30,000 fish, but when later returns were checked it might approach last season's total of 42,000. Referring to distribution of angling effort, Mr Hobbs said that whereas in the open season 77 per cent. went to the Lake and 23 per cent. to the riyers, in the 1954 winter 27 per cent. was lake fishing and 73 per cent. river fishing, and. in the 1955 winter 33 per cent. was lake and 67 per cent. river fishing. The slight increase in lake fishing in the 1955 winter was probably due to greater efforts in September, and particularly in October, by anglers who had profited by the previous winter's experience. The figures for distribution of angling effort in time over the winter months of 1955 accentuated sharply the concentration of interest in June, and October, figures being as follows: — June 28 per cent., July 17 per cent., August 9 per cent., September 13 per cent., October 33 per cent, . „ Judged by the small percentage of fish rejected by anglers in the 1955 winter, condition was very satisfactory, rejects at 4.2 per cent. being as little in evidence as in the previous winter and well below recent summer figures. The effects of increasing the bag limit from 5 to 8 could be fairly accurately stated. Blank d^vs amounted to about 3 out of 10. The avefage angler on 1 dav in 20 exeeeded the earlier limit ot 5 fi^h. but had onlv

fish in excess of five in daily bags amounted to only 6 per cent. of all captures, and this was an accurate measure of the effect of increasing yi|l the bag limit. Suanmary of Reseajpch Mr Hobbs said that the substantial fl purposes of the two winter seasons fl had been accomplished, and all con- y||8 cerned now had a fairly accurate \tj|| picture of a series of matters had hitherto been simply the subject §l|i of conjecture. This result had been obtained by good team work on the .-.M part of both staff and anglers themselves. The size, condition, movements and • distribution of the larger fish in all months of the year were now fairly accurately known. A valuable appreciation had been obtained of the whereabouts and relative importance of most spawning grounds. The es-. | sential facts as to the migrations and | achievements of the angler himselfilia in different months and di£ferent]M places were now known. A series of "yardsticks" of p,er-;||M manent value for measuring future aM change had resulted. Also of perman-1 ent value had been the training and ^|| development of local staff, until appreciation of the factual approach ||8 had become normal and methods j evolved earlier by scientists had pas- ;> sed into everyday use. Tangible gains to anglers from the research had been considerable, in addition to the ten months additional ^ fishing in the past two years, and in-|ji cluded an extension of the open sea|g son from 7 months (and sometiuies less) to 9 months, with the hope that M this would continue, and the knovrledge that the administration would 1 check all feasible alternatives, before ||| modifying it, should increasing angl- J ing pressure or other causes necessi- ^ tate change. The daily bag limit had been re- :.||B vised upward from 6 to 8 fish; .more ;||g tolerable conditions had been provid-^ ed for boat fishermen, who earlier gM were almost under threat of e victiQn from important trolling grounds;. andj poor conditioned fish had at least | been reduced to below "riuisance | level" and possibly to. the minup.um which could be achieved.

Future Of xaupo risner y ^ No-one could predict with certainty | the future of this great fishery, s^id^ig Mr Hobbs, because knowledge was ^ still very imperfect on a number of / points, especially as to the habits and | food resources of immature fish. ^ Again, nothing was known of factors |i| affecting the seasonal abundance of |i food organisms. . . ■ > *1:811 Licence holders had been increas- ;:i ing at the rate of 1,000 a year at*ig Taupo for the last three years. There | was much lakeside development, andMH the partial sanctuary which the size 'mM of the lake earlier provided was being | invaded by increasing numbers of g| boats. -vr . Thus it might seem somewhat | foolhardy to recommend more gen^ J| erous bag limits and a more generous JI open season than had prevailed for half a century. Yet certain historical || facts warranted that course. When Taupo waters were first stocked fish developed rapidly to vei&.|gj great sizes, but as numbers bicreasea |y size fell until about 1916 to 1918 it reached an all-time "low." Following | a deliberate policy of nettmg to | destroy trout, size "sky-rocketed ht the early 1920's, only to drop baat-a| again at first sharply . and then . || slightly year by year, until the introduction of smelt provided a tempo- v. M rarily higher ''ceiling" again. ,'a If the stock was again reduced sur-;« ficiently it would seem inescapable that the average size of fish, at first M maturity. must go ud. The average "!nno-+-T-i fiu.ring the last ™

| ' i — | most systematic and uniform, had I stayed remarkably constant, overall | figures for lake and tributaries be- | ing: — Season 1951-52, 22.0 inches; I 1952-53, 21.9 inches; 1953-54, 21.9 | inches; 1954-55, 21.8 inches. The frac- | tional change shown might not in £ fact have occurred, as proportions of | fish recorded from lake and rivers | varied somewhat in different years. After discussing data as to per- | centage of mature fish falling into l different main size groups, as shown J by trapping of the Whareroa Stream I and the Tongariro River, Mr Hobbs | said that these data indicated the 1 first type of change to be expected when angling pressure was deliberately directed against the mature stock. Initially, size should go down. If the additional taking of fish had been enough to improve feeding conditions for younger fish, the next change could be toward narrowing of the sixe range, succeeded shortly after by a progressive transfer of fish from lower size groups to higher size groups I if the adjustments made brought I about an increase in size at first | maturity. There was obvious need for con1 tinuing close observations on the size composition of the stock. It was alj so most important that the effects I of natural uncontrollable variables I should not be aggravated by any I policy changes. The type of change | which could prove most confusing j would be the blasting of additional j falls to open out new spawnin£ : grounds. It must, however, be appreciated that two or three successive favour- | able spawning seasons could well add ; sufficient young stock to absorb any j excess of food made available by heavier killing of adult fish. If this occurred (and 1954 had been exceptionally favourable) the anticipated results might not eventuate, but there ; would be the offsetting gain of a | greater number of smaller fish. Referring to the relative survival I rates of brown and rainbow trout in Taupo- waters,) Mr Hobbs said data from the Whareroa trap afforded a striking indication of the relatively higher rate of turnover for rainbow than for brown trout. . Percentages of survival figures of 1955 spawners which had been marked in 19.51, 1952 or 1953 seasons were, for rainbow 11 per cent., and for brown 43 per cent. For rainbow the survival from 1951 had dropped to below 1 per cent and for brown was about 4 per cent. Only 3 per cent. of the rainbow had been marked earlier than 1953 as against 17 per cent. of the brown. Balaneed use of the fisheries resources of the Lake called for relatively heavier exploitation of the brown trout.