Taupo Fishery Report

Taupo Times, Volume 11, Issue 77, 8 July 1953, Page 5

Taupo Fishery Report

PRESENTED TO ANGLING CONFERENCE Progress Statement Of Results Of InvestigatiGn A major item in the agenda of the Fourth Annual Wildlife Conference held at Turangi on Saturday last was the presentation by Mr D. F. Hobbs, Senior Fishery Officer, Manne Department, of a report on the research project carried out in the past three years into matters regarding the Taupo Fishery. The report emphasised that a stage had now been reached when it would be possible to predict, in terms of addition or diminution of total yield, the effects of certain possible adjustments. The Taupo investigation was essentially a co-operative undertaking on a bigger and more sustained scale than previously attempted on any locai fresh-water fishery problem in New Zealand.

Plan Of Investigation j Mr Hobbs stated that h6 had been dii'ected by the Minister of Interaal Affairs, the Hon. W. Bodkin to enquire into matters which were causing eoncern regarding the Taupo Fishery. Principally therJe was coneern because of a reported high proportion of ill-conditioned rainbow trout. Questions arose as to whether efopping of the stock was adequate, and as to whether it was taking place at the most suitable time of the year, Available facts were insufficient to enable the questions to be dealt with eonclusively. The investigations were planned to achieve the following results: — 1. An accurate ^ picture of the length, weight, condition and sex of the exploited stock month by month through the season in both lake and tributaries. 2. A measure of the distribution and results of angling efforts as indicated by sample diary records. 3. A reliable picture of the cluration of the spawning seasons, composition of the mature stocks, losses on the spawning grounds, loss of condition of surViving fish and the time of return to the lake. 4. A picture of the distribution of the kelts in the lake, their condition there at subsequent times, the extent to which they show up in successive spawning seasons, and their growth and condition. 5. The location of main spawning grounds and an appreciation of relative quantities of spawners entering different streams. With the exception of the last aim, on which much valuable progress had been made, and on which work was eontinuing, these immediate aims had been substantially achieved, although this phase of the- work would not be completed until late returns for the 1952/53 season, and further data from *the eontinuing trapping programme at the Whareora River has been analysed. Angling Pressure And Yield The Report showed that in the 1951/52 season almost 15,000 licence holdei's at Taupo expended a fishing effort amounting to 87,600 anglerdays. Records of about 2300 days' fishing by different anglers in that season suggest that angling effort was distributed as follows: Tributaries (fly only), 23 per cent.; river mouths (fly only), 32 per cent.; Lake Taupo (mainly trolling), 45 per cent. An average day's angling, as shown by suitable diary records, extended over 4.628 hour's. The estimated percentages of the season's angling effort expended each month of the 1951/52 season, when the Lake season opened November 1st, and tributaries December lst, and closing dates were respectively April 30th and May 31st, werfe: November, 11.2 per cent; December, 16.4 per cent; January, 20.5 per cent; February, 10.1 per cent; March 13.4 per cent; April, 17.7 per cent; May, 10.7 per cent. Possible effects of staggering the season al dates as above had been to close rivers in the month when fish were formerly most abundant^ and vulnerable, and to cause an inconveniently heavy concentration of angling effort on the rivers in May, when fish were less abundant than in November, and when competition between anglers sharply reduces the individual bag. The total catch and kill i*espectivel$ of fish per angling hour as shown b> records of over 10,000 hours were

0.73 and 0.51. If these figures were reliable, then the catch of the 1951/52 season was about 297,000 trout, of which 208,000, or 70 per cent were killed, the balance being released because of poor condition. So far as diary information affords a sound guide, the total kill was distributed as follows: Tributaries, 19 per cent; river mouths, 23 per cent; lake, 58 per cent. Condition Of Trout S'ome interesting points with - regard to size and condition of the rainbow trout were included in the Report. Present infoPmation showed most of the young fish passed into the Lake during their first year of life or soon after, and showed a 50/50 sex ratio, both in the case of fish pondreared fhom Tongariro eggs, and of small samples of wild fingerlings. The relative absence of fish below 18 inches in anglers' captures, and absence of visible evidence of their presence in such clear water, suggests that early gr'owth be made remote from the shore and at a considerable depth in the Lake. A series of samples of rod-caught fish taken in recent years showed evidence of a reduction in size which might still be proceeding, average lengths having been as follows: — 1948/49, 23.9 inches; 1949/50, 22.7 inches; 1951/52, 22.5 inches; 1952/53, 21.9 inches. The pr'ocess of spawning was attended by heavy losses of adults, in the Whareora River about 30 per cent of m&les and 25 per cent of females. It appeared that bigger fish tended to be rather more vulnerable. Ther'e was no reliable evidence that the rainbow trout in Lake Taupo were becoming progressively late spawners. The species was recognised in its original habitat as a spring spawner and its behaviour at Taupo was not I abnormal. There was, however', variation in the time of peak spawning activity, even between different Taupo tributaries, and in the time and duration of spawning activity in different thermal-area lakes. This matter might repav further study. Main Conclusions. Outlining the main conclusions r'eached, the Report states that there is clear evidence of a small and apparently progressive decline in average size of Taupo trout in recent years. This has occurred over a period of gfeatly increasing angling pressure, but definitely does not result from want of opportunity of fish to reach larger sizes simply because they are killed while too young. The size and condition of fish up to the time of first spawning are good by usual standards in this country and elsewherte. The condition of fish is nsually poorer aftef maturity, there being negligible further growth in length, and recovery of condition be1 ing protracted in time and limited in degree. The condition of matured fish may not be abnormal for the species. Relative to the brown trout, however, the protracted spawing season anc lateness of spawning of rainbow at Taupo does not afford sufficient opportunity for recovery of conditior L before the following angling season. Excessive Matured Fish The stock at present includes an excessive and uneconomic proportion oj r matured fish, leading to extravagani r diversion of food from actual growtl (Continued on Page 7)

Taupo Fishery Report

{Continued from Page 5) to mere • maintainance and production of eggs in excess of needs. With careful adjustments of angling pressure, it should prove possible, within limits, to take a greater crop of fish in terms of gross weight, and to increase somewhat the average size of individual fish, the size at maturity and the condition of matured fish, The evidence suggests the need for changes of policy in the direction of planned experimental increases of cropping, and if permanent gain is to be derived this must include provision for observation and measurement of results. Before details of possible adjustments are decided, the Report states, there is need for balanced and specifie information from angler's on a series of matters coming within a broad inteTpretation of the phrase "angling convenience." There may be need ako for' further examination of data in hand. (Note: — See elsewhere in this issue, under the heading "Questions for Anglers," for a summary of information suggested in the above Report as being desirable before changes in Fishery policy are made. — Editor.).