TROUT-FISHING PROBLEMS.

Press, Volume LXVII, Issue 20257, 8 June 1931, Page 16

TROUT-FISHING PROBLEMS.

DETERIORATION OVER YEARS.

PROFESSOR PERCIVAL»S REPORT

The'results of research into the movements of trout in various stream*!, the effects of temperature variation, and ofintensive fishing on the deterioration, of the fish over a number of years are dealt with in a report prepared by Professor E. Pereival for the Freshwater Research Committee. "A striking ignorance -concerning temperature conditions has manifested itself throughout the country," he states. "Observations made personally show the coldest and warmest months to be August and February respectively. It has been found that streams 'eloso together may vary, depending on a number of factors. "The highest temperature I have found in a New Zealand trout stream is 51.4 G. (70.5 1\), in the Kapuni stream in the Hawera district. It is probable that a temperature of this magnitude is not nearly so harmful in a rapidly -moving water as it is in ponded water such as was seen near Lake Te Anau, where, in spite of abundance of'- food material, the rainbow present were stunted and lethargic.

Depreciation and Distribution. "Observations have been made upon the distribution of trout along the length of the stream. It is well known that they move upstream to spawn in shallower waters, either of the main river or of its tributaries. This movement varies in time of occurrence — e.g., in the Oroti river it commences about mid-January, usually in the river Selwyn about mid-March, and in tho North Island rivers apparently after the season closes. Thero is ample evidence that the yearlings, . which have chiefly stayed in the region of their birth, move down stream for a short distance at or -about spawning time, and these in turn take the place of two-year-olds, which again replace three-year-oldta. Although this, actually is modified in several ways,, it indicates the general movement from shallow water to deep water. . "The facts of this migration bear very strongly upon the problem, of depreciation, of which much has been written and said. Much time has been taken in obtaining material for the elucidation of tho problom of tho depreciation of trout fishing. Of first importance is a diary kept by a well-known Southland- angler, Mr Neil Mackay, which extends fully through 4'5 years, and deals almost completely with one river, the Oreti or New River; An examination of the records shows that in-, dependency of any change in lure there was in .this particular area a marked fall in average weight during 1888 to, 1892 from approximately 2slb to a little over lib. This latter weight remained roughly constant until 1903 when it proceeded to fall to fib where it remained with slight fluctuations until about 1914.- A further fall took place then to about lOoz until 1921, when a steady decline set in ending is 1929 with Boz aftor which a slight rise ensued. . ■■ ■ ■ -

Depreciation of .the "The early rapid fall is to bo' Explained by the filling off of old Ash. Data from, other plaees bear this out. The later declines ean bu readily, correlated by an incroase in .the number of per cent, for 1904 to 1908,' approximately 75 per cent, increase from 1918 to' 1931 (nearly 150 per cent., increase on the 1904 figures), and from 1925 to 1929 the'increase was approximately 250 per cent, on the 1904 figures. This, along with the enormous increase in the use of the motor-car and the greatly improved roads, has enabled a very ( great increase in the number of fishing hoard thus acting to shorten the life of the fish. Mr Parrott has shown that the average age of fish caught by anglers in the Oreti and similar Southland rivers and in the Hutt river, which resembles them in many respects both, physically and in the amount of -angling, is a little over 3 yoars. "In the Selwyn river, where fish can more readily be sheltered in the deeper water of the lower Selwyn and in Lake EUesmero, the average is about 5 years, while fish from a back countrf portion of the Hurunui river, practically unflshed, had an average age of about 7 years. The conclusion that" excessive angling does bring about depreciation was amply brought out by a consideration of improvement in accessibility to the back country streams in the Auckland district, and in the Opuha Gorge of the Upper Opihi, where iu 1912-13 "(193 fish), the average was 4.31b; in, 1913-14 (176 fish) 4.11b; 1919-20 (97 fish) 5.41b; 1925-26 (93 fish) 3.81b. The indication is' that the rest during the years 'immediately preceding 1919 gave, the fish time to grow oldar and larger. . The age and growth rate of trout, together with the results of scale investigation, are dealt with in Mr A. W.* Parrott's report. "The results indicate certain interesting variations; occurring ' in the condiiton of thp trout from various rivers," he states. ."For instance, in the Cam, Main Drain, - Styx, the highest condition is reached" about De-, cember or early in January, after which a falling off in condition is. noticed. In the Solwyn, Rakaia, Opihi,, the condition is, on an average, good,, while in Lake Sumner, Lake Slieppard, Upper Hurunui river, the condition is poor. '* He doneludcs with an appeal for scale samples of brown and rainbow trout from a large number of South Island rivers and lakes.