N.Z. MARINE DEPARTMENT-FISHERIE,S BULLETIN No. .į

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stream-bed, where gravels are loosely cemented and consolidated. The marking of several series of redds has shown that, even in rivers generally considered to have loose beds, subject to frequent flood movement, redds withstand norm¿,l flood action because relatively stable sites are selected. In most smaller streams studied, the beds were much more stable than in those in which redds were marked. In these smaller streams the possibilities of serious disturbance of redds seemed far less. During winter floods of a severity unknown in at least the preceding 13 years, 27 pet cent. of the salmon redds in a gorgy hill stream, Broken River, were washecl away and a further 19 per cent. were left stranded. These losses took place during what is cornmonly termed in New zealand an "old Man Flood." In two other cases substantial changes in the courses of streams, with consequent damage to redds, followed the entrance of landslip debris into smaller streams. Such happenings are abnormal. Elsewhere abnormal flooding between spawning seasons is known in two cases to have washed away areas of gravel in which fish hacl spawned in many preceding years. Although these areas were not in use when these floods occurred, it is clear from time to time floods of sufñcient severity to destroy redds must sornetimes take place while eggs are in thd redds. It should, however, be noted against these few exceptional cases.- ( 1) \Mith normal flooding, the marking of redds gave negative results in streams selected as being most likely to show flood losses. (2) Although it was a not infrequent happening in the course of five seasons' work to have to abandon operations temporarily because of floods, it was always possible, after subsidence of flood waters, to return ancl continue the excavation of series of redds, even the surface contours of which hacl not been substantially modifred. (3) In most cases the same portions of bed were used year after year in difierent streams. In many of them even the surface contours of many redds made the preceding season were still preserved at the beginning of the next. (4) Inevitably over the years only the progeny of spawners most capable of selecting good sites and burying their eggs efficiently have survivecl; therefore, stocks could not be expected to be found spawning where floocling of usual severity always destroyed their redds. A number of stocks, inclucling some in waters subject to regular heavy flooding, are known to have been maintained for many years solely by local reproduction. on present evidence, floods seem chiefly significant, not in destroying reclcls, but in rendering unstable portions of bed which might otherwise be useä by spa\¡r'ners. The selection of the sparvning iareas and the deep burial of the eggs ensure for most of the eggs a sufiñcient margin of safety from the clirect action of nornral floods. The rnargirr is not, however, sufficiently great to safeguarcl all eggs from the direct effects of abnormal floods in all streams. There are many streams not given to flooding and others where substantial iucreases in volutne are not accompanied by nruch disturbance,of the l-lecl. In them the chances of any considerable number of redds suffering fronr clirect flood actiol seem in sonle cases non-existent and ir, others remote. In other streams, and more especially those with flood-l¡eds in which changes of course take place from tine 761 Fisheries bulletin (N.Z. Marine Dept.) no. 9 (1948)
to time, abnormal flooding, occurring in winter at infrequent intervals, lnay cause very substantial directluÁ"g" and i-esultant flu9!ry!1ns in the density of stocks. SUMMARY OF LOSSES The l0sses cliscusse
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.ç N.Z. MARINE DEPARTMENT-FISHERIE
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Ito -il ,A f { I { tIô i N E W ZEA
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t ta t CONTENTS Part L-Historical I
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? e CONTENTS-Continued' DNiInonuBNr
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Plate t, Text LIST OF' ÍLLUSTRATIO
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PART I Historical INTRODUCTION 1.ur
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(15)Hitherto,restrictionsonangling,
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the transference of fish and had to
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187G80-Releases of brown trout were
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have been successfully introducecl
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poltv'ef, alx1 have clisclntgecl wa
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Reference to forest fires causing h
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shadowed urater, and that the penet
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occurred fairly generally, may be n
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ö drainage has led, it is said, to
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The existing laws, which are a strr
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years ago" from the Lee. In 1883 he
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Orcti Ri 11 (St|. Is.) bct¡-een Di
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eaches of the Oreti the fish were o
Page 39 and 40: iÀr River !Vaipa.hi ....'. tt Slia
Page 41 and 42: N) \o River Lure Period 1880-18m' 1
Page 43 and 44: CHA}{GE I}f SIZE OF TROUT-SOUTH ISL
Page 45 and 46: fr) River Lure Period 1880-1890 189
Page 47 and 48: (¡ of sorle inadequacy of specific
Page 49 and 50: fallen in inverse proportion to the
Page 51 and 52: without a corresponding decrease 'o
Page 53 and 54: the Waipahi, increase in numbers bu
Page 55 and 56: \iVhile the number of anglers has i
Page 57 and 58: cent. in the smaller east and west
Page 59 and 60: Data from the special licensing are
Page 61 and 62: (Above) I)rought conditions at Quad
Page 63 and 64: PART II Recent Management of Fisher
Page 65 and 66: important sources of income in the
Page 67 and 68: v aim 'is solely one of transfer, i
Page 69 and 70: the same as the number of eggs stat
Page 71 and 72: û Exclusive of Taupo and Rotorua t
Page 73 and 74: handled where eggs are collected, a
Page 75 and 76: Í- stage.Subsequentlosses,aSgivenl
Page 77 and 78: L The reports of the Ballarat Fish
Page 79 and 80: J be seen, when abnormal losses are
Page 81 and 82: '] as -to losses in two lots of bro
Page 83 and 84: 715,000 fish distributed. This numb
Page 85 and 86: which those estimates were based an
Page 87 and 88: CONSTRUCTION OF SPAWNING REDDS OF B
Page 89: A con-iparison of losses recorded i
Page 93 and 94: It .n,otrlcl appear fronr the facts
Page 95 and 96: 'I'he fìoocl-trrcached rack in thc
Page 97 and 98: oclies has been devotecl to recorcl
Page 99 and 100: In 1935, which was a peak collectin
Page 101 and 102: of the examìnation ol 2,883 birds
Page 103 and 104: stations in the country in a year.
Page 105 and 106: fry of rainbow trout recorded as re
Page 107 and 108: Ë eggs. The "bag" of the other rvh
Page 109 and 110: (t seasons, have used stationary li
Page 111 and 112: t PART III Recent Investigational W
Page 113 and 114: LAKE ALEXANDRINA_SOUTH CANTERBURY O
Page 115 and 116: TABI-E XIX Duration of Species Size
Page 117 and 118: ti 't becoming available. The short
Page 119 and 120: - is nothing to srlggest that any s
Page 121 and 122: S-inch fingerlings can be pr:oducec
Page 123 and 124: -ì has shown that the estimated to
Page 125 and 126: ,t Its contributiori to the èatch
Page 127 and 128: Discussion The various overseas stu
Page 129 and 130: there are fundamental biological re
Page 131 and 132: lnanagement to leave well alone anc
Page 133 and 134: f of the lakes, where, in the absen
Page 135 and 136: RIVER POLLUTION-Thc photographs ill
Page 137 and 138: If man is to improve the fertility
Page 139 and 140: excess, but to the quantity of t.he
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with incligenons forms only where t
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-È-' e tial increase of trout. Con
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here. At present, it is justifiable
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t- of fish from streams. Under tr)r
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Setti;rg an cel baskct u'hcrc it is
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It will be observed from the forego
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d as the present v/fiter has on the
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Environment Improvement-Physical LI
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(3) \A/here the deficiency of cover
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esselltial. Because, r,vith excessi
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,.) in rivers of considerable size
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( 1) The relative al,seuce of angle
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!r'i11 not necessarily be the optim
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fo¡gariro lìivcr-Iì¿unous rainL
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¿> lin,it to llin. would result in
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egulations can have no general sign
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tìature of this iure nc¡r the rno
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è organization in the provision of
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larger ones. However, larger societ
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L G o 4 equitably to obtain a more
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ç o ç ,) of negative interpretati
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0 õ o paid in licence fees, can le
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I ,} o ê REFERENCES Arrrl, K. R. (
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I Jl f Neeouau, Peur, R., & Slerr*.
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J I APPENDIX A The 1941 Census of t
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!L 't ,APPENDIX B Interference with
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fl tf -ì APPENDIX C Injuries to Tr
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APPENDIX D Claims of Success of Hat
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å t.: I -'l t ta ¡ ,} f (3) Cessa
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maxirnum'density. It is possible al
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N.Z. MARINE DEPARTMENT-FISHERIE,S BULLETIN No. .į

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