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

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ivers in a trapping season þossibiy oiten exceeded the peak intake of eggs by all }trew Zealand hatcheries of about 20,000,000. WASTAGE OF EGGS OF FiSH TRAPPED AND STRIPPED The general effects of trapping on whole spawning runs and the nature of conclitions below traps and the possible extent of the ensuing loss have been indicated. More definite data are available as regards the smaller number of fish actually trappecl and stripped. It is shown in Appendix B that such fish in the Selwyn yield to the strippers greatly less than their total production of eggs. In the lJpukerora and Eglinton in Southland, rrost fish handled are partially spent. 'l'he yield in the Selwyn is less, because approximately one-third of the eggs l-rave l¡een shecl below the traps under conclitions which afford a very slight cl-rance of survival. It is also less l¡ecause approximately 11 per cent. of the eggs the frsh contain when they enter the trap are not removed by stripping. There is no eviclence that the trout attenrpt to spawn these resiclual eggs, and, as the strippect fish ale released below the traps, the eggs would have a very poor chance o[ surviving if they were deposited. - Losses in Hatcheries <strong>No</strong> data are availal¡le from which the extent of losses in New Zealand hatcheries generally could l¡e ascertained with precision. It is not the practice to publisli each year clata on losses at any one hatchery. It is not possible, therefore, to sturcly losses at a nurnbel of typical hatcheries over a sufiñcient series of years to shou' the norrnal variation in loss. In nrany cases releases of fish are stated to equal in nurlber the eggs collected or plrrchased. Only sotnetimes, when the teleases are stated to be fewer than the number of eggs handled, does it appear that a reasonably careful attempt has been macle to determine the extent of loss. For instance, it has been necessary to avoid periods where releases vary from year to )'ear {rorn cluantities sometimes even in excess, sonretimes the same, ancl sonretimes less tl-ran the quantities of eggs received. Again, sometimes a figure has lteen given for total losses, without difierentiation, where the hatchery proclucts have l¡een clisposed of in part as eyed ova, ir.r part as fry, and in part as older fish. I)espitc the imperfections of many ofÊcial reports, examination of a large nutnber has brought to light clata of considerable indicative valne. These clata are presentèd subjcct to the comment that, fc¡r reasons to be giveu, the estimates of average loss clerivecl frour them are likely to be couservative. For 'lrusiness purposes, a numl¡er of supplying societies have nlacle a practice crf aclcliug 10 per cent. or more to the tluantities orclerecl. Purchasing societies dcr ¡9t object to this, ar-rcl in tllany cases may be Llnaware of it, as their official recorcls usually r.nention the cluantity orderecl rather than the larger cluantity usually ,.,.eiu..11 A consigrrnrent exirninecl by the lvriter provecl to be 23 per cent. in excess oI the c¡rantity orclerecl. 1-he Wlungarei Society inforurs ure that'three of four consignments orclered in 1938 were each i0 per cent. ovet ancl the other 12 per cent. over the cluantity orderecl. These consignments came frotu three clifferent strppliers. It r,vill be eviclent that where the quantity of fry proclucecl is tneasured, the dilïere¡ce ltetween this number and the nttmlter of eggs orderecl will be less than the ¿rctual loss if surplus eggs have been supplied, Eggs are purchased at the eyed 60] Fisheries bulletin (N.Z. Marine Dept.) no. 9 (1948) r¡
Í- stage.Subsequentlosses,aSgivenlaterinthissection,arefrequentiybasedon the clifference between numbers of eggs orclered and of fry produced' They are' therefore, possibly under-estimated' A further point arises. Whence come the aclditional eggs, where recorded total collectio* b"l"tt.. the surn of sales' lc ties statecl to have been sold are uncler-stat shorved that some years ago, at one collectecl was ahvays grossly uncler-s cover some of the t* ín to the eyecl stage, and to enable goocl measure to be given to purchasers' In this particular case' receipts of eggs were actually 25 per cent' in excess of the cluantity recorclecl' To what extent this pr".,lá was general, or: still obtains' is not known' Anextrernecaseoffalsificatiorro{recorclsocctrrredwlrerrlgaveacarefulll' an acclimatization society' He reportecl the quantity I gave him' The council' the quantiiy again, so that an original is no eviclence that practices as extreme for regarcling the figures for loss given than over-stated' rearing of fish through the sumnrer 'r,vas supplied in personal col1ìmunlties, ale inclicated by asterisks' Lossesextraorc]inarilylreavyforauyparticularlratcl-reryhavebeenexcltrdecl at this stage, as it is iesirecl frrst to cår-rsicler losses under nortlral cofrclitions' Subsecluently, 'ft" i'"t *"ty "f allnormal losses rvill be considered' EXTET,TT 01ì NC)R\{AL HATCHE,RY LOSSES losscs of Prc-e5ted Ozla'-fn until the ruost vulnerable stage can lte seen. 'lhey are then sttll thtee feet into rvater' tWeak eggs ar infertile.**, or.r.iìiï"*-" op",-1.t" ancl i-r-ray reaclily be separated' The losses con- '"ft-o'ot siclerecl here are of clyi"g before ancl retroved shortly following "ytits -th-o-se testing. Data on these losses are given in Table XII' Fisheries bulletin (N.Z. Marine Dept.) no. 9 (1948) [6i
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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
Page 23 and 24: Reference to forest fires causing h
Page 25 and 26: shadowed urater, and that the penet
Page 27 and 28: occurred fairly generally, may be n
Page 29 and 30: ö drainage has led, it is said, to
Page 31 and 32: The existing laws, which are a strr
Page 33 and 34: years ago" from the Lee. In 1883 he
Page 35 and 36: Orcti Ri 11 (St|. Is.) bct¡-een Di
Page 37 and 38: 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: handled where eggs are collected, a
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 and 90: A con-iparison of losses recorded i
Page 91 and 92: to time, abnormal flooding, occurri
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
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,t Its contributiori to the èatch
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Discussion The various overseas stu
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there are fundamental biological re
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lnanagement to leave well alone anc
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f of the lakes, where, in the absen
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RIVER POLLUTION-Thc photographs ill
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If man is to improve the fertility
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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
Page 179 and 180:
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. (
Page 187 and 188:
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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