Trout Stocks in the Pukaki and Ohau Hydro Canals

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No. 130 Trout stocks in the Pukaki and Ohau hydro canals

ISSN 01I3-25M

New Zealand, Freshwater Fisheries Report No. 130

Trout stocks in the Pukaki and Ohau hydro canals

by S. Bloomberg E. Graynoth

Report to: Electricorp

Freshrvater Fisheries Centre MAF Fisheries CHRISTCIIT]RCH

S ervicing freshtva t er fi she ri e s and aquaculture

September 799t NEW ZEALAND FRESHWATER FISHERIES REPORTS

This report is one of a series issued by the Freshwater Fisheries Centre, MAF Fisheries. The series is issued under the following criteria:

(t) Copies are issued free only to organisations which have commissionedthe investigation reported on. They will be issued to other organisations on request. A schedule of reports and their costs is available from the librarian.

(2) Organisations may apply to the librarian to be put on the mailing list to receive all reports as they are published. An invoice will be sent for each new publication.

ISBN 0-477-08445-r

Edited by: S.F. Davis

The studies documented in this report hâve been funded by the Electricity Corporation of New Zealand Limited.

ill INISiRY OF AGRICIJLTURE ANO FISHEB'ES T: ivlÀNATU AH Ur¿VH EN UÂ ÀHlJM0A¡JÂ

MAF Fisheries is the fìsherìes business group of the New Zealand Ministry of Agriculture and Fishe¡ies. The name ìr{AF Fisheries was tbrmalised on I November 1989 and replaces MAFFish, which was established on I April 1987. It combines the tunctions of the tbrmer Fisheries Research and Fisheries Management Divisions, and the tisheries functions of the former Economics Division.

T1le New Zealand Freshwater FÌsheries Report series continues the Nevv Zealand Minisnl of Agriculture and Fisheries, Fßheries Environmental Report series.

Enquiries to: The Librarian Freshwater Fisheries Centre lvfAF Fisheries PO Box 8324 Riccarton, Christchurch New Ze¿land CONTENTS Page

SUMMARY

1. INTRODUCTION

2. STUDY AREA

3. METHODS 7

4. BROWN AND RAINBO\M TROUT 8

4.t Species Composition 8

4.2 Abundanee aud Distribution 8

4.3 Recruitment and Movements 9

4.4 I-ength, Weight, and Condition Factor 9

4.5 Age and Growth 10

4.6 Diet 12

5. NATIVE FISH T4

6. DISCUSSION l4

7. ACKNOWLEDGEMENTS t7

8. LITERATURE CITED l7

TABLES

1. Physical tèatures of the Pukaki and Ohau canals 't

2. Fyke net catches in the Pukâki and Ohau canals, June 1983 to June 1984 8

J. Seine net catches in the Pukaki and Ohau canals, June 1983 to May 1984 9

4. Numbers and size of brown and rainbow trout observed by divers in three sections of tbe Ohau Canal 9 on 2l February 1984

5. Details of tagged trout which were recaptured in nets or by anglers T2

Freshwater Fisheries Centre Page

6. Mean length, weight, and condition factor of brown (BT) and rainbow (RT) trout caught in fyke and 12 seine nets in the Pukaki and Ohau canals

7. Size composition of brown aud rainbow trout in the Ohau Canal based on fyke and seine net catches and 14 drift-dive counts

8. Relationship between condition factor and length of trout in the Pukaki and Ohau canals, 1983-84 14

9. Mean back-calculated length at age for trout netted in the Pukaki and Ohau canals 14

10. Diet of trout in the Pukaki and Ohau canals 15

11. Comparison of trout stocks in the Pukaki and Ohau canals with other waters in the upper Waitaki 16 catchment

FIGURES

1. The Pukaki and Ohau canals showing fyke and seine netting sites 6

2. Cross section of the Pukaki and Ohau canals 10

3. Correlation between fyke net catch rate and f'low volume in the Pukaki and Ohau canals 1l

4. Length tiequency distribution of brown and rainbow trout caught by fyke and seine nets in the Pukaki 13 and Ohau canals

Freshrvater Fisheries Centre SIJMMARY power stations and into I-ake Benmore. The first stage of the canal system was completeÃ in 19'77 when water was diverted into the Tekapo Canal. The Pukaki and The Pukaki and Ohau canals were netted and drift dived Ohau canals were constructed soon afte¡ and now carry from June 1983 to June 1984 to assess their fish stocks water from I¡kes Pukaki aud Ohau to Ohau A power aud value as a fishery. They coutained brown and station at the head of I¿ke Ruataniwha. The canal rainbow trout and four species of native fish: common system was finally completed in 1985 when the outflow bully, upland bully, koaro, and longfinned eel. Brown from l¿ke Ruataniwha was diverted through Ohau B trout comprisedS2To of the total catch and outnumbered and Ohau C canals into the Haldon arm of Lake rainbow trout in both canals. Benmore.

Seine net catch rates were extrapolated to give estimates The canals have become naturally stocked with brown of 13 trout/hectare in the Ohau Canal and 15 trout/ and rainbow trout from upstream lakes and have hectare in the Pukaki Canal. Drift dive counts were developed into popular recreational fisheries. They are thought to unde¡estimate numbers of trout in the Ohau easily accessible by road and open to fishing all year Canal because there were not enough divers to cover round. Angler catch rates are reasonably high the whole width of the canal. Trout appeared to be (Bloomberg et aI. 1983) and it has been suggested that evenly distributed along the length of both canals. the canals compensate for the loss of the Ohau River which was effectively dewatered when water from I-ake The canal bed is unsuitable for trout spawning, which Ohau was diverted into the canal system (Graynoth suggests that canal stocks are maintained by fish moving le84). downstream from I-akes Pukaki and Ohau. The fish stocks and fisheries of canals have been well Brown trout (mean length : 320 mm, mean weight : studied overseas (Hynes L97O), however very little is 430 g) were slightly larger than rainbow trout (mean known about the fisheries aspects of canals in New length : 296 mm, mean weight : 375 g). The mean Zealand. The aim of this study was to collect condition factor of brown and rainbow trout was very intbrmation on brown and rainbow trout stocks in the low (102 and 108, respectively). Pukaki and Ohau canals to gain a better understanding of the fish stocks and fisheries of canals in this country. Sixty-two percent of trout netted in the canals were The presence of native fish species iu the Pukaki and estimated to be aged 2 or 3 years, although ages ranged Ohau canals was documented and the value of the canal from 1 to 10 years. The percentage of trout aged 1 fishery was assessed. year was relatively low (7%), possibly because many juveniles reared in upstream lakes and rivers. This study was part of a five-year research programme, designed to investigate the impact of hydro-electric The slow growth rate of trout in the canals is thought to power development on the fish stocks and fisheries of be the result of a lack of food and instream cover. the upper Waitaki catchment. Benthic invertebrates were scarce in the canals and winged terrestrial insects were abundant only in the spring and summer. Small fish did not appear to be an 2. STUDY AREA important prey item.

Compared to many upper Waitaki lakes and rivers, the The Pukaki and Ohau canals are situated north-west of canals supported moderate numbers of mostly medium- Twizel township in the MacKenzie basin of the South sized trout in poor condition. The canals are unlikely Island (Fig. l). They are constructed of glacial outwash to be rated highly by anglers and do not compensate for gravel embankments, lined with compacted, clayey the loss of the Ohau River due to hydro-electric power gravels and au outer layer ofcompacted coarse gravels. development. The canals' dimensions are given in Table 1.

Flow in the canals is regulated by control gates at the 1.' INITRODUCTION outlet of Lakes Pukaki and Ohau. Flow volume depends on the demand for electricity and on lake levels, and is usually greatest at 0700 hours and The upper Waitaki catchment has been modihed between 1700 and 1900 hours on week days. Flows are extensively by hydro-electric power development generally higher in spring in the Ohau Canal and in (Fig. 1) (James 1985). A t'eature of this development autumn and winter in the Pukaki Canal (Electricorp has been the construction of alarge canal system which flow records). carries water from upstream Iakes through a series of

Freshwater Fisheries Centre Ohou ¡\ Powerhouse Pukoki Dom/

Loke Ruotoniwho

Ohou B Powerhouse

Ohou C Po*erhouse-

Loke Benmore

IIIGURE 1. The Pukaki and ohau canals showing fyke and seine neuing sites. TABLE 1. Physical featr¡res of the Pulcaki and Ohau Fyke and seine netted trout r¡/ere identified, measured to canals. the nearest mm (fork lengtå), and weighed to within l0 g if they were longer thau 200 mm or tåe nearest gram if they were less than, or equal to, 200 mm fork Pukaki Ohau length. Trout greater than 300 mm fork length were Canal Canal tagged just below the dorsal fin with a serially numbered Floy anchor tag. Tags had a Fisheries l,ength ftn) l3 8.25 Research Division address printed on them so that Water surface width (m) 7t 45.5 recapture details could be sent by anglers to MAF. Water depth (m) 10 5.8 Native fishes were identified and released. Maximum flow volume (m3ls) 4Æ 170 Gradient l:12 000 l:5880 The condition factor (CÐ of trout was calculated from Secchi depth (meau) (m) - 0.5 5.8 the expression: cF : Y.to' L The Pukaki and Ohau canals contain brown and rainbow where V/ was weight in grams and L was fork length in trout as well a few laud-locked quiunat salmon millimetres. @loomberg et al. 1983) and sockeye salmon (L. J. Hawke, MAF Fisheries, pers. comm.). Aquatic To assess age and growth, scales were collected from a macrophytes (Myri o p hy Il um and P o t attn g et o n species) sample of trout netted in the Pukaki and Ohau canals. grow in small beds in both canals but are more common Scales were taken from between the dorsal fin and in the Ohau. Canal bank vegetation is comprised of lateral line, dry mounted between glass microscope mixed grasses aud tussocks planted by the Ministry of slides, and examined with a Nikon micro-projector (50x Works and Development. magnification). Measurements were made from the focus to each annulus and to the edge ofthe scale along the anterior axis of the scale. Where possible, five 3. METHODS scales from e¿ch trout were examined and their meåsurements averaged. The readability of each scale was rated on a scale from I (unreadable) to 5 (very easy Fish were sampled at sites on the Pukaki and Ohau to read). Scales with a readability of less than 3 canals using single-ended fyke nets aud a seine net. (readable) were disregarded because they were Fyke uets with a 30-mm mesh were set parallel to the considered to be unreliable for age and growth analysis. canal bank, in water about l-2 m deep, at five It was assumed that a single annulus was laid down equidistant sites on each canal (Fig. l). The net each winter (i.e., an age I fish had one an-nulus, aû age opening faced downstream and its lead-in was angled at 2 fish had two annuli etc.). approximately 45 degrees towards the canal bank. Fyke nets were operated almost continuously and were Iængth at age was back-calculated from scales using the cleared at least every five days from June 1983 to June following formula (Tesch 1968): 1984. I-."-c : S./S(l-c) where Lo : leng;th of trout when annulus age n was Seine netting was carried out at approximately two completed; c : correction factor for allometric growth monthly intervals between 14 June 1983 and I June which is equal to y intercept of the regression line of 1984. A SO-m-long, 35-mm-mesh net, with a 4-m-deep trout lenglh and scale radius (brown trout: c : 24-6 cod eud, was set adjacent to each fyke net site in the (mm), r :0.97; rainbow trout: c :24.5 (mm), r : Pukaki and Ohau canals, in flows ranging from 4O m3/s 0.98) (S. Bloomberg pers. comm.); So : radius from to l@ m3/s. The net was set from a jet boat and scale focus to completed an¡ulus n; S : scale radius; dragged downstream for between 30 m and I2O m I : Ienglh of fish when the scale was obtaiued. before being beached. The area of canal bed netted during e¿ch set was estimated by multiplying the A few trout were damaged in the nets or caught by distance. that the net was dragged downstream by anglers. These fish were kept for stomach coutetrt 17.5 m, which was the me¿u width covered by the net. analysis. Stomachs ,were removed and dissected aud Seine netting was carried out at night to ensure that the their fullness assessed on a scale from 0 (empty) to 10 incidence of net avoidance by trout ì¡/as similar iu both (distended). Stomach contents were identified at least canals. to their taxonomic order and counted. Each type of

Freshwater Fisheries Centre food was assigned points according to the percentage of 4.2 Lbundance and Distribution the stomach contents that it represented by weight. The number of trout in the Pukaki and Ohau canals was The Ohau Canal was drift dived for a distauce of 6.2 estimated from seine uet catch rates (fable 3), and km on 21 February 1984. The dive was conducted in resulted in density estimates of 13 trouVhætarc (or 92 tåree sections of equal length in the upper, middle, aud trout/km) in the Pukaki Canal and 15 trouUhectare (or lower reaches of the canal. Four SCUBA divers drifted 67 trout/km) in the Ohau Canal. However, these the deep water in the middle of the canal, while three estimates are minimal because they are based on the snorkel divers drifred the canal margins. Trout assumption that all trout in the area swept by the net observed by the divers were counted, identified to were captured. The number of trout that escaped from species, and their size recorded as small (<200 mm in the net is unklown, although results of a fish salvage length), medium (200-400 mm), or large ()4OO mm). operation in the Ohau Canal in 1989, where an averzlge The Pukaki Canal was not drift dived because of its of 350 trout/km were uetted, suggested that it could high turbidity. have been high (James l99O).

Drift dive counts were not used to estimate numbers of 4. BROWN AND RAINBOW TROUT trout in the Ohau Canal because r¡/ater clarity was limited during the dive (secchi depth : 3.8 m) due to recent flooding in the upper catchment. Although the 4,L Species Composition secchi depth reading 'was greater than the minimum recommended by Teirney and Jowett (1990) for drift Fyke and seine net catches showed that brown trout diving in slow flowing rivers, there were not enough outnumbered rainbow trout in both the Pukaki and Ohau divers to effectively cover the whole width of the canal. canals (fables 2 and 3). Species composition of net catches did not differ greatly between canals or netting Fyke and seine net catch rates did not differ greatly methods. Composition ranged ftom 69To brown trout between sites, which suggests that trout were evenly canals (Tables in seine net catches in the Ohau Canal to 88 % brown distributed along the length of both 2 trout in fyke net catches in the Pukaki and Ohau canals. aud 3). This result was not unexpected because the physical Species composition from drift dive counts (Table 4) canals have extremely uniform and biological was very similar to that from fyke and seine net characteristics (Fig. 2). catches, although divers could not positively identify 42 trout. Drift divers counted higher numbers of trout in the middle of the canal than at the sides. However, the

TABLE 2. Fyke net catches in the Pukaki and Ohau canals, June 1983 to June 1984.

Trout Catch comp. Per Jun Jul Aug Sep Oct Nov Dec Jan Feb Mar Apr May Jun Total % day

Pukaki Canal

Fyke net days 56 80 52 26 55 r80 150 145 t32 r55 142 155 90 r 618 Brown trout 20 l0 3225635 36 2093 115 88 0.07 Rainbow trout 1) 101000 00 212 16 tz 0.01 Longfinned eel 00 109918 I 10 050 M - 0.03

Ohau Canal

Fyke net days 365 79 105 tL2 130 50 30 140 155 t32 155 90 1246 Brown trout 26 l5 11 1362 t2 12 49 285 88 0.07 Rainbow trout 23 20 3 000 00 10 tt2 12 0.01 Longfinned eel 00 00 0 041 1l 20 09 - 0.0i

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TABLE 3. Seine net catches in the Pukaki and Ohau cauals, June 1983 to May 1984.

Trout comp. Jun Jul Aug Sep Oct Nov Dec Jan Feb Mar APr M"y Jun Total (%)

Putski Canal

Area netted 4.9 6.2 1.2 9.9 5.2 6.5 6.4 40.3 (100O m2) Brown trout 1083 )- 4- 9- 4 4l 79 Rainbow trout 151 1- 0- 1- 2 l1 2l

Ohau Canal

A¡ea netted 0.6 6.5 7.6 7.0 9.4 6.8 4.8 42.7 (1000 m2) Brown trout 0545 T3 11 7 45 69 Rainbow trout t217 4 5- 0 20 3t

TABLE 4. Numbers and size of brown and rainbow trout observed by divers in three sections of the Ohau Canal on 21 February 1984 (small (200 mm, medium 200-4AO mm, large >400 mm).

Brown trout Rainbow trout Unidentified trout small medium large small medium large small medium large

Upper 2tl 1 I 0 0 I 6l Middle 65r2 0 6 I 4 74 L¡wer 4223 4 4 I I 153

Totals t2 38 t6 t0 28

% identiñeÅ 80 zo

direct correlation between flow volume and fyke net nets, or by anglers, in I¿kes Ruataniwha or Benmore catch rates suggests that brown and rainbow trout (Freshwater Fisheries Centre unpublished data). moved to the sides of the canals at times of high flow (Fig. 3). Only 12 tagged trout were recaptured in this study (Iable 5). The distance moved and number of days between tagging and recapture averaged 3.7 km and I 1 1 4.3 Recruitment and Movements days, respectively.

The canals' trout stocks are probably maintained by fish moving downstreåm from I-akes Pukaki and Ohau. The 4.4 Lenghh, Weight, Ðd Condition Factor compacted canal bed is unsuitable for spawning, and high water velocities at the control gates prevetrt trout The mean lengh of trout did not differ significantly from moving upstream into L¿kes Pukaki and Ohau. between species, canals or netting methods (Table 6) Downstream movement is possible, but none of the 208 (ANOVA, F : 1.31, df : 71333, P <0.01). The trout tagged in the canals were recaptured in fyke or gill length range of brown trout \^/as gre:iter than for

Frqshwater Fisheries Centre 10

Ohou Conol Copocity '. tZO ,rllt (o)

ó3 5m (o"eroge)

Pukoki Conol Copocity : 41O m3fs (b)

8O.am (orerogc) Woter depth to l m filter þ------2 lining|- I . . R\_ ,ttm- ,¿1fl o o

2.5 4 rÇ oaoaoa o

FIGtlR.jE 2. Cross section of the Pukaki and Ohau canals. (From Ministry of Works and Development.) rainbow trout (Fig. 4). Lengths of brown and rainbow length at age data (Table 9). Sixty-two percent of trout trout observed by drift divers were similar to those of were estimated to be 2 or 3 years of age,22% were netted trout (fable 7). aged, 4 or 5 years, and 9To were aged 6 to 10 years. The percentage of trout aged I year (7%) was Brown trout averaged 430 g in weight and had a meao comparatively low, possibly because many juveniles condition factor of 102. Rainbow trout weighed slightly reared in upstream lakes and rivers before moving into less (mean weight : 375 g), but had a higher meån the canals (see Section 4.3). In addition, smaller condition factor (mean CF : 108). The condition juveniles were able to escape through the mesh of fke factor of both species was inversely related to fork and seine nets. leàgth and did not differ greâtly between se¿sons (table 8). Growth rates of brown aud rainbow trout were determined from information on recaPtured trout (fable 5) and mean back-calculated length at age data 4.5 Age and Growth (Iable 9). Growth râtes based on back-calculated leugth at age were comparatively fast for the first two The age composition of trout in the canals was years of life and then declined gradually in subsequent estimated by combining information from length years. Mean annual growth increments for brown trout frequency histograms (Fig. a) and mean back-calculated were 1@ mm and 125 mm for ages one and two years,

Freshrvater Fisheries Centre 11

Pukoki Conol conol rto. (m%) ¿00

100

200

r00

a ¡l ¿l \ :on \ o \ !

ru L--- 'r-a?- --È- \- -'J o I ONDJ ' Month )o

o Ohou Conol tu

c f t o- u'J--

..c o (J

o.2

MAM)

FIGLIRE 3. Correlation between fyke net catch rate and flou/ volume in the Pukaki and Ohau canals.

tr'reshwater Fisheries C-entre t2

TABLE 5. Details of tagged trout which were recaptured in nets or by anglers.

Condition I-ocationf Date Days at Length (mm) Weight (g) factor recap. Species release recapture released liberty rel. recap. rel. recåp. rel.

:F Brown trout P5 o5 Jun 1983 t52 378 550 'ß t02 o5 o4 Jul 1983 r32 507 510 1220 1250 94 94 +394 *681 *111 o3 o5 Jul 1983 r93 365 588 r2l *360 *681 *146 PI o? Aug 1983 55 371 520 toz o5 P5 Sep 1983 49 510 510 t295 1250 98 94 '77 o1 o5 Sep 1983 56 450 447 7æ 748 84 o3 n. Jan 1984 91 322 3r8 300 250 90 78 115 81 P5 P3 Feb 1984 t3 408 405 780 540 o4 02 Apr 1984 22 330 330 410 330 tr4 92 P4 P4 May 1984 7 570 570 1560 1560 80 80

+470 *975 *94 Rainbow trout o5 P4 Jul 1983 560 283 270 119 P5 P5 Jun 1983 0 307 307 220 220 76 76 t: refer to Figure I for location of sites. *: length or weight at recapture not validated. ?- exact location unknown.

TABLE 6. Mean length, weight, and conditiou factor of brown (BT) and rainbow (RT) trout caught in fyke and seine nets in the Pukaki and Ohau canals.

Number Mean Mean Condition of trout length t weight * factor Canal Net Species netted S.D. (mm) s.D.(e) + s.D.

Pukaki Fyke BT u5 341 + 122 115 503 + 442 LT4 99+15 RT 16 287 + ll5 16 322 t 248 16 106 + 28 Seine BT 41 288 + 126 39 Q7 + 644 39 108 t 15 RT ll 266 + 11.3 ll 338 + 415 l1 109 + 16

Ohau Fyke BT 85 320 + 193 84 408 t 429 81 toz + 2l RT T2 313 + 125 t2 502 + 670 T2 tll !2 Seine BT 45 293 + 64 44 302 + 2t0 44 102+9 RT 20 310 + 66 20 363 + 188 20 lll t t3

mm but only 84 mm, 73 mm, and 63 mm for ages three to rainbow trout which increased from 283 mm to 470 five years, respectively. Growth rates based on back- in length, and270 g to 975 g in weight, after 560 days calculated length at age probably included growth which at liberry. had occurred in upstream lakes and rivers (see Section 4.3) and may not be representative of trout in the canal. 4.6 Diet Growth rates of tagged trout were generally very slow and many trout actually lost weight between tagging and Analysis of stomach contents showed that trout in the recapture. The fastest growth rate was shown by a canals fed extensively on winged terrestrial insects in

Freshwater Fisheries Centre t3

Brown trout- Pukoki Conol - Fyke (n=rrz) to

20 Brown lrout Pukoki Conol Seine (n=¡c) t5 - -

Brown trout Ohou Conol Fyke (n= a¡) t0 - -

U c) 0 ql o ]t- 20 às Brown troul Ohou Conol Seine (n=ra) l5 - -

t5 Roinbow Conol - bolh methods ¡o (n=zz)

t5 Roinbow trout - Ohou Conol - both methods to (n=rz)

o JUU ¿OO 500 óOO lOO ( Length .- )

FIGURE 4. l,ength frequency distribution of brown and rainbow trout caught by fyke and seine nets i¡ the Pukaki and Ohau canals.

Freshwater Fisheries Centre t4

^f 7, Size composition of brown and raiubow TABLE 9. Mean back-c¿lculated length at age for ^BLEtrout in the Ohau Canal based on fyke and seine trout netted in the Pukaki and Ohau canals. net c¿tches and drift-dive counts.

Mean Number % composition Age length lncrement of <2æ zæ-ffi >ffi (years) D (mm) SD (mm) Specie.s Method trout (--) Brown trout Brown netting 130 24 60 l6 1 20 100 2t 100 divers 66 18 58 24 2 l8 225 40 t25 3 l5 309 4L 84 Rainbow netting 32 9 81 l0 4 5 382 65 15 divers t7 29 59 T2 5 ) 45 86 63 6 I 412 -33 7 I 444 32

Rainbow trout TABLE 8. Relationship betweea condition factor and I 295 7 95 length of trout in the Pukaki and Ohau canals, ) 2 t'78 t: 83 1983-84. Condition factor was predicted from the ) I 235 57 regression equation of frsh length v condition 4 I 298 63 factor. 5 6 7 Pukaki canal Ohau canal length length Species Season n 100 300 600 n 100 30O ó00

Brown Summer 28 lll 102 88 52 ll9 102 77 the canals. They were caught in fyke nets in both trout Autumn 35 l 13 100 8l 26 109 t01 90 canals and also were found hidiug under rocks at the Wìnter 50 108 t02 93 l8 tt? 106 88 wâters' edge. Longfin¡ed eel and koaro were the only Spring 43 t22 10ó 83 30 I 15 t02 E3 other native fish taken by fyke nets in the canals. Mean t56 I 13 102 86 126 I 15 103 84

Rainbow All 28 l l8 107 90 35 t25 1r2 93 Fyke net catch rates of longfinned eel showed a marked lrout s€asons seasonal variatiou, peaking in spring and summer and then declining in autumn and winter. Seasonal variation in eel catch rates is a common occutreûce, because eels the spring and summer (table l0). A wide variety of become less active and often hibernate in the winter winged terrestrial iusects were found, including manuka months (McDowall 1978). and ground beetles, bees, wasps, and tussock butterflies. Benthic invefebrates were present in most The majority of native fish in the canals are thought to of the samples, but did not rÈpresent a large percentage originate tiom spawning and rearing areas in upstreâm of the volume of stomach conterts. The lack of benthic lalces and rivers. Common bully, upland bully, and invertebrates in the stomachs examined reflected the koaro lay their eggs on rocks and other hard substrates very poor beuthic invertebrate fauna of the Pukaki and aud so can probably spawn successfully in the canals. Ohau cauals (pers. obs.). Juveuile trout and small However, common bully and koaro larvae are native fishes were not found in any of the stomachs, planlfonic and are likely to be swept downstream i¡to although trout have been observed chasing small fish in l-ake Ruataniwha (see McDowall 1978 for a discussiou the Ohau Canal. of the üfe histories of native fishes).

5. NATTVE F"ISH 6. DISCUSSION

Common and upland bully appeared to be the The Pukaki and Ohau cauals contained brown and commone.st and most widespread native fish species in rainbow trout and four species of native fish: common bully, upland bully, lougfinned €1, and koaro.

Freshwater Fisheries Centre 15

TABLE 10. Diet of trout in the Pukaki and Ohau canals.

% of food in Origin of Common Scientific Life Probable feeding stomachs by volume prey item name name stage location of trout Brown Rainbow

Terrestrial beetle Scarabaeidae adult water surface 44 fly Diptera adult water surface 5 butterfly I-epidoptera adult water surface <1

Aquatic beetle Elmidae adult water column 5 caddist'ly Trichoptera adult water surtàce <1 caddisfly Hudsonemn amabilß larvae water column or canal bed 36 caddisfly Olingaferedayi larvae water column or canal bed <1 mayfly Deleatidium sp. larvae water column or canal bed 5 snail Potam.opyrgus adult canal bed 6 99 antipodarum

Number of stomachs examined l0

Mean stomach fullness (%) 36 90

Predictably, the species composition of fish in the Brown and rainbow trout in the canals were smaller canals was very similar to that found upstream in I-akes than in most other lakes and rivers in the upper Waitaki Pukaki and Ohau fliling 19'79). Species composition of catchment with the exception of Lake Middleton (Mace fish in the canals also was similar to that recorded in Ward, Nelson-Marlborough Fish and Game Council, the Tekapo River and Lake Benmore, but differed from pers. comm.). The condition factor and growth rate of most other upper V/aitaki lakes and rivers, which trout also were comparatively low, and stomach support a higher percentage of rainbow trout contents analysis suggested that this was due to a lack (Table 11). of tbod in the canals. Benthic invertebrates and small t-rsh were scarce and winged terrestrial insects were The estimated number of trout per kilometre in the abundant only in spring and summer. The lack of food canals was considerably higher than that recorded in the in the canals can be attributed lar-eely to the absence of residual Ohau River, which has a mean flow of only riffles and to the oligotrophic nature of upstream lakes. 0.4 m3/s (Trought 1984). Numbers of trout in the Rift'les are the main areas of benthic invertebrate unmodified Ohau River were not assessed before it was production in tìowing waters and their absence almost dewatered in 1982, but would certainly have been much certainly limits benthic invertebrate numbers in the higher than in the residual Ohau. Estimated numbers of canals. trout per kilometre in the canals were slightly higher than in the lower reaches of the Ahuriri River, but were The poor condition and slow growth of trout also can be less than in the lower sections of the Tekapo River. attributed to a lack of cover in the canals, as trout in Compared to rivers drift dived in other parts of Nerv straightened artihcial chan¡els spend a considerable Zealard, the canals supported low to medium numbers amount of energy swimming, just to maintain their of trout per kilometre (Jowelt and Hicks 1985). position in the current (Tesch and Albrecht 1961, cited in Hynes 1970). The amount of cover could easily be It is not possible to compare trout abundance in the increased by placing rocks and boulders on the canal canals with that in the upper Waitaki lakes because data bed and planting suitable species of aquatic macrophytes are limited to one biomass estimate of 2.9 g/m2 for in the canals. Aquatic macrophytes already present in I-ake Alexandrina (Mark Webb, South Canterbury Fish the canals are used extensively by trout for cover and and Game Council, pers. comm.). However, the provide habitat for benthic invertebrates such as snails. majority of lakes in the region are deep and oligotrophic Planting riparian vegetation also would increase the (Stout 1975) and probably support much lower densities amount of cover, as well as enhancing the scenic value of trout than either Lake A-lexandrina or the canals. of the cauals. However, these measures are

Freshwater Fisheries Centre t6

TABLE 11. Comparison of trout stocks in the Pukaki and Ohau canals with other waters in the upper Waitaki catchment.

Canals Rivers l¡kes Benmore Pukaki Ohau Ohaur Tekapo Ahuriri Alexandri¡u Pukaki Ohau Ruataniwha Haldon Ahuriri

Species composition (% rainbow trout) Angling 28 28 3141 37-51 36 75 0 64 36 3ó Drifl diving 20 - 39-62 4'7-64 Netting 21 3l 86 zo 20-ó0 45 9-59 9{0 Spawning run - 3-26 80-98 l8 3-26

Deosity and biomass (species combined) No./km (>200 mm) +75 '53 - 101- 126 46-55 j26- kg/km (all fish) +42 -58 2t-30 ?o gim: (all fish) . J.J 1.0-1.4

Brown trout

Mean lengh (mm) Netting 327 311 430 338 296 300 327 326 Trapping - 454440 540 413 Angling 400 400 461 +521 472 562 - 162 489 410

Mean weight (g) Netting 478 371 I 033 ,ol 308 4t0 410 434 o5') Trapping - 1072-1045 2295 Angling 700 700 + I 181 ró00-1800 +t220 2375 + 1144 1356 800

Mean CF 101 103 - 104-122 r24 t1'1 109 t2'7 lll lll

Rainbow Trout

Mean length (mm) Nening 2'78 311 335 282 336 298 307 28'7 Trapping - 488-505 541 - 446 Angling 438 432 .178 + 471 426 526 500 +71 390

Mean weight G) Netting 329 4r5 451 283 500 381 400 316 Trapping - t3'73 2059 tl27 Angling 900 900 r387 1000-1600 982 I 894 + 1587 t349 800

Mean CF t0'l lll - 109-120 t20 I t'l 131 122 125 122

Reference sources: Bloomberg et at. 1983i Graynoth and Skryznski 1973; Hayes 1986: Jellyman et al. 1982; Jowen 1978: Jowett and Hicks I985: lr{AF Fisheries unpublished data; Moore et al. î.d.i Page 1986; Teirney and Jowett 1990; MarkVr'ebb' South Canterbury Fish and Game Council, pÈrs. coÍirn. | : unmodified Ohau River. - : no data. + : density estimatè based on seine net catch rates and not drift-dive counts. CF : condition factor. * : derived from lengrh or weight using CF : I 16 for brown trout, and 127 for minbow trout.

unacceptable to Electricorp because they would reduce Ohau River fishery. The canals support smaller, Poorer the canals' hydrological efficiency and cause erosion of conditioned trout than the Ohau River, and have lower the banks. values in terms of scenery and solitude $ermey et aI. 1982a). They also are unsuitable for other recreåtional The results of this study suggest that the Pukaki and activities, such as camping and picnicking (boating and Ohau canals are unlikely to be highly rated by anglers ratting on the canals are prohibited) ' However, the loss and do not compensate for the loss of the highly valued of the Ohau River was partly offset by the marked

Freshwater Fisheries Centre t7 improvement in the Tekapo River fishery which James, G.D. 1990. Ohau Canal trout abundance. followed diversion of water into the Tekapo Canal in Freshwater Catch No. 42: l0-11. 1977. T\,e Tekapo River now supports extremely good stocks of brown and rainbow trout and allows a wider Jellyman, D.J., Davis, S.F., Wing, S.J., and Teirney, range of angling methods than the Ohau River. The L.D. 1982. Fish stocks of the Ahuriri River Tekapo River also has high values, in terms of scenery system. N.Z. Ministry of Agriculture and and solitude (Teirney et al. L982b) although occasional Fßheries, Fßheries Environrnental Report No. 26. spillway releases from Lake Tekapo can greatly reduce 84 p. angling quality. Jowett, I.G. 1978. Upper Waitaki power development and fisheries. Internal report, Power Division, 7. ACKNOWLEDGEMENTS Ministry of Works and Development. 18 p, plus tìgs.

We wish to thank Kevin Kirkwood, Ian Mackenzie, Jowett, I., and Hicks, B. 1985. Estimatiou of Greg Trought and other MAF Fisheries consultants and comparative trout abundance in New Zealand temporary staff who assisted in the field programme, rivers by drift diving. Freshwater Catch No. 28: together with Freshwater Fisheries Centre staff tbr 8- 10. commenting on the manuscript. We would also like to thank New Zealand Electricity Division of the Ministry McDowall, R.M. 1978. "New Zealand Freshwater of Energy (now Electricorp) for funding this work. Fishes. A Guide and Natural History. " Heinemann Educational Books (N.Z'.) Ltd., Auckland. 230 p. 8. LITERATIIRE CITED Moore, E., Cunningham, 8.T., L-ane, E.D., and Lewall, E.F. n.d. Spawning survey of I-ake Bloomberg, S., Stancliff, 4.G., and Thornton, B.K. Alexandrina and adjacent waters. N.Z. Marine 1983. Angling in the upper Waitaki catchment Department, Freshwater Fisheries Advísory 1980/81 season. N.Z. Ministry of Agriculture and Service Investigation Repon No. 40. Unpaged. Fßheries , Fisheries Environmental Report No. 18, t7 p. Page, M.J. 1986. Distribution, feeding and growth of brown and rainbow trout in Lake Alexandrina. Graynoth, E. 1984. Effects of hydroelectric M.Sc. thesis, University of Canterbury. l4l p. development on the fisheries of the Wâitaki River, New Zealand.pp.427-436. In: Lillehammer, 4., Stout, V.M. 1975. Canterbury, Nelson, and Vy'estland lakes. pp. ll0-122. JoIIy, V.H. and Brown, and Saltveit, S.J. (Eds.) "Regulated Rivers. " In: Universitetsforlaget AS, Oslo. 540 p. M.A. (Eds.). "New Zealand l-akes." Auckland University Press. 388 p. Graynoth, E., and Skrzynski, W. 1973. The South Canterbury trout and salmon tìshery. N.Z. Teirney, L.D., and Jowett, LG. 1990. Trout abundance in New Zealarrd An assessment Minßtry of Agricubure and Fisheríes, Físlteries rivers: Technical Repon No. 93. 47 p. by drift divin-s. N.Z. Freshwarer Fisheries Report No. 18. 3l p. Hayes, J.W. 1986. Fish and fisheries values of Lake Alexaudrina and their sensitivity to eutrophication. Teirney, L.D., Richardson, J., and Unwin, M.J. value Waitaki Valley N.Z. Minßtry of Agricuhure snd Fisheries, 1982a. The relative of preliminary Fisheries Environm¿ntal Reporr No. 63. 45 p. rivers to Waitaki Valley anglers: A report. N.Z. Ministry of Agricuhure and Hynes, H.B.N. 1970. "The Ecology of Running Fisheries, Fßheries Environmental Repon No. 19. Waters." University of Toronto Press. 555 p. 46 p.

James, G.D. 1985. Modifications to regional Teirney, L.D., Richardson, J., and Unwin, M.J. waterways Part VII - the Waitaki region. 1982b. The relative value of South Canterbury Freshwater Catch No. 27: 10-14. rivers to South Canterbury anglers: A preliminary report. N.Z. Minßtr1 of Agriculture

Freshwater Fisheries Centre 18

and Fisheries , Físheries Environm¿ntal Report No. 17. 46 p.

Tesch, F.W. t968. Age and growth. pp.93-123.In: Ricker, W.E. (Ed.). "Methods for Assessment of Fish Production in Frqsh Waters." International Biological Programme Handbook No. 3. Blackwell.

Trought, G.J.T. 1984. Residual flows in the upper Ohau River. N.Z Ministry of Agrtcuhure and Fßheries, Fisheries Envìronmcntal Report No. 38. 27 p.

Wing, S.J. 1979. Fish species in the upper Waitaki lakes and rivers. N.Z. Minßtry of Agricuhure and Fisheries, Fisheries Environ¡nental Repon No. 6. 1o p.

Fræhwater Fisheries Centre