SER MV?Æ 01r1 - 4794 FISH rssN ENVIR REP 26

I FISHERIES ENVIRONMENTAL REPORT NO. 26

FISH STOCKS

AND FISHERIES OF

THE AHURIRI RIVER SYSTEM

FISHERIES RESEARCH DIVISION MINISTRY OF AGRICULTURE AND FISHERIES

CHRISTCHURCH FTSH STOCKS

AND FISHERIES OF

THE AHURIRI RIVER SYSTEM

BY

D.J. .]ELLYMAN

S. F. DAVIS

S.J. lllING

L.D. TEIRNEY

F]SHERIES ENVIRONMENTAL REPORT NO. 26

N.Z. MINISTRY OF AGRICULTURE AND FISHER]ES

CHRISTCHURCH FISHERIES ENVIRONMENTAL REPORTS Ed'i ted by: S . F. Davi s

This report is one of a series of reports issued by Fisheries Research Division on important issues related to environmental matters' They are issued under the following criteria: (1) They are informal and should not be cited without the authorrs permission.

(2) They are for timited circulation so that persons and organisations normally receiving Fisheries Research Division publications should not expect to receive copies automatically. (3) copies will be issued initially to organisations to whích the report is directlY relevant. (4) copies will be issued to other appropriate organisations on request to Fisheries Research Division, Ministry of Agricul-ture and Fisheries, Private Bag, Christchurch.

(5) These reports will be issued where a substantial report is required with a time constraint, e.g. a submission for a tribunal hearing" (6) They will also be issued as ínterim reports of on-going environ- mental studies for which year by year or intermittent reporting is advantageous. These interim reports will not preclude formal scientific publication. CONTENTS

Page

1. Introducti on 1 1.1 Obiectives of this rePort 6

?. Catchment Description 6

2.L Hydro'l ogy 7 2.2 Sediment 11 2.3 Water qual ity 11

3. Use of the Water Resource t2 3. i Irrigation 12

3 .2 Hydroe'l ectri c power generati on 13 3.3 Recreation L4

4. Me thods 16 4.L Bottom fauna 16

4 .2 El ectric f i sh'ing 16 4.3 Trout taggìng L7 4.4 Drift diving 18

4 .5 Ang'ler surveys 19 4.6 Lake Benmore studies 20

4 .7 Trappi ng 20 4.8 Spawning surveys 20 4.9 Sockeye salmon studies 22

4. 10 flati onal ang'l i ng survey 24

5. Bottom Fauna 25

6. Fi sh stocks 27

6.1 Common bully (eobio orphus cotidianus) 28 6.2 Upland bu'lly (cobionorphus brevìceps) 28 6.3 Koaro (cal-axias brevipinnis) 29 'll

Page

6.4 Common river galaxìas (cal-axias vuJgaris) 29 6.5 Longfinned eel (ensuil7a dieffenbachij) 30 6.6 Brown trout (sul*o trutta) 30 6.6.1 Juveniles 3T 6.6.2 Species proportions and distribution 31 6.6.3 Size 35

6.6.4 ltlovements 35 6.6.5 Dens'ity 36 6.6.6 Growth rate 37

?a-^------i-^- ao o. o. / Jpdwil illg JO

6.7 Rainbow trout (sul*o gairdnerii) 42

6 .7 .l Juven'i I es 42 6.7.2 Size 42

6.7 .3 Movements 43 6.7.4 Density 43 6.7 .5 Growth rate 43

6 .7 .6 Spawn i ng 43 6.8 Sockeye salmon (oncorhgnchus nerka) 44

7. Recreati onal Fi shery 45 7.I Catch rates 45

7 .2 Areas fi shed 47 7.3 0rìgìn of angl ers 47

7 .4 Val ue of the Ahuriri River fishery to anglers 49

7 .4.t Summary of pre'lìminary results 49

7 .4.2 Vi s i ti ng angl ers 50

7.4.3 Characteristics of three reaches of the 53 Ahuri ri

7 .4.4 Estimates of total usage 55

7 .4.5 National importance of the Ahuriri 57 ii'i

Page

8. Discussion 59

9. Conclusions 67

10. Summary 67

11. Further Information Required 69

12. Acknowl edgements 77

13. L'iterature Ci ted 7I

14. Append'ices I . Angler interview form. 77

II. Cl assi f icat'ion of river fi sheri es 78 of national importance. III. Factors affect'ing fish hab'itat , and B1 their relationship with di scharge.

TABLES

1. Benth'ic invertebrate samples collected on 2 Ju'ly 1979. 26

2. Range and mean density/mz of benthic invertebrates at 27 a1 I samp'l i ng s'ites durì ng l97B- 1980 '

3. Summary of trout size data from Ahuriri River angler 34 catches, L962-I982.

4. Recaptures of trout tagged in the Ahuriri River and 35 Lake Benmore.

5. Growth in length of tagged trout. 37

6. Summary of upstream trout catches at Tekapo River and 38 Mary Burn traps, I98?.

7. Spawn'ing counts in the Ahuriri River and tributaries, 39 1973-L982.

8. Ahuriri River trout catch rates, 1957-1982. 46 1V

Page

9. Home acclimatisation society of anglers interviewed 49 on the Ahuriri Rjver, I97B-I982.

10. Number of National River Angl ing Survey respondents 51 who fished the Ahuriri River.

11. Estimated number of adult angìers who visit the Ahuriri 56 River from each acclimatisatjon society distrjct.

12. Comparative information about ang'ler usage and importance 58 grades assigned to nationally 'important South Island recreational trout fishing rivers.

13. Comparat'ive ang'l'ing data for some South Island trout 64 fi sheri es .

14. Crìteria used to classify nationally 'important South 79 Island river fisheries into wilderness, scenic and recreational categories.

FIGURES

1. Ahuri ri River system.

2. Wai taki hydro-e1 ectric pov'Jer devel opment, show j ng the location of control structures and dams.

3. Dewatered Ohau River, after diversion of water to the 0hau power canal.

4. Mean monthly discharge for the Ahuriri River at South Diadem, 1964-1981. tr Ahuriri River flow duration curve. 10

6. Electric fishing and bottom fauna sampling s'ites, 15 t977 -1981..

7. Fish trap on the Ahuriri River, upstream of Avon Burn 2t confl uence.

B. Length frequencies of brown and rainbow trout sampled 32 by electric fishing, December 1 977-April T978. Page

9. Trout spawn'ing areas in the Ahuriri River system. 4t

10. The Ahuriri R'iver at Omarama Bridge, on state Highway 8. 4B

11. Percentage of v'isiting and local anglers using four 52 angl i ng methods on the Ahuri ri R'iver. 1. INTRODUCTION

The Ahuriri River is located in the southwest of the Mackenzìe Basin, rising'in the main divjde and flowing into Lake Benmore (Fig. 1). Approximately

13 km of the lower reaches were inundated when Benmore dam and power stat'ion were completed and Lake Benmore filled in December 1964, but the remainder of the catchment 'is essentially unmodified, apart from pastoral development.

In comparison, the t,'laitaki River, its catchment and tributaries have undergone large scale modifications as a result of hydro-electric development over the last 40 years (Fig. 2). The Tekapo, Pukaki and Ohau Rivers are now all subject to flow control. In fact, the lattertwohardly iustjfy use of name "r'iver", since they essentially operate as spillways for Lakes Pukaki and Qhau, which are reservoirs for water required for power generatìon throughout the Wajtaki power development scheme. The Ohau River (Fig.3) ceased to exist as a free-flowing river in 1982, with construction of a power canal and creation of Lake Ruataniwha.

The Wa'itaki River itself has three large dams and associated impoundments Benmore, Aviemore and Llaitaki. Waitaki power station was the first dam to be built on the Waitaki River. Construction began in 1928, and first power was produced'in 1935. Benmore is New Zealand's second largest power statìon, and was the second to be bu'ilt on the Wajtakj, beìng commiss'ioned in January i965. Final'ly came Aviemore, which produced its first power in 1968. An artific'ial spawning race was included downstream of the Aviemore powerhouse, to provide for trout which formerly m'igrated upstream from Lake Llajtaki to spawning grounds just above the Aviemore dam sjte. Future p'lans downstream of Lake l,rlaitaki include the option of constructing a power canal along the south bank and leav'ing a residual river for recreat'ion, fish and wildlife (Graynoth, Pierce and t'Iing 1981). 2.

^ô. ¡nr. HUXLEY

AHURIRI HOPKINS RIVER RIVER

SNOWY CREEK

EAST BRANCH OHAU RIVER

QUAIL BURN

HEN BURN RECORDER Ctny íOMARAMA LAKE BENMORE

LONGSLIP OMARAMA CREEK STREAM

FIGURE 1. Ahuriri River system. GODLEY R.

TEKAPO A

TASMAN R I HAKATARAMEA R. TEKAPO R

L.BENMORE PUKAK¡ DAM \ 1'ov¡u

OHAU B

T.RUATANIWHA BENMORE OHAU A DOBSON R / L.AVIEMORE ' o¡¡rR¡¡,tr OTEMATATA R, \ I-.WAITAKI WAITAKI DAM WAITAKI R HOPKINS R,

AHURIRI R

(,

FIGURE 2. Waitaki hydro-electric porver development, showing the location of control structures and dams. 4.

FIGURE 3. Dewatered River, after diversíon of water to the Ohau power canal . 5.

l^Jithin th'is high]y developed catchment, the Ahuriri River must be v'iewed as the last major, relat'ively unmodified tributary remaining ìn the Wajtaki region. The fishery is highly va'lued by angìers (Teirney, R'ichardson and Unwin lg82), and the river is an ìmportant spawning tributary for both brown and rainbow trout, jncluding both resident fish and fish from Lake Benmore.

The recently published draft national inventory of wild and scen'ic rivers

(N¡IASCO tg82) placed the Ahuriri River (from its source to Lake Benmore) on jts "4" Iist. This list consists of rivers which have "outstanding wi1d, scenic, recreational or other natural characteristics". The Ahuriri River was ident'ified on the basis of its recreational and biological/scientific values.

Further, the acclimatisation society movement have notified the Waitaki

Catchment Comm'ission of their intent to apply for a National Water Conservation Qrder for the Ahurirj River, under the 1981 Amendment to the Water and Sojl Conservation Act (1967). The implicat'ions of this application are unclear, sìnce no river has yet received protection under the new legislation. (Applications for the Motu River in the Bay of Plenty (national order) and Stony River in Taranaki (local order) are still beìng processed.)

The Wildlife Service of the Department of Internal Affairs have also indicated that they may apply for a National Water Conservation Order. The basis of their appl'ication would be the national importance of the Ahuriri River for black stìlt (which is probab'ly the rarest wading bjrd in the world), wryb'i1ìed plover, banded dotterel and black-fronted tern - species whjch are all endem'ic to New Zealand.

Fisheries Research D'ivision (FRD) staff init'iated exploratory surveys on the Ahuri ri Riverin 1975. However, in response to interest shown by Waìtaki Electric Power Board in the Ahuriri's potential for small hydro-electrjc

development, more detailed studies commenced in December L977. The emphasìs of FRD's research programmes in the Waitaki catchment has centred on assessment of the'impacts to fisheries of the upper LJaitaki power scheme, and developing an understanding of the fish stocks and fisheries of the lower blaitaki, to predìct 6. the fishery requirements for a residual river. Therefore, fìe1d programmes on the Ahuriri River have been conducted at a relatively low level, on an inter- mittent basi s.

1.1 0bjectives of thjs Report This report has been compiled to assist the Wa'itaki Catchment Commission in their assessment of the potent'ial impact of a proposed 4 m3/s abstraction of water, and as a background fisheries statement for a proposed water management plan. The objective of the report is to outline FRD's current state of knowledge of the fìsh stocks and fisheries of the Ahuriri River system, and to describe the recreat'ional fishery in both a regional and national context. The data have been summarised at short notice and the report does not specifical'ly address the questions of the 'impacts on fisheries of further water abstractjon, s'ince none of the fjeld work was designed to provide such informatjon.

Publication of this report should not be taken to mean that FRD considers satisfactory ìnformat'ion is available to answer these questions. Further studies are necessary to improve understandìng of the Ahuriri fishery resources, and

FRD has initiated a summer field programme to provide some information on fish populations in the river reach below the proposed abstraction site. However, w'ith prior commitments of staff and resources, the work that can be undertaken in the time available is limited.

This report summarises informatjon available on the Ahuriri fish resources, discusses the limitations of the data and recommends studies which should be done before further water is allocated from this valuable resource.

2. CATCHI4ENT DESCRIPTION

The Ahuriri catchment is high; the river rises on the slopes of Mt Huxley

(elevation 2500 m), but there are no glaciers in the headwaters. The gradient of the river bed is relatively steep, falling 1380 m over its 76 km iength' to an altitude of 365 m at Lake Benmore. in the upper reaches, the river flows 7. through a wide va'lley, and is generaìly confined to a single channel. There is a short rocky gorge with a low waterfall in the m'iddle reaches at South Diadem, where Ministry of Works and Development (Ml,rlD) operate a water level recorder (FÍg. 1). Below th'is gorge the river opens out into a broad, braided, shingle f l oodpl a'i n.

Total catchment area is 1670 km2, of whìch 557 km2 lie above South Diadem gorge. Above the gorge the catchment comprises typìca1 glaciaì landforms (0'Connor L976), while downstream the river flows through an alluvial plain, bounded by co1 I uv'ial fans .

nrioinatinc as it does in the main divide, the rìver flows through a wide rajnfall gradient. Precip'itation in excess of 5000 mm per annum occurs in the headwaters, decreasing to about 500 mm at Omarama. Gabjtes, Porter and Partners (L1BZ) noted that "a key characterist'ic of cljmate in the upper Waitaki is wide annual va¡iation". Generalìy, precipitatìon js sìightly lower in winter, with most falling as snow at altitudes over 1000 m.

Vegetation also varies through the catchment. I'lative beech forests occur in the upper reaches, giving way to grassland and areas of matagouri scrub lower downstream. Since the arrival of man, burning, overgrazing and rabbit infestation have all played a part in altering the landscape. In the lower reaches, willows (sut¡* spp.) are the dominant vegetation in close proximìty to the river, along with some'lupins. hlithin the river itself, there is occasional macrophyte growth in backwater areas.

2.I Hydrology Ministry of Works and Development (llhlD) have operated two water level recorders at different sites on the Ahuriri River (M'inistry of Works and Development 1980). The first was at Benmore, before the lake level was rajsed, and operated from 22.3.46 - 29.li.64, with no records during the period 19.12.46 - 14.10.49. The second site at South Diadem (Fig. 1) has operated continuously since 26.8.63. B.

Mean annual discharge at the Benmore site during the period 1949-1965 was 30.0 m3ls (Ministry of Works and Development 1980), while at South Diadem during 1963-1981 mean flow was 22.7 n3/s (Ministry of Works and Development 19Bi).

Mean monthly discharges for the Ahuriri River at South Diadem are shown in

Fìgure 4.

The Ahuriri River's flow pattern is similar to other snow and ice-fed rivers which used to flow in the upper l.laitaki (e.g.Pukak'i and Ohau Rivers), although these ¡ivers were lake-regulated. (Both rivers have been modified by hydro- electric developments and now operate only as flood-spi'll channels from the storage lakes.) Essent'ia'lìy, the seasonal flow pattern consists of a winter low flow period (prec'ipitation is "locked up" as snow and ice in the headwaters), and a spring-early summer peak f'low period (the thaw). The Ahuriri also exhibits a period of reduced flows in March-April (Gabites, Porter and Partners re82).

A flow duratjon curve, based on MlrJD records from the South Diadem recorder site, is shown in Figure 5. The curve shows that discharge exceeds 9 m3/s for 90% of the time. The lowest flow recorded during the period 1964 - 1982 was 6.3 m3/s'in July 1977. However, the lowest summer flow (October-March) was 7.1 m3/s in March 1978.

Below Diadem Gorge, three major tributaries enter the Ahuriri - Longslip Creek,Omarama Stream and Quail Burn (Fig. 1). Seasonal fìow patterns for Omarama Stream and Quail Burn were ìllustrated in Gabites, Porter and Partners (tgBZ) (Fig.44 C, p. I07). In both tributaries, peak flows occur during winter, and there is a marked summer low flow period from January-April. Thus these tributaries do not sìgnificantly increase base flow in the Ahuriri River during summer.

Downstream of the Clay Cliffs (FìS. 1), the river divides into three main braìds. The northern, or main stem carries about 65% of the flow, while the other two braids are approximate'ly equal in size (Robinson and Hall 1982). 40

35

(f 30 U1 C) - 25 F c) m 20

=(¡) 15 U'

10

5

0 FEB IqAR APR MAY JUN JUL SEP 0cT NOV

FIGURE 4. Mean monthly djscharge for the Ahuriri River at South Diadem, 1964 - 1981. (o 10.

50

40

30

20

|t'l

(f) F

UJ(5 É. IU (-)- a./) ã

10 20 30 40 50 60 70 80 90

PERCENT OF TIME EQUALLED OR EXCEEDED

FIGURE 5. Ahuriri River flow duration curve. 11.

gmarama Stream has been the subject of both river control works and swamp dra.inage. Two attempts have been made to drain Twaddles Swamp (above Tara Hills) using a dragline, first'ly in the mid-1950's and more recently about 1970. These works still result in water discolouration and siltat'ion during high f'lows. in Several smal I groynes and rock protection works have al so been constructed the vicìnìty of 0marama and the road bridges during the last 10 years.

2.2 Sedi ment Sediment levels in the Ahuriri,Ohau and Mary Burn rivers were assessed using data from MWD's TIDEDA system. Mean sedjment loads were 5 mg/l for the Mary Burn, 7 mg/1 for the Ohau and 14 ng/1 for the Ahuriri. The values for the ghau and Mary Burn are except'ional'ly low, and reflect their respect'ive origins; the Mary Burn is spring-fed, while the Ohau is lake-fed. The Ahurirj, be'ing snow- and rain-fed, carries more sediment than e'ither of these two rivers, but the concentratjons are still very 1ow. Guideljnes relating sediment loadings to the quality of river fisheries (European Inland Fìsheries Advisory Commission 1964) suggest that concentrations up to 25 ng/1 have no effect on fisheries, while concentrat'ions up to 80 mg/l support moderate to good fisheries. Sediment distribution curves show that the Ahuriri River camies less than 25 mg/1 for

90% of the time, and carries over B0 mg/l for 1.5% of the time'

2.3 Water Qual i tY Water chemistry'in the Ahuriri catchment has not been thoroughly'investigated, but jn general water qua'lity in this area is considered to be hìgh (O'Connor 1976). A low population density has meant that there has been little'impact on natural water qualìty, but it is poss'ible that the river reach downstream

of 0marama could become an area of concern in the future, as a result of effluent d'ischarge and run-off from the town.

There are lìmited data available on water temperatures. Average temperatures recorded during flow gaug'ings at Mt¡lD's South Djadem site were presented by Jowett (1978) and ranged from 14"C in January and February to 4oC in July and 12.

August. FRD staff recorded spot water temperatures during electric fishing surveys. The highest temperature recorded in the mainstem was 18.5"C at Chain Hjlls on 7 April 1978. Further information is required, however, partìcu1arly on Summer water temperatures in the lower reaches of the river"

3. USE OF THE WATER RESOURCE

3. 1 Irri gqt.þn At the present time, water ìs abstracted from the Ahuriri Rjver for purposes irrigation of stock and domestic supply, ìrrìgation and grave'l washing. current rìghts are for diversion of up to 2.73 m3/s" Some of this water is diverted into gmarama Stream (up to 0.58 m3/s), and gaug'ings by the Waitaki Catchment

Commission show that in low flow periods, up to 75% of the flow in the stream below Tara H'ills is from the Ahuriri diversion (Robinson and Hall 1982).

In recent years, the Ahurjri River has been investigated for both hydro- 'identified electrjc and irrigation potentia'1. Irrigation sites have been by the 1¡ajtaki Regional Water Board (1975, L977), Kerr (1979), Gabites, Porter and partners (t982) and Robinson and Hall (i982). Approximately 13 740 ha of land in the Ahuriri catchment has been identified as ìrrigable. 0f this area' over

60% (B 500 ha) has soils of low or marginaì suìtabi'lìty forirrigation (Waitaki Regional l,{ater Board 1977). Further, the potential irrìgatìon demand exceeds the water resource available for irrigation from the Ahurirì River,Omarama Stream and Quail Burn.

Tara Hills (a Ministry of Agriculture and Fisheries' agricultural research station) began irrigat'ing'in the 1960's by abstracting water from 0marama Stream. Currently, a joint appìicatjon by Tara Hills, Killermont Run Ltd,Omarama Station Ltd and Twjn Peaks has been lodged with the Waitaki Catchment Commission to abstract up to 4 n3/s from the Ahuriri River. hJater is requ'ired to irrigate

3000 ha in the area known as Red Flat, and supolement the water supply to Tara Hjlls by discharging additional water (up to 250 l/s) into Omarama Stream. 13.

The Wajtaki Catchment Commission has deferred processing th'is water rìght app'l i cat'ion unti I Apri I 1983 . A1 though a draft water al I ocati on pl an for the

Mackenzie-Qmarama district was prepared by the Commiss'ion jn 1975, it was not formally adopted. Thus, at present, there is no management plan for the Ahuriri

R'iver, and no bas i s for water al I ocati on .

Invest'igatìons by Ml,lD irrigation engineers suggest that it may not be necessary to abstract water from the Ahuriri River to'irrigate Red Flat. A commun'ity'irrigation scheme us'ing water drawn from the Lake Ohau outlet control works could provide water to about 2500 ha'in the basin between the Ohau and Ahu¡iri Rivers (Fig. 2) and 1500 ha in the Omarama-Red Flat area (Reid 1982).

Reid QgAZ) estimated that about 6 m3/s of water would be required to deliver

100 mm depth of water at 10 day intervals during the driest part of the season. All th'is water could be provided from the upper Waitak'i power scheme. In 1968' provisjon was made for allocatjon of up to 14 m3/s for irrigation from upper

Wa1taki waters designated to be of nat'ional 'importance (Fork Stream, Lakes Tekapo' pukaki and Ohau and the waters flowing from these lakes into Lake Benmore) (Gabites Porter and Partners 1982).

To date, irrigation investigations have considered only the potent'ia1 for increasing agnicultural production on suitable soil types. No economic evaluat'ions have been reported, the water requirements of fish, wildlife and recreation, and the value of the Ahuriri as a recreational resource have not been taken into account as competing water users.

3.? Hydroelectric power generation Recent studies by Royds, Sutherland and Mcleay (l9BZ) have identified 19 potential small hydro-electric schemes in the Waitaki Electric Power Board's area. Five of these are based on water from the Ahuriri; the Ahuriri-Lake 0hau, Ahuri¡i-Hen Burn (two powerhouses) and Ahuriri-Avon Burn (also two powerhouses) schemes. The most economic scheme is said to involve divers'ion of the Ahuriri from a s'ite upstream of Diadem Gorge through a canal to a power station dischargìng 'into Lake Ohau (ea¡ites, Porter and Partners 1982). This proposal conflicts wìth t4.

.irrigation, f.isheries, wjldlife and recreational interests in the lower reaches of the Ahurìri, as most of the water would be djverted from the catchment, ìeav'ing only a residual river downstream of the diversion'

The two other schemes also involve divers'ion canals - one to the Hen Burn, the other to Avon Burn - and both include two power houses. Although the Hen

Burn scheme would generate slightly more power than the Ahuriri-Ohau d'iversion, the latter has the advantage that the water could also pass through Ohau A' B and C power statjons, thus prov'id'ing additional generation capacity. Gabites' porter and partners oggz) noted that the economics of the proposed power schemes on the Ahuriri have been assessed "without consideration of the incompatib'le and competing uses of water for irrigation, recreation and fisheries." They also po1nted out that until a water allocation pìan for the Ahuriri River has been decided, it will not be known how much water will be available for either ìrr.igation or power generation "as fish'ing and recreational interests will make justifiable claims for the water to be reta'ined in the river"'

3.3 Recreation The Ahurirì River catchment is used for angf ing, canoeing, jet-boat'ing' rafting, swimming, Þicnicking, camping, tramping and hunt'ing. Egarr and Egarr (1981) rated the river's recreational value as "high" and its scenic value as "pìcturesguê", and noted that "because it is the only maior river of the Upper l¡Jaitaki catchment left in a free flowing state, it receives a great deal of

recreational use. "

The river js extremely popular for canoes and kayaks and is used and valued for slalom competjtion canoeing (Egarr and Egam 1981). The gorge and waterfall area is important for canoe training, and wi'lf increase in value when the Clutha R.iver's "Cromwell Gap" ìs flooded by the C'lyde dam. Jet boaters can gain access from Lake Benmore through to South Diadem gorge, and can boat the upper reaches at high flows by launching at B'irchwood Stat'ion (Fig' 6)' js There'is a camping ground at Omarama, and the river in this area used extensively for swimming. Above the rnraterfall at South Diadem there are also a 15.

BIRCHWOOD STATION

o

¡,14 BEN AVON LAGOONS

+ TRAP SITE

LAKE BENMORE

OMARAMA STREAM

^ Electric fishjng site

^ Bottom fauna site

FIGURE 6. Electric fishing and bottom fauna sampling sites, 1977-L98L. 16.

(Egarr Egarr 1981)' number of large Pools suitable for swimming and

in The use and value of the river for angling are discussed in detail Sectjon 7 of thìs rePort.

4. METHODS

the Ahuriri Due to the discontinuous nature of fjsheries'investigat'ions of River, the range of species and sizes of fish sampled, a variety of technìques along with the has been used in FRD's studies. Each method'is described below, dates and locations where investigations have occurred.

4.1 Bottom Fauna Benthjc ìnvertebrate samples were collected from seven sites in the Ahuriri R.iver and tributaries during 1978 - 1980. At each site (F'ig. 6), five or six (waters and repl.icate samples were taken, us'ing a 0.1 m2 mod'ifjed surber sampler preserved Knapp 1961), fitted with a 0.1 mm mesh nylon net. Invertebrates were groupings in the'laboratory. in I0% formal.in and later sorted into broad taxonomìc The number of animals/m2 was calculated from the mean of the replicate samples at each site.

4.2 Electric F'ishing Both native fish and trout were sampled at fìve sites, using electric fishing

equipment (Burnet 1959), between December 7977 and February 1981' At each sampling site (Fig.6), a measured area ranging between 20-80 m2, was fished using a single electrode and two runs through the area. All fish caught were anaesthetised and ident'ified. The most common spec'ies were then measured and all fish released on site. Any trout larger than 15 cm were tagged with a 'Floy' streamer tag before release.

Physical descriptìons of the electric fjshing s'ites are as follows:

(i ) Avon Burn/TraP Si te water' This site was located on the ma'in river channel in fast, turbulent 17.

There was no riparian cover, and instream cover was provided by large cobbles which comprised much of the substrate. 0n'ly fast water along the margins of a run was sampled.

(ii ) lulainstem near Longs'lip Creek A medium-sized braid which ended in a backwater was samp'led at this site. Again there was no riparian cover, wjth instream cover provided by the medium to large cobbles which made up the substrate. About half the channel wjdth was sampled by electric fishing.

(iii) Longsl'ip Creek The sampling stat'ion consisted of a riffle-run sequence, which flowed into a pool about 1 m deep. The whole channel w'idth was electro-f jshed. R'iparian cover consisted of overhanging grasses, briar and willow, while instream cover was provided by overhanging banks.

(iv) Omarama Brìdge The sampi'ing s'ite was aìong the margins of the majn channel , where it flowed through a riffle and run. Water velocities were slower than at the Avon Burn site. There was no djrect rìparìan cover, although willows were growing about 10 m from the water's edge. Instream cover cons'isted of cobbles on the river bed.

(v) Chain Hills This s'ite was on a side braid of the river. The whole channel was electro- fished, and flowed from a riffle, through a run to the head of a pool. Some riparian cover was prov'ided by sfightly overhanging banks, and instream cover again consisted of cobbles.

4.3 Trout Tagging Trout were tagged with 'Floy' streamer tags during several different

sampl ing programmes:

(i) Trout larger than 15 cm caught during electric fishing. 18.

Lake Benmore (see ( i i ) Trout caught in gi'l I and sei ne nets during studies on section 4.6).

(iii) Trout captured durinq operation of the Ahurirj trap (see section 4.7 and Fiçt. 7).

(iv) As part of FRD's upper Waitaki fisheries studies, 5000 rajnbow trout (16-18 cm) were tagged with 'Floy' streamer tags in November 1975. Releases of 1000 fish each were made at five different locations in Lake

Benmore, jncluding a s'ite approxìmately 100 m from the Ahuriri Rjver mouth.

Each fish to be tagged was measured, weighed, and sexed when possible. Floy tag number, date anci locat'ion of rejease wei'e also i"ecorded. Recaptui"es ma.inly comprised angler returns, a'lthough some fish were caught by FRD and talaitaki Valley Accljmatísation Society (WVAS) staff. Generaì1y, the weight data provided by ano'lers was found to be unsu'itable for use in gr"owth jncrement calculations.

Many ang'lers still measure weìghts in pounds (lbs), and records of xå lbs or xå lbs were considered too inaccurate to indjcate changes'in weight since tagging.

4.4 Drift Div'ing This technique is used to assess trout numbers and dístribution in rivers wjth su'itable water clarity (Hicks 1979; Teirney 1979). A team of d'ivers in wet sujts with snorkels space themselves evenly across the river channel and float downstream with the current, counting all trout whjch pass under or around them. V'isual contact with the river bottom is ma'intained by duck-dìving when necessary in pools.

Two reaches of the Ahuriri have been drift dived as part of another study on the ¡iver (FRD's "Ten Rivers survey"). The first was a reconnaisance dive on 16 February Ig82, in the reach from Clay Cl'iffs to Chain Hills (F'ig. 6). The reach was d'iv'ided into two sections: C'lay C]'iffs - Omarama Bridge (approxìmately 11 km), and Omarama Bridge to Chain Hills (approxìmate'ly 7 km)" Total counts of trout were not made, since only two divers drifted each section. The river is braided'in this reach, and on'ly the main brajd was drjfted. Further, the 19. channels were large relative to visibility (only about 2 m on that day) and so compìete coverage was not poss'ible. The obiectives of the dive were to gain some understanding of the numbers of fish present, the relative abundance of brown and rajnbow trout and their distribut'ion and to ascertain the presence or otherwise of sockeye salmon.

sections, The second drift dìve was on ZI April LgB?, along FRD's hydrolog'ical length upstream of Ben Avon lagoons (Fig. 6). The sections are each 500 m in djvers' and the river flows 'in a s'ingle channel . The team consisted of four and two surveys were made through each section"

q L ,Annl rrrJ ¡ orer Srrrvcvs

The fishing season for the Ahuriri River downstream of the Longs'lìP confluence is from the first Saturday in November until APrì1 30. However, the river upstream of Lon.gs'lip Creek may be fished only from the first Saturday daily in December until April 30. Artificial ba'it only is perm'itted and the j bag limit is 10 trout, of a minimum size of 25 cm fork l ength (lrla'itak Va'll ey

Accl imati sati on Soci ety regu'l at j ons ) .

gpenìng day creel censuses were made for the l97B/79 and 1979/80 fishing jnterviewed downstream seasons. WVAS staff and councillors anglers on the river of Longsl.ip Creek, and recorded details of their catch, number of hours fished' These home acclimatisation district, etc. on a standard form (see Appendjx I). forms were also used for interviews carried out at random during the t978/79' 1980/81 and 1981/82 angl ing seasons by FRD staff'

To obtain information on the distribut'ion of anglers on the river, an aerial count was made on opening day in November 1978. Dajly ang'ling d'iary data were available from the Oamaru Ang'ling Club for the 1978/79 season and for the opening weekend in November 1979.

From 1947-1967, the N.Z. Marine Department collected angling statistics

through the New Zealand national angling diary and postal questionnajre schemes 20.

(Graynoth Ig74). Data for the Ahuriri River were presented 'rn WVAS's di strict report (Graynoth and Skrzynski 1973) and have been extracted and compared wìth angling statistics collected during this study'

4.6 Lake Benmore Studies Trout stocks'in the hJaitakì hydro lakes have been monitored on occasions since Benmore was filled in December 1964. Data which have been drawn on for incorporatig,n in this report'include angling diaries (1969-1973 and 1978-81) and results of gi11 and sejne netting programmes (tgZS and 1978-1981)'

4 .7 Trappi ng

n.ar small hvdro oroposal bv Waitaki nJÂc Yqt fv vrnf thc inr-rec.ticaf-ionerJsvr Ínto the Electrìc Power Board, the river was trapped at a site above the Avon Burn confluence (Fig. 6) durìng 1978 and 1979- The trap was constructed by both FRD years. and tnJVAS staff , and operated by WVAS staff during both

A lead-in, consìsting of a fence of cyclone wire was anchored to one bank of the ¡iver and stretched across the river, obliquely to the current. The end was attached to a fish hold'ing pen, made of cyc'lone wire stretched over a galvanised tubular steel frame (FiS" 7). The lead-in was kept upright with a taut cable, but could be lowered during floods by releas'ing the cab'lerpermitting debris and flood waters to flow past the trap. Fish could onìy enter the holding pen from downstream. All fish caught were we'ighed' measured and sexed, tagged w'ith a numbered ' F1 oy ' tag , and rel eased.

Unfortunately during both years, floods and generally high river flows seriously affected trapping operations. In 1978, the trap operated from 1-23 September, but only seven brown and 15 rainbow trout were caught during the period. In L979, the trap was installed on 6 August and washed out on 10 September, and th'is period included several occasions when it did not operate due to floods. Nine brown trout and one rainbow trout were caught.

4.8 Spawning Surveys Trout spawnìng surveys on the Ahurjri Rìver and tributaries have been made 2t.

FIGURE 7. Fish trap on the Ahurjri River, upstream of Avon Burn confluence. 22. each year since Ig75, with one previous survey of 0marama Stream, Hen Burn and Longslip Creek ìn June 1973. Two methods have been used - foot surveys and helicopter surveys. In both cases, the number of redds and fish observed was recorded, although ìt was not possìble to differentiate between the two trout species using the river grave'ls. Foot surveys tended to result'in lower numbers of fish being observed than helicopter surveys, owjng to the diffìcu1ty of see'ing clearly into the water from the bank.

The results provide only spot counts of fish and redds and cannot be used to est'imate the total run of spawning fish. Brown trout spawn earl'ier than rainbow trout, and the surveys were tìmed to approximate the peak of spawning activity for each species. Brown iroui were surveyed in junei Juìy, i'aiirbows ii¡

September.

4.9 Sockeye Salmon Studjes In 1975, FRD commenced studies into the biology and fisheries potentìal of 'in sockeye salmon (oncorhgnchus nerka). The main populatjon resided Lake Ohau

(Fig. 1) and spawned in tributary streams, primarily Larch Stream (Sgg:560836).

However, FRD also ascertained that a large proportion of the popu'lation reared for one to three years in the Ahuriri and North (Haldon) Arms of Lake Benmore (Graynoth 1978a).

Each year since 7976, FRD has erected temporary traps on Larch Stream, the principa'l spawning stream, and monitored the number of spawning fish, their size, sex ratio, age composition and other features (Graynoth 1978b). Systematìc echosoundìng and gi11 netting surveys of the Ahuriri Arm of Lake Benmore were also undertaken during 1979/80.

Prior to 1980, fìsh maturing in Lake Benmore migrated up the Ohau Rjver and through Lake Ohau to their spawn'ing streams. However, in 1980 the'ir route upstream was blocked by the Lake Ohau control we'ir and now by the new Ruataniwha

Dam and reservoir (F'is. 2). 23.

Consequent'ly, major fish salvage and transfer operations were mounted in

1979 and 1982 to relocate fish and to attempt to establish new runs into tributaries of Lake Benmore (Graynoth 7979, Hawke 1982). The principal release locations have been the Tekapo River, Mary Burn, Ahuriri River and Omarama

Stream.

In March 1979,7500 mature fish were trapped in Larch Stream and transferred; 1000 fish were released into the Ahuriri River at Omarama Bridge on S"H.8 and 2000 into Omarama Stream, just above the township (5117:656389). In addition, ova were artificially fertil'ised and reared at FRD's Silverstream Hatchery and 10 180 ad'ipose finclipped (7.2 grams) finger'lings released into the Ahuriri Arm of Lake

Benmore in 0ctober 7979.

After release, the mature fish successfully spawned and development of the eggs was monitored over the next few months. Although Omarama Stream is not an ideal habitat for rearing sockeye salmon (because of its relatívely high autumn water temperatures, floods and bed sìltation), the maiority of the eggs hatched and the young fry would have rapid'ly migrated downstream through the Ahuriri River to Lake Benmore.

Two years later, in 1981, a trap was erected on the Mary Burn in order to catch returning two year old sockeye. None were caught and none were observed spawn'ing in 0marama Stream. However, this was not unexpected, because the numbers of young two-year-oìd spawners can be qu'ite variable from year to year.

In early February 1982, reports were received of many thousands of sockeye congregating below the Ruataniwha Dam. Maior sa'lvage operations lvere undertaken on 18 and 25 February and 8700 mature fish were transferred, including 2100 and 450 to the original release locations on the Ahuriri and Omarama respectively.

In early March 1982, approximately 800 fish were observed spawnìng in the

Omarama Stream in the vicinity of the oxidation ponds, downstream of the township

(5109: 675403 and 675407). Releases in the Fraser Stream near Twizel were monitored and although there were losses due to floods, some fry emerged in June, 24. and were captured in a spec'ial trap downstream of the redds.

4.10 National Angling Survey In L979, FRD together with the New Zealand acclimatisation society movement began a posùal survey of anglers in all acclimatisation districts w'ith significant sales of fishing ljcences. The survey had four major objectìves:

(1) To collect, directìy from the adult angling population of New Zealand, quantitative and comparative information on every river supporting a significant sports fisherY.

(Z) To 'identify those attrjbutes which characterise particular rivers of

'importance .

(3) To determine from this informat'ion those rivers which constitute fjsheries

of nati ona'l , reg i onal and I ocal 'importance.

(4) To obtain a data base for future work.

Lake fisheries were deliberately excluded from the survey, since it was considered impractical to design a s'in91e questionna'ire capabìe of adequately coping wjth the full range of lake and river fisheries.

A quest'ionnaire booklet, containing a list of rjvers within a given acclímatisation district, was ma'iled to anglers'in each soc'iety. Anglers were asked to identify rivers which they had fished over a three to five year perìod by assessing, for each river, its importance to them (on a 1-5 scale), and the relatjve importance of seven listed qualities (dìstance from home, access' area of fishable water, scen'ic beauty, feeìings of peace and solitude, catch rate and size of fish) in determìn'ing why they fished that particular river. Informatjon was also requested on average number of vìsits, reach of river fished, fìshing methods used and any assoc'iated recreational activ'ity.

The Ahu¡iri River lies wìthin the hlaitaki Va11ey Accl'imatisation d'istrjct. In March 1980, survey booklets were mailed to 503 anglers selected at random ¿5. from the 3041 Waitaki Val1ey adult licence holders. The responses of 199 (40%) of the anglers sampled who returned booklets providing information on Waitaki Valley rivers established the regional s'ignificance of the Ahuriri Rjver (Teirney, Richardson and Unwin 1982).

Since their report was compiled, analys'is of the survey data has continued, to the point where rivers can now be evaluated in a national as wel'l as regional context. In particular, there are three aspects of the survey results which were not included in the original report, but which provide further evidence of the value of the Ahurirj. F'irstly, analysis of data prov'ided by anglers who travelled from other acclimatisation districts to fish the Ahuriri has been completed. Secondly, estimates of angler usage have been made, in terms of both the number of anglers and the total effort. Thirdly, based on an assessment of the results for the whole of New Zealand, a scheme has been set up for identifying and class'ifyìng rivers of national importance (Appendix II). Together with the information presented 'in the pre'liminary report, these additional results have been used to further assess the value of the Ahuriri.

5. BOTTOM FAUNA

A summary of the most extensive series of benthic invertebrate samples for any sampling occasion (2 Ju'ly 1979)'is given in Table 1. Ephemeroptera (mayflies) dominated all sampìes except Avon Burn confluence, where Diptera (flies) were more numerous. 0f the mayfly species recorded, Dereatidiuar spp. were the most common. For instance, they comprised 94% of mayfì'ies recorded from Omarama Bridge and 98% of mayflies from Longsììp Creek. cot-oburiscus humerat-is was the next most abundant mayf'ly , at" 4% and 2% for these two respectjve s'ites.

Several species of caddis (Trichoptera) were identified and the percentage of the four major spec'ies from Longs'lip Creek samples, with Omarama Bridge data

in brackets, were as follows: pgcnocentrodes Spp. (common stonycased caddis), 26-

spp. 27% (26%); olinsa fered.asi; (horny-cased caddis) 38% (S%); Hsdtobiosis (green free-liv.ing caddis) L3% (23%); Aoteapssche spp. (common netbuilding cadd'is) Creek were Z0% (32%). Among the D'iptera,52% of those recorded at Longslip simulids (sandfly larvae) and 48% chironomid (midge) larvae. Equìvalent figures for Omarama Brjdge were 67% and 35%.

(mean TABLE 1. Benthic invertebrate samples collected on 2 July 1979 number of animals from five samples/locatìon).

Tri butaries Ma'in stem

-:¿ -v(u o Trwr (U (lJ ! (-)(ui U1 (J c()G) () o c !ç o-E rg 5(lJ .r (L) rõ o É5 EaJ - a ro rd -5Ul- rõ 9) c (f) s-c) çq- cD q- !-! E rõ 5- c oc cc ld 'r rõ o EÐ (u >o oo FS- -c J o../) co <() J(J oco (J

Neu roptera 8 2 2

Ephemeroptera 1352 3418 2072 1076 1952 3 170 2010

6 22 LI4 P1 ecoptera 8 2 6

Tri choptera 758 1658 r22 286 94 150 656

138 598 Co1 eoptera 6B 168 10 L4 10

Di ptera 816 990 352 3256 944 2456 t342

Crustacea 30

Pl atyhelmi nthes 1B

0l igochaeta 626 936 t78 8 13 46 r02

Mol I usca 378 17B 4

Mi scel I aneous 2 28 I 2 4 6 r24

No/m2 4016 7 428 2682 4652 3023 598B 4948

Although all the data are not presented, some seasonal trends were apparent with highest numbers of invertebrates recorded during w'inter, the period of coldest water temperature but most stable and lowest flow. Substrate stab'ility is thought to be the most important factor associated w'ith h'igh densities of 27. organisms. In this regard, the tributaries are more stable than the main rìver, as jndicated by their higher densit'ies, smaller range (Table 2), and also the specìes composit'ion. Mollusca (snails) and Platyhelminthes (flatworms) are indjcatìve of relatively stable condit'ions, and both these groups were virtually confined to tributaries. The tributaries also contained a more diverse fauna than the main river.

TABLE 2. Range and mean density/n2 of benthic invertebrates at all sampling sites during 1978/1980.

Tri butari es Mainstem

(u GJI (J o- Ë ugt- cl (u all rõ rõ EcJ vl rú ro = t/i -!.- =l I rõ o) q)(u-y, 3,(u c ç gl+ o)(uq- I !1J =Ø ç(IJ rõ! co o5-c c (u c I ru.- tõ- F+J (u> >50 o!o I E! -C'F os-(J tr) () J(-)o oco (J- -J O co<

Total sampl ing occas'i ons 4 1 2 4 3 5 5

Maximum densi ty/n2 5398 2682 5394 3023 59BB 4948

Mean density/n2 3 564 1939 2794 t449 23LI 1689

Minimum densi ty/n2 r577 1 196 352 532 746 427

6. FISH STOCKS

Native and introduced fìsh specjes are both present'in the Ahuriri River.

The natives are represented by five species - two bull'ies, two gaìaxiids and one eel. Introduced species are all salmonids - brown trout, rainbow trout and sockeye salmon.

In comparison, Wing (tglg) recorded seven species of natjve fish and four introduced salmon'ids from other rivers and lakes in the upper l,laitaki area.

Quinnat salmon have not been caught or observed jn the Ahuriri River. However, in the past they have been caught by anglers in Lake Benmore, and in recent years' in Lake Ohau and adjacent hydro canals (E. Graynoth pers. comm.). There is a 28. possi b'i1 i ty that a smal'l spawnìng run exjsts in the Ahuriri R'iver, and there maY be potential for establishinq runs of this valuable sports fish, although the devel opment of a sea-run is prevented bY hYdro dams downstream.

0f the two addjtional native spec'ies noted by Wing (1979), Gafaxias ptosnathus while is rare, and has been recorded so far only from streams above Lake Pukaki, the shortfinned eel does not penetrate inland as far as the Ahuriri River.

6. 1 Comtron Bul ly ( Gobjo¡norphus cotj¿ianus)

The most abundant of the native species, the common bully' occurred at all five sampling stations jn the Ahuriri. 0f the 190 fish recorded during the eight rnq lÃÃot'\ r.rar,.a frnm Chain and 52 (27%) from the 5ctlllPl^^--1.:-^ lll9 ^^h-:^rêPtrl luuJ¡ IvJ \JJtol ttwt e I r vrr¡ thc Hills s'ite 'length gmarama Bridge s'ite. The mean of bul I ies increased with i ncreas'ing d.istance upstream, i.e. for February 1981, mean lengths were Chain Hills 4.0 cm (n = 50); gmarama Brjdge 4.0 cm (n = 36); majnstem at Longsl'ip Creek 4.6 cm (n = 3); ma'instem at Avon Burn 5.6 cm (n = 22). Size range recorded was Z.O - 8.2 cm. Densitjes at Chain Hills varied seasonal]y from an average of 1.6 fi sh/n2 during February-l4arch to 0.15/n2 in October.

These data are consistent with the probable life history pattern of the species. Adult fìsh spawn in the river during spring and summer and the larvae move downstream into Lake Benmore. Juvenile fish then make their way progressively upstream during summer. in addit'ion, l arge numbers of common bul l ies occurin

Lake Benmore and many of these probab'ly move freely between the I ower reaches of the river and the lake.

6.2 Upland Bull.y (cobiomorphus rtev:þsp) Although the up]and bully is probab'ly the commonest and most uridespread bully in the South Island (l'lcDowall 1978), 'it is not very common in the Ahuriri

and constjtuted only 7% of the bu1]y samp'les. Upland bull'ies were recorded from the Chain Hills and Avon Burn sjtes on'ly. Mean length was 7.9 cm, somewhat larger than the common bul1Y. 29.

Unlike the common bul'ly, the young of the upland bully do not have an active downstream migratory phase and it is likely that they undergo the whole of their life h-istory within the river jtself. Breedjng occurs during spring and summer, eggs are laid in a crude nest and the larvae and juveniles live in the shallow margins of pools.

6.3 Koaro (cal-axias brevipinnis) This whitebait species has been recorded from the Ahuriri River (t'ling 1979), although 'it was not encountered during electric fìshing. Adults penetrate well upstream'in trjbutaries and v¡ould occur above the regular sampling sites. Normal adult size range is i6-18 cm. It is probable that spawnìng occurs within the adult habitat with ljttle or no breeciing migraiion. i'iewìy ha'uched iuvenjles pass'ively migrate downstream with the river flow and rear in Lake Benmore. Once they have grown to whitebajt size'in the lake, they commence shoa'ling and move back up the Ahuriri during spring and early summer. Shoals of koaro whìtebait have been observed in the lower and middle reaches of the Ahuriri during January.

Thus, the river-dwelling koaro populations use Lake Benmore as a iuvenile rearing area'in a similar fashion to the way'in which populations in the lower l'la'itakì use the sea.

6.4 Common River Galaxias (cafaxias vuTsaris) This specjes is so-called because it'is the commonest and most widespread of the gaìaxiids jn the rivers of Canterbury and Otago (McDowall 1978).

IrJ'ithin the Ahuriri system it was recorded from the main river sampling sites

only. It was more common at upstream sjtes than downstreaml numbers recorded at the various sites were Avon Burn 20, Longs'lip Creek confluence 28,Omarama Bridge 13, Chajn Hjlls B. 0verall,'it was less abundant than the common bully' averaging 1 fish per 22 m2 in the main river. The mean length of 38 fish

measured ìn April 1981 was 7.2 cn, w'ith a range of 4.7 - 13.6 cm. The 13.6 cm fish ìs considered large for this species and, according to growth rate data jn Cadwallader (1978), would be seven years o1d. The maiority of the fish (23)' 30. were less than 7.0 cm ìn length and would be jn their first year of l'ife.

they Common rìver ga'laxìas live in moderately swift-flowing waters and since are strongly assoc'iated with cover, they are rarely seen. Spawn'ing takes pìace from wjnter through spring. As juveniles are often found in the same localìty as adults (Cadwaìlader 7976),'it is assumed that spawnìng occurs in or near the adult habitat. Shoals of juvenjles are frequently observed in the quiet-f'lowing margìnal shalIows of rivers.

6.5 Lonqfinned Eel (enquil-La dieffenbachii) Longfinned eels are known from the Ahuriri River but were not recorded durìng sampling. They are always closely associated with cover (deep poo1s, undercut banks, instream debris clusters, etc.) and are known to establish territorjes within thejr habjtat. Longfinned eels less than 60-70 cm are opportunist scavengers' feed.ing on any ava'ilable terrestrial and aquatic invertebrates, but eels larger than 70 cm are primarily fish eaters (Jellyman in prep.). The maiority of eels in the Ahuriri system can be expected to be larger than 70 cm. For instance, in

a samp'le of 154 longfins from Larch Stream (a tributary of the Hopkins River, Lake (FRD ghau), 97% were larger than 70 cm, with an average ìength of 87.7 cm unpubl'ished

data ) .

The absence of smaller eels is a consequence of hydro developments with'in the Waitaki River. Freshwater eels breed at sea, although the precise spawning

grounds of New Zealand species are unknown. Transparent iuven'ile eels (glass eels) arrive in river mouths during late winter and spring, and migrate during summer.

These young elvers are known to be able to climb the Waitaki Dam but it is very doubtful whether any can negotiate Aviemore. Climbing ab'ility is dependant upon size and very few elvers arriving at Aviemore are less than LZ cm - the maximum s.ize for vertical cf imbing. Therefore the popuìations of eels upstream of Avjemore are relìct populations and are gradua'lly being depìeted by commercial eel fjshing, the seaward migration of sexual'ly maturing adults, and natural mortalìty.

6.6 Brown Trout (sa-zmo trutta)

Brown trout were first introduced 'into the Ì,laitaki River system between 31.

1870 and 1BB5 (Hobbs 1948). They quickìy became established and are presently found in the main river, all major tributaries and the three source lakes. Stocks were managed'in the past by annual releases of hatchery-reared fish. However, this practice was found to be both expensive and unneccessary and has been discontinued since 1968. Emphasìs in management today is on protect'ion of the wild stocks from the adverse effects of water abstraction, river control schemes and power generation flow fluctuations (Graynoth, Pierce and Wing 1981).

6.6.1 Juveni I es Juvenile brown trout were the most common fish recorded during electric fishing and were present at all samp'ling sites. Highest densities were recorded from Longs'lip Creek, with a mean dens'ity of 0.79 fishinz. Densiiies for main rjver sites were less, w'ith O.?4/m2 at Chajn Hills, 0.22/mz at Omarama Bridge, O.7L/m2 and 0.08/n2 at Avon Burn and Longslip confluences respectively.

Brown trout less than 5 cm were recorded during December, with the occasional small specimen in February. A'lthough the largest fish captured durjng e'lectric fishing was 20.5 cm,90% were less than 10 cm in length. Figure 8 shows the trend ìn length frequencies of three brcwn trout samples taken two months apart. (N.8. The December 1977 sampìe is from Chain Hills as Longslip Creek was not sampled at thìs time. However, the mean lengths of samples from both sites during February 1978 were similar, indicating similar growth trends.) A wide range ìn length of the fish deveìops over time, reflecting both different hatching times and rates of growth.

Spawn'ing and rearing takes place'in both the main river and tributary streams. Although densities of juveniles in tributary streams exceed those in the main river, the total rearing habitat in the rjver ìs greater and hence greater numbers of juveniles can be expected to rear in the river than in tributaries.

6.6.2 Species proportions and di stribut'ion 0f all juvenile trout captured during electric fishìng, (n = 586), 65% were brown trout. Since samp'l'ing vras carried out at a variety of habitats and times, 32.

BRObIN TROUT

Chain H'ills (n=a8) L4.L2.77

20

10

Longsìip Creek (n=35) I .2.78 2A

10

Longs'l i p Creek (n=76 ) 7 .4.78 20 l¿l o--J >- 1^ ./l

É. lrl co = RAINBOl,l TROUT

Longs'lip Creek (n=35) 9.2.78 20

10

Longsìip Creek (n=29) 7 .4.78

20

10

45678 10 11 L2

F0RK LENGTH (cm)

FIGURE 8. Length frequencies of brown and rainbow trout sampl ed by electric fìshing, December I977 - April 1978. 33. this percentage ìs regarded as being a true reflectìon of the relative proport'ions of each spec.ies throughout the river. Unfortunate'ly,'insuffic'ient trap data were collected to relate the proportion of juven'ile fish to migrating adults, but data on adult species proportions are ava'ilable from drift dìvìng counts and angl ers' catches.

The reconna'isance drift dive during mid-February l9B? from Clay C]iffs to Chain H.ills, resulted in counts of 243 brown trout and 341 rainbows, giving relative proportions of 42% and 58% respect'ive1y for fish ) 25 cn. 0f the fish recorded in the 11 km upstream of Omarama Bridge,47% were rainbow, while downstream the figure.increased to 64%. A drift djve in Aprìl L982, in coniunction with the

"Ten Rìvers" survey, counted 14 fish, all brown trout, ìn two 500 m sections upstream of the gorge.

Data collated from anglers'catches (Table 3) show that brown trout constituted

64% of the total fish caught, and 68% of all fish kept. A'lthough Table 3 indicates three data sets where the percentage of brown trout is less than 50%, these correspond to small samPle sizes.

An explanation of the predomjnance of rainbow trout in the drift d'iving counts

compared with the h'igher proportion of browns in anglers' catches ìs put forward in the discussion (Section 8).

Analysis of the three seasons of anglerinterview data gives some informat'ion on the relative d'istribut'ions of both trout species. 0f the 29 flsh caught'in the upper reaches,24 (83%) were brown trout. Equivalent figures for brown trout in the mjddle and lower reaches were 11 fish (85%)'in the middle and 21 fjsh (47%) in the lower. it appears therefore that most rainbow trout occur in the lower reaches, while brown trout dominate upstream areas.

During the months of November and December,30 fish were captured in the

lower reaches, of wh'ich 56% were brown trout. This compares with four brown trout (27%) out of 15 fish caught during the rema'inder of the season. Although the numbers of fish'involved are few, they may indicate a seasonaì migration of 34.

TABLE 3. Summary of trout size data from Ahurirj Rjver angìer catches, I962-L982.

Brown Trout Rainbow Trout ol lo *Source Year Mean Mean Brown 'length Trout No. No. äo" No. I çngth caught kept (cm) caught kept (cm)

1962/63 D 55 34 54.4 32 20 38.6 63 t967 /68 D 93 70 45.2 30 23 45.0 76

L972/73 D 49 28 49 .0 22 7 43.3 69

1973/74 D 11 10 47 .5 I2 2 40.0 48

1977 /78 D 22 77 26 I7 46

1978/79 D 18 t2 49.7 7 1 72

57 1978/79 # I 43 34 48 .0 33 26 45. 5

1978/79 D (Ac ) 15 15 52.5 5 4 44.0 75

1 43 t979 /80" D (AC ) 9 9 54.6 t2 72 50.

1980/81 I 47 42 49 .0 23 16 35.0 67 t98r/82 I 22 18 54 .5 11 9 67

Total 384 289 2L3 137

Grand mean length (cm) 47.2 42.6

Species proportion (%) 64.3 35.7

* Source: D = Angler dìary D (AC) = Angling club d'iarY I = Interview

ô = Opening weekend # - Includes openinq day interviews 35. rajnbow trout into the lower river from Lake Benmore during the later part of the angling season. Considerably more data would be required to confirm this.

6.6.3 Size given jn A summary of all available trout length data from angìers' catches is

Table 3. Djrect comparisons between years are difficult as d'iarìsts frequently measured all fìsh caught, while interviewers measured only fish kept. However' overall a high proport'ion of fish caught were measured - 87% of brown trout and (the 16% of rainbow trout. Assuming that all fish greater than 25 cm legal l'imit) were kept, then 75% of brown trout caught were takeable fish. Max'imum size recorded for brown trout was 69.0 cm and 3.3 kg (length and weìght do not correspond to the same fish). The range'in length of the seven brown trout trapped at the Avon Burn site was 55-64 cm, with a mean of 57.3 cm. As these fish were all 'spawners', theìr mean size would be expected to be greater than that of the angler-caught fish (47.2 cm).

6.6.4 Movements A total of 27 tagged fish was recaptured, of which 10 were brown trout.

These were variousìy fish tagged in the Ahurirj River and recaptured there or in

Lake Benmore, or fish tagged'in Lake Benmore and recaptured in the Ahuriri River.

A summary of movements for both spec'ies is given in Table 4. This table ind'icates that considerable movement takes place between the lake and the river for both species, but fish tagged'in the river were generally recaptured there.

TABLE 4. Recaptures of trout tagged in the Ahuriri River and Lake Benmore.

Recaptured in:

river mouth mainstem upstream

BT 3 3 Lake Benmore RT 3 5 Tagged ì n:

4 Ahuri ri BT River RT 1 2

BT= brown trout RT= rainbow trout 36.

Although the data are few, it seems reasonable to'interpret them as represent'ing both a migratory population of fish which move'into the river to feed and/or spawn, and a resident populatìon of river fish' Thus brown trout tagged in the river were recaptured in the mainstem" In the lower reaches of the river, it is l.ikely that fjsh move regularly between the river mouth and the lake, Most especia'l1y during t'imes of flood when they would seek refuge in the lake' of the lake-tagged fish were recaptured in the river during November, but this probably represented commencement of the angling season rather than an influx of fi sh 'into the river.

6 .6 . 5 Dens'i tY The figures from the February 1982 drift d'ive gave a density of brown trout (size > 25 cm) of 15 fish/km. There were cons'iderable differences between the two areas surveyed, with an average density of 9 fish/km from Clay Cl'iffs-Omarama Br.idge and 30 fish/km from Omarama Brjdge-Chain Hills. Over the 16 km of rjver surveyed, a mean density of 25 trout/km (both spec'ies) was recorded'

Add.itional fish counts were obtained during the spawning surveys (see Table 7). Redd counts made during these surveys were considered as either brown trout or rainbow redds according to the month of survey, (brown in June/July, rainbow 'it in Sept.ember). Although fish counts are apparently presented 'by species', was not possible to differentiate between the two spec'ies during the surveys. Therefore the fish count appearing under either the'brown trout'or'rainbow trout' sections of the table, is actually a composite count of both species. Since these data are not spec'ies specific, they are discussed below and not repeated in the rainbow trout section (6.7).

l^lithin the majn river, the lowest count of trout (47 in July 1975) corresponded with the'largest number of redds. Th'is may in part be due to brown trout having left the spawnìng areas, but is also due to the 1975 survey be'ing done by foot whereas subsequent surveys were by he'licopter. Greatest densities of fish were in the Lake Benmore-Qmarama Brjdge area, where 39 fish/km were recorded in 37.

September Lg77,26 flsh/km in June 1978 and 14 fìsh/km in June 1979. The maximum jn density recorded from a tributary was 10 fjsh/km in Omarama Stream June 1978.

Fjsh densjties recorded during the spawnìng season were less than those during the drìft dive of the 0marama Brjdge-Chain Hills sectjon. However, spawn'ing counts were prìnc'ipally of spawnìng fish, with an anticipated m'injmum size of 33-34 cm (FRD unpub'lished data - Tekapo River trap 1982), whereas the drjft d'ive counted all fish ) 25 cm'

6.6.6 Growth rate Length increments have been calculated for recaptured fish whìch were at f iber"ty fot^ more than 150 days. Results are presented in Table 5. On'l¡r relatively large brown trout were recaptured and the average'increase'in size for those fish, which were 40-50 cm at tagg'inq, was 3.5 cm/year.

TABLE 5. Growth 'in length of tagged trout.

Length at Length at Growth Spec'ies taggì ng reca pture Days until Increment (cm) (cm) recapture ( cm/yr)

Brown trout. 42.L 51 .3 583 5.8

43 .3 55.2 639 6.8

46.5 51 .3 Li44 1.5

47.5 53 .0 1465 r.4

47 .B 51.5 752 1.8

55.9 64.1 TI97 2.5

Rai nbow trout 16 .8 45. 1 832 L2.4

t7 .4 34.3 310 19. B

17.4 40.5 500 16.9

17 .8 48.3 733 15.2

22.5 30. B 154 19.7

30.2 54.2 937 9.3

31.1 39.0 478 6.0 38.

6.6.7 Spawni ng The spawning season of brown trout is earlier than that of rainbows. Records from fish traps on the Tekapo River and Mary Burn (a maior spawnìng tributary of the Tekapo River)rshown in Tab'le 6, jndicate that over half the Ùotal run of brown trout have migrated upstream for spawning by the end of May and over 80% by the passing end of June. Some migrations occur as late as September, although frsh through the trap at this stage include immature fish'

TABLE 6. Summary of upstream trout catches at Tekapo River and llary Burn traps, total number of fish passìng through trap)'

n T^ r- 1 Apr May Jun Jui AU!J )ep lULcll

Brown Trout

Tekapo R'iver n 67 594 396 8B 23 104 r272 100 % (cum. ) 5.3 52.1 83. 1 90.0 91. B

Mary Burn n 9 148 92 18 11 5 283

% (cum. ) 3.2 55.4 87.9 94.3 98.2 100

Rainbow Trout

Tekapo River n 5 8? T7 68 L67 L20 459

% (cum. ) 1.1 19.0 2?.7 37.5 73.9 100

Máry Burn n 0 2 3 13 30 48 96

% (cum. ) 0 2.t 5.2 IB.7 50.0 100

Spawning counts on the Ahuriri River took p'lace during June or Ju'ly, when

between 80-90% of all brown trout migrat'ions can be expected to have taken place. The data (faUle 7) consist of numbers of redds and fish recorded on the day of the survey only. Thus they are underestimates of the total spawn'ing in each system. Also, because djfferent people were involved over the ten years of surveys, similar sections of each stream were not necessari]y counted on each occasion, and in several years conditions'in the main river did not allow counts to be made there. It ìs assumed that all redds counted in June-July are brown trout redds and conversely, that redds counted in September are those of rainbow trout. TABLE 7. Spawning counts in the Ahurirj River and tributaries, 1973-1982 (numbr:r of redds, with humber of fish in brackets; f ish numbers 'include both spec'ies).

-:¿c I c rd L (urO rõl I (u rõ -o rú Date !Eo) E(u tn Øç +Jø FF Ptn Its (h- rõ rú Ø _y. orõ J- oroo) rõ0) ç Ol¿ .rC =Eorõ fõ G) E r! !! >(+ >(F >G' crõ 5-(u cD(u !q) -o.r c rõ.- lõ'r lE'.r rg.r C (U .rP õs- cs- õ5- -(U cc) roL *J -vrúG¡ES- Ç 5--È lú !- rõo EÐ oJ5 :55 -5-.rP os- 'r *) !o --(J (J (J (J c7ó J(J OV' FF- JaOoCO ocô(J(J =F o.n -co =.n Brown Trout

June 1973 68 (78) I (4) t2 (7) 77 (8e)

July 1975 57 (3) 35 (0) 40 (24) 132 (47) 83 (4) 83 (4)

July 1977 t9z (54) 0 (0) 13 (7) 1e5 (61)

June 1978 20 (2r0) e (83) 2e (2e3) r21 (r24 0 (0) 721 (r24)

June 1979 31 (113) 21 (38 ) 73 (zeo) 125 (441) 56 (24) 0 (0) 0 (0) 7 (0) 24 (0) 87 (24)

June/July 1980 7 (t44) 7 (ee) 48 (2s4) 62 (537) 4 (3 ) 4 (3)

June 1981 e (e8) 2 (25)* 67 (r78) 78 (301) 13 (1) 13 (1)

June/Jul y 1982 7 (26) 3 (40) 58 (56) | 68 (rzz) 25 (5) 11 (5) 3 (0) 3 (2) 10 (0) 42 (0) e4 (10)

Rainbow Trout

Sept.7977 L2 (311) 45 (1le) 57 (430) L2 (24) 1(0) 15 (0) 28 (24)

Sept. 7979 16 (2) 3 (0) 1e (2)

Sept. 1980 0 (0) 3o (o) 3o (o)

Sept. L982 9 (13) ** 1 (50+) 10 (63+) 1e (0) 1e (0)

- = no data (, * = only two-thirds distance surveyed \o ** = no count, as water discoloured by bu]ldozer activity 40.

In the mainstem, most spaurn'ing occurs in two reaches of the river - upstream of the gorge and below Clay Cliffs (F'ig. 9). V'irtually no spawning takes p'lace in the reach from Ben Avon to Clay Cliffs. If this sect'ion is ignored, then the mean numbers of redds/km for the mainstem reaches are: 2.8/kn (lake Benmore- gmarama Bridge) ; 1.1/km (Omarama Bridge-Clay Cl iffs) ; 2.9/km (Ben Avon-Canyon Creek). In those years when relatively low counts were recorded, few redds occurred in the lower reaches of the river. In 1975 and 1979 when h'igher counts were made, numbers of redds in the'lower'and'middle'reaches ìncreased dìsprop- ortionately relat'ive to the upstream area. Th'is suggests that better spawning cond'itions may occur upstream and are used preferentia'lly by fish.

0f the tributaries where spawninq takes place,Omarama Stream is the most important. A mean of 89 redds per season was recorded from this stream, compared with a seasonal mean of 138 redds for all trjbutaries comb'ined. Spawning ìn gmarama Stream occurs princìpally in the lower reaches, but unfortunately there is ev1dence of increas'ing siltation, probab'ly attributable to upstream swamp drainage. Siltat'ion causes s'ignificantly l'ncreased mortal ìty of eggs within redds, due to decreased water circulation and oxygen availability.

Diadem Stream is extensive'ly used for spawning (average 6 redds/km),but is too small to reta'in post-spawned adults. Fish appear to hold after spawning only in Qmarama Stream, and to, â lesser extent, Longslip Creek. Although good spawnìng gravels are available in Longsl'ip Creek, fish are denied access to some areas by a waterfall. Some spawning takes place'in both the Hen Burn and Quail Burn but, as both have reaches that dry up in summer, they have limited rearing potent'ial.

The most extensive spawning survey data are for 1979 and 1982. In L979,

59% of all redds were counted in the ma'instem, compared with 42% in 1982. The greatest number of redds recorded was 215'in 1975. Assuming a mean length of female fish of 42.3 cm (the mean ìength of female brown trout from the Tekapo trap) and using the fecund'ity/length relationship of Allen (1951), then the estimated mean number of eggs per fish is 1630. Therefore, the redds counted in 1975 contained an estimate of 350 500 eggs. 4L.

CANYON CREEK

QUAIL BURN

WILLOWBANK STREAM HEN BURN ÙADEMy' STREAM

LAKE BENMORE

OMARAMA STREAM

FIGURE 9. Trout spawning areas in the Ahuriri River system. 42.

6.7 Rainbow Trout (satmo qajr¿nerjj)

Rajnbow trout were liberated in the Wa'itaki Riverin the early 1900's' some years later than brown trout. L'ike the latter, they rap'idly established and are now found throughout the catchment. Although not growing to quite the same sjze as brown trout, rainbow trout are more readì1y caught and are regarded by anglers as more vigorous fìghters than browns. Management emphas'is has been similar to brown trout, with the last major liberation of hatchery-reared fish being'in 1974 (Graynoth, Pierce and tJing 1981).

6 .7 .I Juven i I es 0f the 204 juvenile rainbow trout samp'led by electric fishing, 55% were jn Longslip Creek anci a further 28% irom the majnsi.etii at Longsì'ip C'r"eek confluence.

The mean dens'ity of juvenile rainbows from Longsìip Creek was I.2L/n2, wh'ich exceeded that for brown trout (0.79/n2). Dens'ities in the remainder of the main river were considerably lower than those of brown trout, and ranged from 0.)I/rnz - O.O5/m2. From the limited data available, ìt appears that rainbows make relatively less use of majnstem rearing habìtats than do brown trout, wìth the maior proportion of ra'inbows rearing in tributary strearns. A maxjmum dens'ity of 5.4 fish/m2 was recorded from Longslip Creek during February 1978, wh'ich was greater than the 1.6 fish/mz recorded for brown trout at the same time.

Due to their later spawning season, ra'inbow trout hatch after browns. Smallest fish (2.5 - 2.6 cm) were recorded in December, while the mean sample'length at this time was 3.5 cm, compared with 5"1 cm for brown trout. This difference in mean size is evident by comparing length frequency histograms (Fig.8) with those of brown trout for the same period.

6.7 .2 Size Rainbow trout length data from angìers'catches were summarised in Table 3. Overal1,64% of all rainbow trout caught were takeable fish. The "grand" mean length (42.6 cm), was less than that of brown trout (47.3 cm). The maximum sjze of rainbows was also smaller (66.5 cm and 2.8 kg)" Spawn'ing fish recorded from

the Avon Burn trap (n = 15), ranged from 42-57 cm, with a mean sjze of 48.3 cm. 43'

6.7 .3 ltlovements

From data for the 11 rainbow trout recaptures (Table 4), there is again evidence of movement from Lake Benmore into the Ahuriri River" Four of the eight rainbow trout wh'ich moved from the lake jnto the river were recaptured during earìy April and three of these were caught near the river mouth. This may indjcate an autumn movement of ra'inbows into the river.

6.7 .4 Densi ty Densities of 7.5 rainbow trout/km and 52/km were recorded from Clay Cìiffs - gmarama Bridge and Qmarama Bridge - Chain Hills respectively during the February

1982 drift dives. The mean density of rainbows over the whole reach was 21lkm and exceeded that of brown trout.

Fish numbers recorded during spawning counts have been d'iscussed previous'ly

( see Sect'ion 6 .6 . 5, p.36 ) .

6.7 .5 Growth Rates The ra'inbow trout from 16.8 - 17.8 cm in length,'listed in Table 5, were all tagged in November 1975. These were al'l one-year-old hatchery-reared fish" Growth in the hatchery was relatively rapìd - up to 18 cm'in a year. Growth in the second year (after release into Lake Benmore) appears equally rapid, ranqing fron LZ-20 cm. Thereafter, the growth rate can be expected to decline rap'idìy to approximately that of the larger brown trout (see Sectìon 6.6.6, p.37).

6.7.6 Spawning

The main spawning period for rainbow trout in the Waitaki catchment is August-September. An early run of rainbows was recorded 'in May at the Tekapo River trap (Table 6), but there was no corresponding movement in the Mary Burn.

Records from the latter s'ite gìve a more accurate indication of spawning activ'ity as fish move into the Mary Burn princìpally for spawning whereas movements at the

Tekapo River trap include immature fish and fish moving upstream consjderably in advance of the spawnìng season.

Unfortunately, there are no comp'lete spawning counts for rainbow trout in the 44.

Ahuriri River (Table 7), so the relative importance of the ma'instem and tri butary spawnìng cannot be ascerta'ined. Diadem Stream is extensìveìy used, but 0marama

Stream appears less important to rainbow trout than to brown trout.

6.8 Sockeye Salmon (oncorhynchus nerka) Sockeye salmon were successful'ly introduced into New Zealand in 1902. The eggs were collected from sea-run fish in the Fraser Rjver, British Columbia and the young fry were eventual'ly reared and l'iberated into the Hakataramea River and tributaries of Lake Ohau (Thompson L922)" A sea-goìng popu'lation d'id not develop and the fish became voluntariìy landlocked,1ìving in Lake Ohau and spawning in tributary streams, such as Larch Stream (Stokell 1962, Hardy 1969, Flain I97I, . ^-^ \ Mcuowa I r L9/ó).

In jts native habitat in the I'lorthern Hemisphere, landlocked sockeye salmon (kokanee) are important pìankton covertors and are eaten by large trophy-size rainbow trout and other salmonids. They support valuable sports and commercial fjsheries in some of the'inland lakes of North America (Scott and Crossman 1973). The sea-run strain is also an extremely ìmportant commercial species throughout the North Pacific (Foerster 1968).

Recent attempts have been made by FRD to establish sockeye salmon in the

Ahuriri R'iver and Omarama Stream. If successful these experìments could help preserve the New Zealand stocks of sockeye salmon and lead to the development of significant fisheries both within the [,.laítaki Catchment and elsewhere.

The fate of fish released into the Ahuriri River in 1979 and 1982 is not known. In 1982 some probab'ly entered 0marama Stream and ming'led with fish released there. Others probably d'ispersed widely throughout the river seeking suitable spawning grave'ls. The success of the 1979 release of hatchery-reared sockeye into Lake Benmore'is also unclear, although a few were recaptured in gì1ì nets set in the lake several months later. A sample of fish was inspected below

Ruataniwha Dam in 1982, but none were finclìpped.

The overall success of these transplants could be uncertain for several 45. years. If the staff and funds are available then the Ahuriri could be surveyed jn February and March 1983, using drift divers and observations from helicopters' to detect whether four-year-old fjsh from the 1979 releases return to the river. gmarama Stream can easily be surveyed on foot. However,'it would be more econom'ical to delay these surveys unt'il 1985 when progeny of the 1982 releases should return.

In the meantime, FRD will continue stud'ies on the now remnant spawnìng runs into Larch Stream and will undertake further transfer operatìons when requ'ired.

FRD will a]so preserve a brood stock of sockeye salmon at the research facifity at Glenariffe on the Rakaia River.

7. RECREATIONAL FISHERY

Information on the recreational fishery has been obtained from a variety of sources, but is dealt with here in two parts. The first part (Sections 7.1 - 7.3) is data from angler diaries and intervjews, while the second part (Section 7.4) gives results from FRD's recent National River Angling Survey. Results from this latter survey for al'l major waterways w'ithin the hlaitaki Va'l'ley Acclimatisation Socìety district have been publ'ished in Teirney, Richardson and Unwin (1982). Ihe angling seasons for which ang'ler diary and interview data were available and the type of data per season were outlined in Table 3 (p.34). Data on size of fjsh were outlined prevìousìy in Sections 6.6.3 and 6.7.2.

7.I Catch Rates Catch rates, calculated from the ava'ilable data for all fish caught and for takeable fjsh, are gìven in Table B. The overall mean values indicate that an average of 3.2 hours'is spent to catch a fish, with 4.3 hours angìing per takeable fish. From the three years of angfing ìnterview data, ang'lers spent an average of 3.8 hours fishing per visit. Also, for these interview data,65 of the 134 anglers jnterviewed had caught no fish - an average of 48.5% empty bags. 0f 42 intervjews conducted on opening day !978, only n'ine empty bags (21%) were recorded.

There were 149 records for rnethod of fishing, and 76% of anglers used flies, 46.

TABLE B. Ahuriri River trout catch rates, 7957-798?.

No. of Angl i ng No. of Hou rs Fi shlhr Fi sh/hr *Source di ary Season i nterv i ews f i shed (all ( takeabl e days ) )

1957 /58 D 43 163 0. 19 0.14

1962/63 D I4I 457 0"19 0.I2

1967 /68 D 114 396 0.31 0.23 r972/73 D 17 67 1 .06 0.52

1973/74 D 7 31 0.74 0.39

1977 /78 D 27 88 0.55 0 .39

1978/79 D 23 81 0.31 0. 16 rs78/79 I 53 293 0.26 0.20

1978/79 D (Ac) 161 0.t2 0.r2

Is79 /80 D (Ac ) 11 97 0.23 0.23

1980/8 1 I 53 162 0.43 0.36 r9B7/82 I 28 58 0.57 0.47

Total 383+ 134 2048

Grand mean (fish/hr) 0.31 0.23

*Source: D = Angl er d'iary D (AC) = Angling Club diary I = Interview 47. whìle 24% used sP'inners.

7 .2 Area F'ished

From the 1980/Bi and I98I/82 interview data, 79 records of locality fished were available. A total of 38 anglers (48%) fished downstream of the Omarama Bridge; 17 (ZZ%) fished the 'middle' stretch of river from the bridge to the gorge (although LZ of these fished within a few km of Omarama), wh'ile the remajning 24 (30%) fished above the gorge. Data ava'ilable from the 1962 and 1967 angling diary schemes ind'icated that 68% of al1 angling was within 0-10 miles (0-16 km) of the mouth, ZS% from 10-20 miles (L6-32 km) and the remaining 7% above 20 miles from the mouth. Both sets of data indicate that the area downstream of the gorge ìs the reach most heavily fished, with highest concentratìons of anglers within a few km rad'ius of Qmarama. An aerial count of 60 angìers was recorded at B a.m. on open day 1978, for the area downstream of Longslip Creek (the river above this 'is not open to angling unt'il December). This count gave an overall density of 4.4 ang'lers per km, although 7.5/kn vrere reÇorded belov¡ Omarama Bridge (F'ig. 10)'

7.3 Origin of Anglers

Ang'lers' "home acclimat'isation society" was recorded on the angler interview forms. After subtracting any repeat'interviews of the same anglers, the total number of separate anglers 'interviewed was 120. A breakdown of acclimatisation soc'iety districts represented is given in Table 9. Forty-e'ight percent of all

anglers came from WVAS, although this is fikely to be an over-estimate of the usual proportion of local anglers, as the maiority of the 1978/79 jnterviews (79%) were conducted on openìng day. (It is normal for a higher percentage of local ang'lers than visiting anglers to fish local waters on opening weekend.)

gccupancy records for the Omarama Camping Ground (September 1981 - January lgBZ) gave a total of 4601 vis'itors over this period, of which 1262 (31%) were

recorded as ang'lers (tr,I. Ward pers. comm. ). 0f these, 80% were from with'in New

Zealand and ?O% from overseas. This compares with figures from Hewson (1982)' which'indicated that 85% of all v'is'itors to the l¡laitaki Va]ley area durjng the 48.

FIGURE 10. The Ahuriri River at 0marama Bnidge, on State Highway 8. 49.

Christmas 1981 period included fishing as part of their activities and 15% came solely to fish.

TABLE 9. Home acclimatisat'ion society of anglers jnterviewed on the Ahuriri River, 1978-L982.

an Accl imati sation Soc'iety (u= +) ! 5- ln (u 5I +) (u ¡= 5- -o! L 5 (u (u o rO +) +J +) q- 'rJ c c o o c o rd ro +J (n O) rO Ð C-) (J O) rõ cc ! J- (u .rO (¡J -v c rO ç o 5 -c -c tJ1 -o +J +J O) -o +) P ! -Ulo)(Ú F :t rO ! J ! (u p an (u çq) = rõ o o o <..r1 = aJ') O U'' z. = O

7978/79 53 36 2 10 5

i980/B 1 39 1B 1 6 1 3 9 1

r98r/82 28 4 2 6 7 5 4

Total r20 5B 5 22 1 15 74 1 4

Further analysis of the 1980/81 and 1981/82 interview data showed that of the l'icence types recorded on 78 ìnterview forms,64 (82%) were adults (over 16 years) and L4 (I8%) juniors.

7.4 Value of the Ahuriri River Fishery to Anglers

7.4.L Summary of preliminary results

The following section is a summary of FRD's f\ational R'iver Angìing Survey results for the Ahurirì, as presented in the prefiminary survey report (Teìrney, Richardson and Unwin 1982). This report should be consulted for more detailed i nformat'ion .

The Ahuriri was fished by 83 (42%) of the i9B Waitak'i Valìey anglers who indicated which rivers they fished, and was exceeded in this respect only by the lower t¡Jaitakj River. The Ahuriri was very highly valued as a trout fishery, with

47% of the respondents considering it of except'ional importance. Again, the lower Wa'itaki River was the only other river in the district to receive comparable rati ngs. 50.

The'importance of the Ahuriri was reflected by the high ratings assìgned to the various characteristics investigated by the survey. It was the only trout fishery.in the district to receive except'ional ratings for three of the seven quaìitjes stud.ied (area fishable, scenic beauty and feelings of peace and solitude).

It was also high'ly rated for accessibi'lity, especìa'lly to the lower and middle reaches which were the most heavily fished areas. Catch rate and size of fish, although not considered by the respondents to be more than average, were among the highest in the district. The only characteristic of the Ahuriri consjdered to be below average was its djstance from ang'lers' homes, reflecting its location away from any s'izable population centre.

The impression of the Ahurjrì gaìned from these results is that of a very high quality trout fishery which attracts a hìgh level of usage, considering ìts isolatjon. Commenting on this, it was concl.uded (Teirney, Richardson and Unwin 19BZ) that ,'The Ahuriri is an extremely highly valued river fishery Although the lower reaches of the river now l'ie under Lake Benmore, the rest of the river and its catchment are v'irtually unmodified - the on'ly major fishery'in the upper Waitaki system for which this can be said. Thjs distinction, and the exceptionally h'igh qual'ity fish'ing ava'ilable on the Ahuriri, indicate that it .... is a river of at least reg'ional importance. "

7 .4.2 Vi si tì ng angl ers In addition to the 83 Waitaki Val'ley anglers who provided data on the Ahuriri a further 78 anglers from other acclimatisation districts'indicated that they fished the rjver. These anglers held licences from eight other accl'imatisat'ion d.istricts throughout the country (Table 10). This fact alone is an indication of the h'igh value of the Ahuriri - of all the rivers'in the South Island, only the lower Waìtaki and the Rangitata (both fisheries of national ìmportance) attracted more non-local ang'lers.

In general terms, the information provided by v'isiting anglers tended to re.inforce the characteristics of the Ahuriri already establ'ished by the local g'ivi ng angl ers . ¡ver 75% of the vi si t'ing angl ers regarded the Ahuri ri as remote, 51.

'it the lowest possible rating for distance from home. In all other respects, the ratings awarded by the visitors were equal to or hìgher than those awarded by local anglers. Area fishable, scenic beauty and feelings of peace and solìtude all received exceptional ratings, and were slightly more highly rated than by local anglers. More noticeable were the ratjngs for catch rate and size of fish, both of which were sign'ificantly more highly va'lued by visiting anglers.

Over 90% of the visitors considered the catch rate to be average or better, and

88% felt that the fish were of average or better size.

TABLE 10. Number of Nat'ional River Angl'ing Survey respondents who fished the Ahuriri R'iver.

Accl imati sat'ion di stnict Number of respondents

Auckl and 1

Wel I i ngton 2

Marl borough 1

North Canterbury 23

Ash bu rton 7

South Canterbury 10

Wai taki Va'll ey 83

Otago 29

Southl and 5

The major difference between visiting and local angìers was in their choice of angling methods (Fig. 11). Among local anglers, artificial sp'inners were the most popular lures, followed by wet flies. Nymph fishing was the least popular method, being practised by only 25% of the local angìers. By contrast, approx-

ìmately 60% of the visiting anglers favoured dry or wet flies, while 50% used nymphs. On'ly 34% reported using artificial sp'inners.

In terms of angling effort, local anglers appeared to make more vis'its per angler than did anglers from elsewhere. Local ang'lers recorded an average 52.

DRY FLY l^lET FLY NYMPH SP iNNER

FIGURE 11. Percentage of visiting and local ang'lers usi ng four angling methods on the Ahuriri River. (n= visitors; Efl = loca'ls) 53. of 6.5 r 1.5 (95% confidence limits) visits per angl er, whi'l e non-l ocal angl ers recorded 4.2 ¡ 0.9 visits. S'ignìf icantly more vi si ting ang'lers (48%) reported camping as an actívìty commonly associated with angling than did local anglers (33%).

The above results suggest that local and vis'iting anglers who fish the Ahuriri represent two distinct groups of anglers. In partìcular, v'isiting anglers appear to be more skilled than local anglers. Whereas local angìers favoured artificìal spìnners or wet fljes (generally regarded as less skillful methods), visiting anglers showed a preference for dry flies or nymphs, as weìl as wet flies. Sjnce successful use of both the dry fly and nymph genera'l'ly requires the angler to cast to a particular fish, these methods requìre a greater level of expertise than artjficjal spinners. The hìgher assessments of catch rates and size of fish by visiting anglers are consistent with this conclusjon. (Note that it is also possible that visiting anglers, by vjrtue of their wider angling experience, were in a better position to judge whether catch rates, etc. were above or below average. A characterist'ic of the survey results for the whole country was that anglers were in genera'l rather conservative in the'ir evaluation of catch rates. )

The reduced number of visits per angler, and the hiqher inc'idence of camping among non-local anglers, are consìstent u¡ith the greater distance they had to travel. Even more so than local ang'lers, these visitors to the d'istrict were evidently prepared to expend a considerable amount of time, energy and money in order to fish the Ahuriri.

7.4.3 Characterìstics of three reaches of the Ahuríri

In the survey booklet, ang'lers were asked to identify which of the "head", "middle" and "lower" reaches of each river they had fished. l^lhile these terms were not defined for each rivern local knowledge suggests that for the Ahurirj the three reaches correspond to: the source to the gorge; the gorge to Omarama; and Omarama to Lake Benmore. A'lthough there was a slight tendency for visiting 54. anglers to fish more in the m'iddle and upper reaches than did local anglers, the difference lvas not statistically signifìcant. Consequently, the results for this sectjon of the analysis were obtained by grouping all the data from local and visiting anglers giving a total of 161 responses.

From these replies, three mutually exclusive groups of anglers were selected.

Two groups, consisting of 30 and 34 anglers respect'iveìy, were made up of anglers who had fished only the lower reaches, or only the middle reaches. For these two groups, the replies can therefore be taken as indicatjve of just one particular reach, rather than the river as a whole. The third group was made up of 49 anglers who had all fjshed in the headwaters, as well as possìb1y one or both of the other two reaches. The information from these angìers cannot therefore be uniquely associated with the headwaters, but relates more to the whole river including the headwaters. The remaining 48 anglers fished both the middle and lower reaches, and were excluded from the ana'lysìs.

Generaliy, a'll three groups of anglers confirmed the assessment of attributes based on the original analysis. High ratings for ease of access, scenic beauty and solitude were gìven by aì'l groups. Scenic beauty and solitude, however, were particularly valued by those anglers who had fished in the headwaters. Scenery was rated as exceptional by 68% of these anglers, while over 70% raled the feeìing of solitude as exceptional. Both catch rate and, to a lesser extent, size of fjsh were rated d'ifferently by the three groups. Catch rates were considered above average by 25% of the anglers who fished only the lower reaches, and 36% of the anglers who fished only the middle reaches. The comparable figure for anglers who fished throughout the river was 65%. Similarly, only IB% of the anglers in the lower reaches considered the fish to be of better than average size, compared to 48% of the anglers in the third group.

Few clear-cut trends were evident between the three groups as regards preferred fishing methods. Wet flies were very popular in the lower reaches

(being used by 70% of the respondents), while the dry fly was used by 62% of 55. the anglers in the third group. However, in general all four fishing methods

(dry fly, wet fly, nymph and spinner) were used throughout the river. This indicates another sìgnificant aspect of the Ahuriri fishery, in that anglers have a wide range of fishing methods available to them throughout the length of the river.

In terms of the overall 'importance of the Ahuríri as an angling river, by far the h'ighest ratings were g'iven by anglers who had fished throughout the river, including the headwaters. 0f these anglers, 74% considered the Ahuriri to be of exceptjonal importance to them. ThÍs 'is consistent with their high ratings for scenìc beauty, solitude, catch rate and size of fish, and for many their willingness to travel long distances. However, it should not necessarily be concluded that these ratings apply only to the headwaters. Since many of the anglers in this group fished throughout the whole river (66% of them indicated that they fished all three reaches), it is likely that they represent the keenest and most energetic anglers. Consequent'ly, while their high ratings undoubtedly reflect some of the attributes of the headwaters, they can also be interpreted as the opinions of an enthusiastic group of anglers who have good first hand knowledge of the whole Ahuriri River.

7.4.4 Estimates of total usage The estimates of total annual usage presented in this section are based on the survey results, and are the best estimates that can be made with the avajlable data. However, they are subject to two limitations, which should be borne in mínd when considering the results.

Fìrstly, they are likeiy to considerably underestimate the total usage. Since on'ly adult whole season l'icence holders were sampled in FRD's survey, the results account for only a proportion of the angling effort wjthin each d'istrict. Both for the country as a whole, and for the lrlaitaki Valley accl jmatisation d'istrict, adult whole season ljcence sales in 1,978/79 represented about 56% of the total fishing licence sales for that season. In Waitaki Va'l1ey, there were 56.

3401 adult whole season licences out of a total of 6048, including adult, iunior and part-season licence holders.

Second'ly, since response rates for the survey were not high (typ'ically

7O%), and only a proport'ion of the respondents provided comparative data, for practical purposes the response rates were generally between 40% and 50%. Con- sequently extrapolating the data to allow for the non-reponse has the potential to'introduce some degree of bias. However, a comparison between the National River Angling Survey data and results from other recent FRD posta'l surveys suggests that this does not constitute a s'ignificant problem. In particu'lar, results from postal surveys of the Rakaia and Hurunui Rivers (Unwin 1980,1981; Davis 1982), both of whìch el'ic'ited responses of 90% - 95%, are consistent with results for those rìvers obtained from the national survey data.

TABLE 11. Estimated number of adult anglers who visit the Ahuriri River from each acclimatisation society district.

% contri but'ion % contribution Soci ety Estimated no. Estimated no. from each from each angl ers di stri ct of di stri ct of vis'its di stri ct

Auckl and * * * *

Wel I 'ington * * * *

Mar'lborough * * * *

North Canterbury 340 1B 1270 13

Ashbu rton 60 3 280 3

South Canterbury I20 7 420 4

hlai tak'i Va1 I ey 930 51 6020 61

Otago 330 1B 1520 15

Southl and 60 3 370 4

Total 1840 100 9880 100

* Too few responses to est'imate. 57.

EstÍmates of angler usage of the Ahuriri are given'in Table 11. Confidence limits have not been included, since for the reasons mentjoned above, these figures can be taken as minimum estimates.

There'is good agreement between these figures, and the results in Table 9

(based on angler interviews), for the relative contribut'ion made by each acclimatisation district. Approximateìy 50% of the angìers came from hlaitakr

Valley, accounting for 60% of the total effort. 0tago and North Canterbury each accounted for 18% of the ang'lers, who together contributed 28% of the effort.

Most of the remaining anglers came from Ashburton, South Canterbury and Southìand, a'lthough the Ahurirj was noted by two hlellington angìers and one from Auckland.

The figures for total usage - approximately 10 000 visits annually by just under 2000 adult anglers - are meaningful only when compared with usage estimates for other South Island fisheries. In these terms, usage of the Ahuriri falls well below the level of effort associated with rivers such as the blaimakariri, Rakaia, lower l¡laitaki and Mataura, all of which receive in excess of 50 000 visits annua1ly. However, it must be remembered that these rivers are all relatively close to major popu'lation centres, and at least two of them (the Mataura and lower Waitaki) have international reputations as sports fisheries, while the [,laimakarirj and

Rakaja are valued for their salmon fjsheries. The level of usage of the Ahuriri puts it in the top 5% of South Island rivers, and it js reasonable to consider it as a high use river. Consjdering its isolatjon, the popularìty of the Ahuriri can be directly attributed to the hìgh quality of jts fishery.

7.4.5 National importance of the Ahuriri 0f the 160 anglers who fished the Ahuriri, 81 (5M) considered it of exceptìonal ìmportance. Together with the h'igh leve'l of usage it supports, thi s i ndi cates that , 'in terms of the criteria presented jn Appendìx II, the Ahuriri is clearly of national importance (Teirney et al. in prep.).

According to the criteria for both scenic and recreational fisheries, the Ahuriri could equa'lly well fit into either category. The essential features of 58. a recreational fishery - good access, large areas of fÍshable water and high use - are all features of the Ahurjri. These characteristics, together w'ith the exceptional ratings for scenic beauty and sol'itude, also sat'isfy the basic criteria for a scenic fishery. In addjtion, the Ahuriri sustaìns an above-average catch rate, holds large trout, attracts both campers and picnickers, and caters for a wide range of angling techniques. Its largely unmodified catchment, a'lready identified as an asset of prime importance in a regional context, meets another of the necessary conditions for a scenic fishery classification.

TABLE 12. Comparative information about angler usage and importance grades assigned to nationally 'important South Island recreational trout fishing rivers.

Est'imated no . No. of No. Importance respondents of grade Soc i ety of adult Ri ver angl ers from from other soc i ety d'istrìct di stri cts within society soc ì ety Local Vi represented sìt'ing di stri ct dì stricts angl ers angl ers

Upper Nel son 823 36 Bul I er 7 5 4

Motueka Nel son 1058 27 13 5 4

t¡la i tak i Ahuri ri 929 7B 9 5 5+ Val 1 ey

Upper Southern 574 Cl utha Lakes 74 10 5 5 0tago/ Mataura 5110 Southl and 4I I2 5 5

Importance grade 1= not highly valued 5= very hìgh valued 5+= more than 50% of the respondents assìgned an importance rating of 5.

Considering only rivers which are exclusively trout fisheries, the Ahuriri is one of five South Island rivers which satisfy the requjrements for inclusion on our provisìonal list of nationally important recreational fisheries (Tabì e IZ).

Aìthough the Mataura was far more heaviìy fished (it attracted five times more local ang'lers than any other river on the lìst), the Ahuriri attracted more anglers from other acclimatisation districts. If the upper Clutha is excluded (because 59. of major hydroelectríc developments currently taking p'lace), the Ahuriri accounts for almost twice as many vìsiting anglers as any of the other river fisherìes listed in Table !2. The Ahuriri fishery's capac'ity to attract anglers from well outside the Wajtaki Valley region is perhaps the s'ingìe most important factor identifyíng it as a nationa'l'ly important scenic/recreational rjver fishery.

o O. D ISCUSS ION

The Ahuriri River is a moderate-sized river, with h'igh water quality, good spawning gravels and a relatively stable flow regime. The bottom fauna is typically that of a South Island braíded river. Diversìty and dens'ity of species is 'good' with higher values in tributaries, reflecting their greater hydraulic stability relative to the main river. Both diversity and density are indicative of water of high qualìty, with floods providing some restraint on the densities. By way of comparison, the Rakaia R'iver has densities of 170-2800 organisms/mz in the main brajds and 420-3050 jn m'inor braids (FRD unpublished data). Stable, sprìng-fed streams are more productìve, e.g. densities in Boundary Stream, a Rakaía River tributary, ranged from 1640-8090 organìsms/m2 (FRD unpublished data), wh'ile Burnet (1969) recorded values of 3340-8550/m2 from the South Branch of the Waimakariri River.

The Ahuriri tributaries are therefore ìmportant as relatively stable and productive environments for fish, especially juvenìle fish. Also they will contribute signifìcant quantities of 'drift' (i.e. benth'ic 'invertebrates passively or actively moving downstream in the water column - a very important food source for trout) to the main river. Within both the tributaries and main river, food production in various habitats is not uniform and riffles will be more product'ive than pooìs. For instance, l4clay (1968) found invertebrate densities in riffles in the Kakanui River up to Il 327/nz, compared to a maximum of 6 2L0/m2 for pools. Hence the rearing capacity of the Ahuriri River for native fish and trout is intimately linked with the food producing capacity of the system. Any abstractions from the river or its tributaries can be expected to affect riffles 60. in a greater proportion. than poo'ls.

None of the nat'ive fish species recorded is regarded as endangered or uncommon. However, stocks of longfìnned eels have been extensíve1y fished in the South Island, including the upper l,,laitak'i catchment, and there is some concern at the rate of exploitation. Eels are slow growing and longfinned females do not become sexually mature until an average of 34 years of age (Jellyman and Todd 1982). Slow growth, extensive fìshing, and limitations or even complete denial of access, as in the upper lnlajtaki, have all contributed to the marked decline apparent in the populations of longfìnned eels jn South Island high country waters.

The most abundant of the native species, the common buìly, is an important source of food to trout and sockeye salmon in Lake Benmore (E. Graynoth pers. comm.), and no doubtin the lower reaches of the Ahuriri River also. Although trout are catholic jn diet and feed extensjveìy on small invertebrates, ìarger fish are primarily fish eaters. Small forage fish like bullies and koaro, and potentìalìy sockeye salmon, are therefore important links in the food chaíns.

Longfìnned eels over 70 cm are also primarily fish eaters and are dependant upon both native fishes and juvenile salmonids.

The current status of sockeye salmon in New Zealand is cause for concern" At present, New Zealand has the only stocks of sockeye outside their natural range, although the continuance of stocks is seriously threatened by developments in the upper l,rlaitaki power programme.

Sockeye are known to rear and grow rapidly in Lake Benmore. Unti'l recently the majority of the'ir spawn'ing was confined to Larch Stream and simiìar coo'l , clear, sprìng-fed, stable streams at the head of Lake Ohau. If runs are successfulìy established into tributaries of Lake Benmore (which are very different in character, being warm, turbid, and flood-prone), this wjll indicate that the fish could be established in numerous other lakes around the country. If runs fail to develop over the next three to ten years, then these fish would seem to have 'less potential . 61.

In effect FRD's sockeye programme is a large naturaì experiment, caused b¡' the upper l¡la'itaki power development programme. FRD therefore considers it important that efforts be made to protect Benmore tributaries such as the Mary

Burn and 0marama Stream over the next ten years, so that this experiment can be successfu'l 'ly eval uated.

There is also considerable merit in preserving sockeye stocks jn Lake Benmore itself. The fish are occasionally caught by angìers in the lake, but more importantly cou'ld be a source of food for larger trout. l'lature fish ascending the Ahuriri River could also be caught by anglers. Some angìers would obiect to catching these genera'lly smal'l (average about 30 cm) fish, but others would enioy the experience.

The impact of hydro development and further water abstraction on sockeye jn the Ahuriri River and 0marama Stream is clearly very dìfficult to ascertain at the present time. In Omarama Stream, fish were spawning ìn small-sized gravels and jn shallow water. Reductions in water flow and most importantly, increases in water temperature (which are already close to lethal levels for ova) could have serious effects. it is not yet established whether or where the sockeye spawn in the Ahuriri mainstem or tributarjes. In the ma'instem the effects of floods, and in particular bed movement, may limit spawning success and'it is possible that low flows and water temperatures wjll be of relativeìy less importance. However, further studies are needed into these aspects.

From a fisherjes viewpoint, the most important feature of the Ahuriri River is the recreat'ional fìshery based on both brown and rainbow trout" Among the 11 South Island national'ly'important trout river systems identified in the National Rjver Angling Survey (Teirney et al. ìn prep.), the Ahuriri is one of only six rivers whjc.h provide a mìxed brown trout/rainbow trout fishery. The other five rìver systems are all located'in Southland and the Southern Lakes Conservancy.

Brown trout dominate the river fishery, constituting 64% of the anglers' catch. Similar proportions of brown:rainbow trout occurred in the samples of 62. juvenile trout (6S% brown trout,35% rainbow trout, n = 586). Although it might seem reasonable to interpret these data as indicating that constant proport'ions of each species (juvenile to adults) are resident in the ríver system, consideration of further data suggest this is not so.

It 'is generally accepted that where both species co-exist, angìers catch a significantly smaller proportion of the available brown trout than they do of rainbow trout (Bursta'll 1975). For instance, in Lake Benmore, anglers' catches from 1969-1981 (n = 5994) were 417á brown trout and 59% rainbow trout (FRD unpublished data). However, trout sampled from gì.l1 and seine nets in Lake Benmore 1975-1981 (n = 1323) showed a relatively hìgher proportion of brown trout (65%) and a correspondingly lower proportìon of rainbow trout (35%) (FRD unpublished data). The latter data are regarded as a more accurate reflection of the species proportìons than the anglers' catch.

0n this basìs, it would be antic'ipated that adult brown trout should occur in the Ahuriri River ìn a relatìvely h'igher proportion than ind'icated by anglers' catches. However, the s'ituation is further comp'licated by indications in the data of seasonal differences in behaviour between the two species - brown trout tend to be res'ident within the river, while rainbows appear to be more mobile, living mostly in Lake Benmore and moving into the Ahuriri durìng late summer. Support for this view comes from several observations: movements of tagged fjsh, species proportions observed in drift d'iving, seasonal differences jn the species proport'ion of trout caught by anglers and observations of shoals of adult fish (species unknown) off the river mouth and in pools'in the lower river in March.

In addition, the Tekapo River trap data show upstream migrations of rainbows occur well in advance of the spawn'ing season, while drift d'iving counts in the

Rangit'ikei Rjver showed seasonal differences in ra'inbow trout densities (g-¡S rainbow trout/km compared to B-19 brown trout/km) cons'istent with seasonal migrations (Hjcks 1982).

If the above postulation is correct, then'it js ìikely that brown and ra'inbow 63. trout spawn in the Ahuriri River in simiìar proport'ions to the iuvenì1e sampìing data, i.e. 65% brown trout: 35% rainbow. However, relatively higher numbers of brown trout juveniles take up residence jn the river and tributaries than do rainbows. This may be due to brown trout fry hatching earìier and taking up terrjtories, thus forcing many ra'inbow fry to migrate downstream into Lake Benmore' or, raìnbows may have a preference for lake-dwell'ing and iuveni'les may m'igrate volunta¡i'ly. Either way, brown trout make up the larger proportìon of resident fish jn the river, while large numbers of rainbows from Lake Benmore move into the lower reaches several months in advance of spawning.

Table 13 gives the mean lengths of brown trout and rainbow trout for high'ly regarded South Island river fisheries, plus data from Lake Benmore. The Ahuriri

River shows up very favourably, having the largest mean size of rainbow trout and being second to the upper Pomahaka for sjze of brown trout. The Pomahaka'is regarded as a trophy trout fishery, typified by large sea-run fish but low rate of catch. The fact that the Ahurirj d'id not rate exceptionaìly highly in the National River Angling Survey for catch rate and size of fish is more a reflection of anglers'conservat'ism than the state of the fishery - anglers never seem to regard these qual'it'ies as attaining h'igh enough values.

Catch rate in the Ahuriri River exceeded those of other rivers listed in Table 13, but was less than that for Lake Benmore, particularly the Ahuriri Arm.

Lake Benmore is well known as a high'ly product'ive fìshery and fishing js both shore and boat based. Although the lake comprises two arms, the North Arm and the Ahuri¡i Arm, tag return data (FRD unpublished data) indicate that both arms maintain somewhat discrete and separate fish stocks. Hence the angìing potentiaì of the Ahuriri Arm'is dependant upon the spawnìng of trout in the Ahurjri River.

Any deterioration of spawn'ing or juvenile rearing conditions in the Ahuriri River, either qual'itative or quantìtative, could serious'ly downgrade the quality of angling in both the river itself and the Ahuriri Arm of Lake Benmore.

FRD's National River Angling Survey has provided informat'ion on 430 South

Island ¡ivers, and the regional importance of the Ahuriri River fishery has been 64.

TABLE 13. Comparative anglìng data for some South Island trout fisherjes.

Mean Length lo lo * Data Ri ver Date F'ish/hr empt.v Brown Ra i nbow returned sou rce Trout Trout bag s

Ahuri ri Thi s Rì ver t962-82 0.31 47 2 42.6 49 23 study

Lower Wa'itaki 1973-75 0. 11 45. B 37. B 77 I

Mataura t976-79 0. 15 44.0 76 ï

Upper Pomahaka 1976-80 0.09 52 5 B1 27 1

Lower Pomahaka 1973-80 0. 18 40 0 74 30 T

Lower Ta i eri I973-77 0. 13 36.0 85 33 1

Waikaia 1977 -80 0.26 4t.6 B2 23 1

Lake Benmore (Ahuri ri Arm) 1980-81 0.69 40 7 39.3 2

Lake Benmore t969-73 0.47 44 I 34.3 2,3

* Data source: 1 = 0tago Acclimatisation Socìety Annual Report (1980) 2 - Thornton and Stancliff (In press) 3 = Gra.ynoth (1975) 65.

established (Teirney, Richardson and Unwin t982). However, FRD's national survey has also shown the Ahuriri to be a nationally important rìver; it is one of the few South Island river fisheries which qualífied on all counts for inclus'ion in both the nationally important scenic and recreational categories. Among the nationalìy important trout fishing rivers, the Mataura (a fishery of "international reputation) is most heavily fished, but the Ahuriri attracts the highest number of anglers from other acclimatisation districts. If the upper Clutha is excluded because of major hydro-eìectric development modifications which

are to take p'lace in the near future, then the l4ataura and Ahuriri also share the highest ìmportance grades awarded by both local and visiting anglers. In addìtion, analysis of ang'ler diarjes and interviews has shown the Ahuriri to be a valuable river fishery for both size of fish and catch rate, with brown and rainbow trout both available to anglers.

Other important attributes are the good access along virtually the entire ìength of the river, the opportunit'ies for picnicking and camp'ing in association

with angling, and the high scenic value of the area above the gorge. It has been w'idely recognised and now confirmed by FRD's national survey, that the angling experìence is at least as important to anglers as ang'ling success. Anglers are willing to expend considerable time, effort and expense to travel to the Ahuriri because it offers excel'lent angling in scenic surroundings.

Most fishing occurs close to Omarama, which is within easy reach of people holidaying ìn the Benmore area. The presence of significant numbers of junior anglers encountered during the surveys, as well as a high proportion of threadline anglers, ìs a good indication that the river has wide appeal to families (spinning

is a less-skilled form of angling than fly fishing). However, for the more devoted angler, the river also affords quaìity fishing within areas rated highly in terms of scenic beauty and feel'ings of solitude.

Several reasons can be put forward for the high fisheries productivity of

the river. The river arises within a partially forested catchment. Hence runoff 66.

ìs regulated by the interception of vegetation and the catchment'is physically stable. Silt loads are correspond'ingìy low and there is no 'flour'characteristjc of glacier-fed rivers. The flow regime is relatively stable wjth sufficient floods and freshes to flush any sed'iments from the spawning gravels and riffles' and also frequent enough to act as a stimulus to upstream migrating fish. However, the floods are seldom of such a magnitude as to cause significant bed-load movement and so seriously impair invertebrate product'ion and downgrade fjsh hab'itats. In addition, Lake Benmore prov'ides a reservoir of fish which, no doubt' serves to repopulate the Ahurirj as habitat becomes available.

A'lthough summer flows in the middle and lower reaches are already affected to some extent by existing abstract'ions, flows seem to be adequate at present to maintain water of sufficient quaììty and quantity to provide for fisheries requirements. Assessment of the impact of specifíc add'itional abstractions is both complex and time consuming and beyond the scope of this report. Factors' affecting fish hab'itat, their relationship w'ith flow and comment on methods for assessìng impacts of reduced flows on fish are contajned in Appendix III. There is little doubt that addjtional abstractions from the Ahuriri would signifìcantly downgrade the fjshery value of the river. For jnstance, a reduction in the number of side braids would result in less rearing area and less food production, while an'increase in flat water surfaces would decrease the amount of instream cover available to fish. However, jn the absence of a specific study, these factors cannot be quantified.

The National Executive of New Zealand Acclimatisation Soc'ieties has indicated their intent to apply for a Nat'ional Conservation Order for the Ahuriri River

(under the 1981 amendment to the l^later and Soil Conservation Act), on the basis of the river's fisheries and wildlife values. It is understood that the t¡lildlife Service of the Department of Internal Affa'irs also intends to apply.

l,lith the continu'ing development of New Zealand waterways for irrigat'ion and hydro-electrjc power generation, the opportunity for ang'lìng in unmod'ified 67. rívers is becoming increasingly scarce. Several prime South Island angìing rivers are already extensively modif ied, including the Wa'itaki, Clutha and l¡laiau, while development proposals on others are be'ing considered. As stated previous'ly, the Ahuriri River is the only major relatìve'ly unmodified river fìshery in the upper ÌnJaitaki catchment. This factor, combined with its outstandìng fisheries qualities, gives'it a ranking among the top few South Island fishing rivers - on the basis of some criteria, it'is the most ìmportant South Island river.

9. CONCLUS IONS

With the except.ìon of the Ahuriri River, the rivers of importance to fisheries within the upper Waitaki catchment are high]y modified. Consequently, the fishe¡ies values of these rivers has been reduced, resulting in an increase'in importance of the Ahuriri fishery.

The Ahuriri Rjver supports a trout fishery of national 'importance to anglers and is one of only two prime spawning tributaries for fish from Lake Benmore. (Trout from the t\orth Arm of Lake Benmore spawn ìn the Tekapo River and tributaries, while trout 'in the Ahuriri Arm use the Ahuriri.)

Thus, it seems appropriate to reta'in the Ahuriri River in its present state for the purposes of recreation and preservation of natural values. Accordingly,

FRD recommends that no further allocation of the water resource be permitted.

This recommendation is made on the basjs of a quaììtative assessment that the fjsheries values of the Ahuriri R'iver are such that further partitioning of the water resource is not warranted.

10. SUMIVIARY

1. The Ahuriri River flows into the Ahuriri Arm of Lake Benmore and i s the last major, relatively unmodified river fi shery in the upper Waitaki

catchment. 68.

2. The fìsh resource of the Ahuriri River comprises five native species and three introduced salmonids. The presence of sockeye salmon is of interest as stocks in the Waitaki catchment represent the only popu'lation outside the'ir natural range.

3. The Ahuriri R'iver supports a recreational fishery based on stocks of both brown and rainbow trout, w'ith brown trout comprìslng 64% of anglers' catches.

4. There is considerable movement of both trout species between Lake Benmore and the Ahuriri River, representing a migratory populatjon of fish moving into the river to feed and/or spawn, and a population of river fish. Trout popuìat'ions in the Ahuriri Arm of Lake Benmore are dependent on the Ahuriri

River for spawning.

5. Most trout spawning occurs in two reaches of the Ahurjri - upstream of the gorge, and downstream of Clay Cliffs - and in some of the tributaries -

Omarama Stream, Djadem Stream, Longslip Creek, Hen Burn and Quail Burn.

6. The Ahuriri River is fished by anglers from many parts of New Zealand, as

wel I as by some overseas tourists. Visit'ing anglers represent approximately

50% of the anglers fishing the river.

7. Estimates from FRD's Nat'ional River Ang'ling Survey jndicate that the Ahuriri River is fished by just under 2000 adults, who make approximately 10,000 vis jts annual'ly.

8. The most heav'ily fished reach of the Ahuriri R'iver is the area downstream of Diadem Gorqe.

9. Data from FRD's natjonal survey indicate that the Ahuriri River is valued for its scenic beauty, ease of access, peace and solitude. Visit'ing anglers cons'idered the catch rate and size of fish to be well above average, particularly in the upper reaches. 69.

10. The Ahuriri River has been identified as a mixed brown/rainbow trout fishery of national ìmportance. It qual'ifies under both 'scenic' and 'recreational' criteria, for inclusion in FRD's submiss'ion to the National Water ancl Soil Conservation Authority on wild and scenic rivers of nati onal 'importance.

11. FRD recommends that the Ahuriri River is retained in its present state and that no further abstraction of water is permitted.

11. FURTHER INFORMATION REQUIRED

Th.is section seeks to identify areas where further ínformation is required for a comprehensìve assessment of the Ahuriri River resource, clarification of which should be a pre-requisite to any further allocat'ion of the water resource for any out-of-r'iver use.

1. Fi sheries Information. Further sampling in selected habÍtats'is required to add to existing, limited information on the djstribution and abundance of the various fish species within the catchment. This should include:

(a) Quant'itative samp'lìng of specìf ic habitat types within the main river (particularly in the area that would be affected by the proposed abstraction), to determine the relat'ive importance of runs and riffles

for juvenj I e fi sh .

(b) Further drift divìng counts of trout to confirm seasonal movements.

(c) Further angfing interviews to record catch/effort statistics, areas

f i shed, s'ize and spec'ies of f i sh , etc.

(d) A generaì assessment of recreat'ional use of the Ahurjri catchment.

(e) Analysis of data on the movements of fish'in Lake Benmore is requìred, jn to prov'ide a better understancling of the separatjon of trout stocks

both arms of the lake, relative to the Ahurjri River population. 70.

A fìeld orogramme to collect some of these data has commenced. However, because of constrajnts of time, staff and expert'ise, FRD is not ìn a posit'ion at present to carry out a fish habitat use survey and associated studjes, to attempt pred'ict'ion of the specìfic effects of a particular

abstracti on .

predi cti ve model s and methods are sti I I bei ng devel oped overseas . I'J'ithi n

New Zealand, FRD has major studies in progress on the Rakaia and lower Waitaki Rivers. An evaluation of the merits of the various methods and their applicability to New Zealand fresh waters, such as the Ahurjri, would be difficult, and probab'ly inadequate, unti'l completion of the ltlaitaki and Rakaia studies.

2 . t^J'i I dl 'ife Informati on . The value of the Ahurirj River system as a wildljfe habitat for several endemic bird species is currently being ascertained by the Wildlife Service of Department of Internal Affairs. Time should be allowed for their studies to be completed and ana'lysed, so that the'importance of the Ahuriri as a wildlìfe habitat can be evaluated.

3 . Hydroì ogy. A model of changes to the flow regime of the Ahurìrj River as a result of the proposed 4 m3/s abstraction is required. In particular, the effect on low flow years and on the flow duration curve should be documented.

4. Water Temperature. Continuous monitoring of water temperatures, particular'ly over the summer period, would be desirable.

5. Irrigation. Given the high fishery and recreational values of the Ahuriri River, emphasis should be on investigation of alternative sources of water supply for ìrrigat'ion, especially since water from within the upper Waitaki power

scheme has been designated for this purpose. If irrigation development 7r.

is to be encouraged ìn the Mackenzie Basin then'it should be on an integrated and well researched basis, jncluding an adequate economic assessment of

al ternati ves .

12. ACKNOWLEDGEMENTS

The authors sincerely thank Eric Graynoth for providing his unpub'lished data on sockeye salmon and commenting on the draft manuscript; Martin Unwin for assjstance wjth the l{ational River Angling Survey data analysis; and Chris Kime for drafting the figures. Staff from the Waitaki Valley Acclimatisation Society and fjsheries consultants employed on the upper Waitaki, assisted with field work.

13. LITERATURE CITED

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Burnet, A.M.R. 1969. A study of the'inter-relation between eels and trout, the invertebrate fauna and the feeding habits of the fish. N.Z. Þlarine Department, F'isheries Technical Report No. 36. 23 pp.

Burstal'l , P.J. 1975. Sport fisheries. pp. 308-318. In: Jolly, V.H. and Brown, J.M.A. (Eds. ) New Zealand Lakes. Auckland University Press, Auckland. 3BB pp.

Cadwallader, P.L.1976. Home range and movements of the common river ga'laxias, Gafaxias vuJsaris Stokell (Pìsces: Salmoniformes), 'in the Glentui River,

New Zealand. Australian Journal of Marine and Freshwater Researcì ?l-0): 23-33. 72.

Cadwallader, P.L. 1978. Age, growth and cond'it'ion of the common river gaìaxias,

Gal-axias vurgaris Stokell, in the Glentui River, Canterbury, New Zealand.

Bulletin No. L7. 35 pp.

Campbeì1, R.N.B., Rjmmer, D.M., Scott, D. and Shirvell, C.S. In press. The effects of reduced discharge on trout in small New Zealand streams. Paper presented at 2nd International Symposium on Regu'lated Streams, Un'iversity of Oslo, Norway, B-I2 August t982.

Davis, S.F. 1982. Hurunui angler survey. Freshwater Catch No. 5-6.

Egarr, G.D. and Egarr, J.H. 1981. New Zealand recreational rlver survey.

Part III. Summaries of South island rivers. Water and Soil Miscellaneous

Publìcation No. 15. 160 pp.

European Inland Fisherjes Advisory Commission. 7964. I,Jater quality criteria for European freshwater fish. Report on finely div'ided solids and inland fisheries. European Inland Fisheries Advisory Commìssion Technjcal Paper No. 1. 21 pp.

Flain, frl. 1971. Sockeye salmon oncorhsnchus nerka (hlalbaum). Wajtaki Valley Acclimatisat'ion Societv Annual Report l97I: 20-21.

Foerster, R.E. 1968. The sockeye salmon oncorhqnchus nerka. Bulletin of the Fisheries Research Board of Canada 162. 422 pp.

Gabites Porter and Partners. 1982. Waitaki water and so'il resource management

plan. Volume 2. Description of the Waitakj catchment. Report for

Waitak'i Catchment Commission and Regjonal Water Board. 206 pp, plus

appendix and references.

Graynoth, E. 1974. New Zealand angling 1947 - 1968. An assessment of the nat'ional angf ing d'iary and posta"l questionnaire schemes. l{.2. Ministr-y . 7o pp. 73.

Graynoth, E. 1975. Brown and rainbow trout in two New Zealand hydroelectric lakes. Unpubl ished report, Fisheries Research Dìvis'ion, M'inistry of 'l Agri cul ture and Fi sheri es , Inlel i ngton . 38 PP , Pl us f i gs and tabl es .

Graynoth, E. 1978a. Sockeye salmon and the upper l'lajtaki power scheme. Report to Minjstry of Works and Development, New Zealand Electricity and Accljmatisation Societies by Fisheries Research Divjsion, Minjstry of Agricu'lture and Fisheries, Christchurch. 28 pp.

Graynoth, E. 1978b. How to identify and catch sockeye salmon. Waitak'i Valley Acclimatisation Society Annual Report 1978: 35-37.

Graynoth, E. Ig7g. Sockeye rescue proceeding smoothìy. Freshwater Catch No.4: 6-7.

Graynoth, E., Pierce, L.A. and Wing, S.J. 1981. Fisheries aspects of the lower Waitaki power scheme: An assessment of the impact of various development options on the fish stocks and fisheries. and Fisheries, Fisheries Environmental Report No. B. 72 pp.

Graynoth, E. and Skrzynski, W. 1973. The Waitaki Valley trout and salmon fishery.

N. Z. Mini stry of Aqricul ture and F j sheries, Fi sheries Technica] IgppI!--Ng.-lQ!-.

36 PP'

Hardy, C.J. 1969. Unexpected appearance of an uncommon freshwater fish.

Waitaki Val I e.v Accl imat'isatìon Soc'iety Annual Report 1969: 29-30.

Hawke, L.J . L982. Operat'ion: save the sockeye! Freshwater Catch No. 16: 14.

Hewson, J.|.4. 1982. Waitaki Lakes Recreation Survey, Christmas 1981. Report to Waitaki Joint Planning Comm'ittee, ldaimate. Unpaged.

Hi cks , B .J . 1979. Rang'i t'ikei Ri ver f i shery ieopardi sed. Fr"eshwater Catch No.4z 16.

Hicks, B.J. L982. Rangitikei River survey update. Freshwater Catch No. 14: 8-9. 74.

Hobbs, D.F. 1948. Trout fisheries in New Zealand: Their development and management. N.Z. Irlarine Department, Fisheries Bulletin I'10.9. 175 pp.

Jellyman, D.J. In preparat'ion. The djet of freshwater eelS AnsuiTTa spp. 'in

a small New Zealand lake.

Jel]yman, D.J. and Todd, P.R. 1982. New Zealand freshwater eels: Their bìology and fishery. N.Z. ['linistry of Agriculture and Fisheries, Fisheries Research Division Information Leaflet No. 11. 19 pp.

Jowett, I.G. 1978. Upper hlaitaki power development and fisherjes. Report to Power Dìvision, Ministry of Works and Development, lrjellington. 18 pp, plus

maps.

Kerr, I.G.C. tg7g. Potential minor and major irrigat'ion schemes upper Waitaki Catchment. Appendix 4. pp. 194-?09. IN: Whìtby, M.C. Economics of Pastoral Development in the Upper Wa'itaki. N.Z. Man and the Biosphere Report No. 3. Tussock Grasslands and l4ountain Lands Institute, Ljncoln

Col I ege . 220 pp.

McDowall, R.t4. !978. New Zealand Freshwater F'ishes - A Guide and Natural

Hi story. Hei nemann , Auckl and. 230 pp.

Mclay, C.L. 1968. A study of drift'in the Kakanui River, New Zealand. Australian Journal of Marine and Freshwater Research 19: 139-149.

Mi ni stry of hlorks and Devel opment. 1980. Revì ew of l,'lai tak'i hydrol ogy. 104 pp '

p1 us appendix I II.

Ministry of Works and Development. 1981. Ahuriri R'iver at South Diadem. Da'i1y

means 1,970-1982. TIDEDA, 7/9/82.

I'losìey, M.P. 1982. Physìcal character of the Ahuriri River. Internal report

No. WS 633, l,later and So'il Division, 11ìnìstry of Works and Development, Christchurch. 15 pp, plus tables and figs. 75.

National Water and Soil Conservation Organ'isation. 1982. A draft for a national inventory of wild and scenic rivers. Part I - Nationally important rivers. l¡later and Soil Miscellaneous Publication N0.42. 64 pp. 0'Connor,K.F.I976.AnintroductiontotheWaitaki.N.Z.M@ Report No. 1. 90 pp.

Reid, C.J. 1982. 0hau-0marama basjn jrrigation. Internal report, M'inistry of

Works and Development, Dunedin. 4 pp, plus map.

Richardsoh, J.and Teirney, L.D. 1982. The Whakapapa River: A study of a trout fishery under a modifjed flow regime. N.Z. Ministry of Agriculture and Fisheries, Fisheries Environmental Report No. 22. 71 pp.

Robinson, A.W. and Hall, R.J. 1982. Ahuriri River - water right appl'ication 598. Submission to meeting of objectors/applicants on 25 August 1982, Waitaki

Catchment Commission and Regional Water Board. 4 PP, Plus appendix.

Royds, Sutherìand, Mcleay Ltd. 1982. Small Hydro-electric Potential of the Waitaki Electric Power Board District. 35 pp, Plus appendices.

Scott, W.B. and Crossman, E.J. 1973. Freshwater fishes of Canada. Bulletin of the Fisheries Research Board of Canada 184. 966 pp.

Shirvell, C.S. and Scott, D. In press. The effects of reduced discharge on temperature and dissolved oxygen in Deep Stream, 0tago. Paper presented

at 2nd International Symposìum on Reguìated Streams, University of Oslo,

Norway, 8-I2 August 1982.

Stokell, G. L962. Pacifjc Salmon in New Zealand. Transact'ions of the Royal

Soc'iety of New Zealand Zoology Z (Zt)t 181-190.

Te'irney, L.D. 1979. The ups and downs of drjft diving. Freshwater Catch l{o. 4:

12-13.

Teirney, L.D. 1982. Instream Flow Group (IFG). Freshwater Catch No. 14: 11-14. 76.

Teirney,1.D., Richardson, J. and Unwìn, M.J. 1982. The relative value of |,rJaitaki Valley rìvers to l,Jaitakj Valley anglers: A prel iminary report.

No. 19. 46 pp.

Teirney, L.D. et al. In preparat'ion. Submissìon on the draft inventory of of wild and scenic rivers of natjonal ìmportance. N.Z. l!.Uslfy-of

Thomson, G.14. 1922. The Naturalisation of Animals and Plants'in New Zealand. Univers'ity Press, Cambridge. 607 pp.

Thornton, B.K.and Stancliff, A.G. In press. Angling in the upper Waitaki catch- ment 1980/81 season. N.Z. Ministry of Agriculture and F'isheries, Fisheries

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Unwin, M.J. 1980. Rakaia angler survey. Fre¡hwater Catch No. 6: 9-10.

Unwin, M.J. 1981. Rakaia angler survey. Freshwater Catch No. L2: 3-4.

t,rlaitaki Regional Water Board. I975. Prel'iminary water allocation plan for Mackenzie-Omarama district. 12 pp, plus appendices.

l,rlaitak'i Regional l,rJater Board. L977. The resourc,es and usage of water in the

l4ackenz'ie-Omarama district. lrja'itaki Regionaì Water Board, Kurow. 29 pp,

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act'ions of the American Fisheries Society 90: 225-226.

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No. 6. 10 pp. 77.

APPENDIX I. Angler interview form.

MINISTRY OF AGRICULTURE AND FISHERIES

SURVEY WATER ZONE olt c D E F

D AM AM PM PM

DATE TIME DAY

LICENCE NO. KIND M W J CATEGORY hls M Ì^J D

LICENCE DISTRICT A SC I^lV NC HOME

INTERVIEWED BEFORE TACKLE T/L D/F w/F l^l T

FISHING FOR TROUT I SALMON PREFER

6AM 1zAM 6PM 12PM TOTAL TIME 25 50 75 100 FISHING HOURS

CATCH TROUT SALMON TOTAL BOAT I SHORE

BROt^JN RAINBOI^J QU I NNAT

COMMENT

OBSERVER 78.

APPENDIX II. Classjfication of river fisheries of national importance"

To jdentify rivers of national ìmportance, a two stage classjfication system

has been developed, based on the survey results (Teirney et al. ìn prep.). Firstly, r'ivers were assessed in terms of their overall importance (based on the anglers'1-5 ratings), as to whether they were sufficiently highly valued to be considered of national 'importance. Secondly, rivers thus selected were placed 'into one of three categories, accord'ing to how their varìous attributes (ease of access, scenic beauty etc.) were rated.

In terms of the overall importance ratings, r'ivers generally were considered further only if a ratjng of 5 (exceptional ) was the most frequent'ly awarded by ang'lers who had fished that river. For rivers supporting a h'igh level of usage,

th'is was usually the only quaì jfjcation considered necessary. For rivers with lower usage, a s'lightly stricter requìrement was adopted, in that an exceptional

rating had to be given by at least 50% of the respondents. Inevitably this

process produced some borderline cases, but in general 'it was possible to make clear-cut decisions as to the importance of a particular river fishery.

The three sub-categories of natjonally important river fisheries which were identified were defined as wilderness fisheries, scenic fisheries and recreational fisheries. All rivers cons'idered to be national'ly important were assigned to one (or occasionally two) of these categorìes. The defining crìteria for each of these three categorìes are listed in Table 14.

Wilderness fisheries were characterised by remoteness from population centres, lack of road access, and unmodified catchments. As a result, these rivers recejved exceptìonally hìgh ratìngs for the opportunity of fishing in peace and solitude, and scenic beauty. South Island rivers such as the Sabine, Travers, Hunter and Greenstone were included in this category.

Scen'ic fisheries shared some of the characteristics of wilderness fisheries, in that they were generally remote from population centres and received exceptional 79.

TABLE 14. Criteria used to classìfy national'ly important South Island river fisheries into w'ilderness, scenic and recreatjonal categories.

1. t,.lilderness river fisherjes generally share the following characteristics: They are remote from population centres. They are not accessible by road. They are not fi shed by a I arge number of angl ers. Access to the river is not considered to be easy. Areas of fishable water are extensive. Scenic beauty and solitude are considered to be exceptional. The catch rate is relat'ively high. The river contains reasonably large trout. Anglers prefer to use artificial flies. Camping, tramping and shoot'ing are often associated with fishìng. Any catchment modifications are of a minor nature only.

2. Scenic river fìsheries generally share the following characteristics: They are usually, but not necessarily, remote from population centres. They are accessible by road. They may attract a ìarge number of anglers. Areas of fishable water are extensive. Scen'ic beauty and sol'itude may be as highly valued as for wilderness físheries. Catch rate and size of fish ratings may not be qu'ite as high as for wilderness fi sheri es . Spinning may be as popuìar as artifjcial flies w'ith anglers. Camping and picnicking are often associated with fishing. Modifications to the catchment or river may have occurred, but these are not of a major nature.

3. Recreatjonal river fisheries general'ly share the follow'ing characteristics: They may be close to population centres. They are easì'ly accessibl e by road. They attract a large number of anglers. They attract visiting anglers from well beyond the local area. Areas of fishable water are extensive. Scenic beauty and solitude are not necessarily high. The river supports a h'igh catch rate and/or holds large fish. Spinning is often the preferred angling method. Picnicking ìs most commonly assoc'iated with fishing. Relatively major modifìcations may have occurred to the catchment or river. 80. ratings for scen.ic beauty and solitude. However, they were usually accessible by road, and were therefore more heavily fished than wilderness rivers. Some catchment modificatìon (e.g.farming) was acceptable, provided that'it did not detract from the scenic attributes of the catchment. South Island rivers which fjtted into this category included the Maruia, upper Hurunui and Eglinton.

Recreational fisheries were characterised above all else, by high use, both from within and outside the local acclimatisation soc'iety d'istrict. Access to these rivers was good, and they were often close to major population centres. Scenic beauty and solitude were not necessarily highly rated. All four major

salmon fisheries in the South Island (the I'laimakariri, Rakaia, Rangìtata and lower Waitaki) were included in this category, ôS were the l4ataura and Motueka

Ri vers . 81.

APPENDIX III. Factors affecting fish habitat, and their relatjonship with di scharge.

The natural flow regime whjch charactenises the Ahurirj River is a consequence of the combìned influences of climate, geographic location and certain catchment features. This flow regime profoundly affects the habitat of those fish species which complete either a part, or alì, of their life cyc'le within the river.

Su'itable fish habitat is created by a compìex 'interaction between phys'ical , chemical and b'io'logical factors, each of whjch may be affected either direct'ly or indirectly by the pattern of flow fluctuations. As a result, the fish stocks and fishery values currently supported by the Ahuriri River are adapted to, and dependent upon, the existing flow regìme. Any manipulation of this flow regime therefore has the potent'ial to alter fish habitat and fishery values associated with the river.

The following generalised discussion is provided to highl'ight the subtle and complex ways in which a reduction'in flow associated w'ith the abstraction of water during summer months, ffiô.y alter various aspects of fish hab'itat. Wh'ile the list of poss'ible effects'is by no means exhaustjve, jt does reflect a growing body of knowledge and experience of the New Zealand situat'ion.

Abstraction of water from the Ahuriri would lower the base flow which characterises the rjver, downstream of any intake. Although the natural pattern of flow fluctuat'ions would not be altered, the magnìtude of these fluctuations would be increased. Results from a recent investigation into the effects of water abstraction from the Whakapapa River, forinstance, suggest that this type of hab'itat destablisation has contrìbuted to a reduction'in trout stocks of up to

90% downstream of the jntake (Richardson and Teirney L982).

Reduction in summer flows is unlikely to affect the way in which sediment is moved through the Ahuriri River system ìn a major way, because the majority of sediment is transported during f'lood events. However, the accumulation of fjne sediments on the substrate will increase during prolonged perìods of low flow. Among the effects this may have on trout habitat is a possible alteration. 82. in the spec'ies composition, density or availability of the benthic invertebrate fauna, a maior component 'in the diet of trout.

Further , there 'i s the possi b'il i ty of increased al gal and peri phyton growth , as occurred in the Qpu'iaki Rìver following divers'ion of water for hydro-electrjc generation in the Lloyd Mandeno Scheme (Bioresearches Ltd. pers. comm.), and in the Qhau River jn February 1980, following diversion of water (E. Graynoth pers. comm.). Llhile thjs may result in an increase in dissolved oxygen concentration du¡ing the day, the combination of alga'l respiration anci decomposition of additional organic material can lower the concentration of dissolved oxygen at nìght. In low velocity areas, such as occur at the bottom of poo'ls, dissolved oxygen may be substantially reduced (Shirvell and Scott in press). As a result, those species which cannot tolerate such condjt'ions are excluded from these areas.

Although water temperature is highly correlated with the prevaì'ling meterolog'ica1 cond'itions, an inverse relationship also exists between water temperature and d'ischarge during the warmer months. Therefore water temperature js likely to be elevated by the abstraction of water from a rjver during summer. While water temperature may not exceed the optimum range of various fish spec'ies, an increase in temperature ra'ises the metabol ic rate and associated oxygen requirement of fish, with the result that growth rates may be depressed. Conditions of stress, such as those which may be imposed by an elevation in water temperature or a deplet'ion of oxygen, tend also to increase the susceptabìlity of fish popul ati ons to di sease.

Another component of fish habjtat which p'lays a vital role'in the maintenance of existing fish communities, and whìch may be altered by a lowering of summer flows, is cover. In a rÍver like the Ahuriri, fish may gain a measure of protection from a range of predators by utilising the ìnstream cover provìded by boulders, cobbles, surface water turbulence and depth. Drift diving observatjons 'in the Manganui-a-te-Ao River have revealed, for instance, the importance of surface turbulence in riv.ers where riparian cover plays only a mjnor role" A reduction 83.

ìn this type of instream cover is ljkely to be associated with lower flows.

As a result of habitat modifications caused by reduced flows, behavioural 'interactions within the fish community (at both an intra- and inter-specific level) may undergo certain changes. For instance Campbell et al. ('in press) found that as the velocity decreased in S'ilverstream, territorial behaviour exhibited by resident juvenile trout was d'isrupted and replaced by shoaling behaviour.

Should this type of response be triggered by reducing summer flows in the Ahuriri,

trout could be lost to the river through out-migration to Lake Benmore.

The need to quantify such a range of inter-related effects has been promoted recently because of proposals to use the water resources of the Ahuriri for out-of- stream purposes. However, the appìicat'ion of recently developed methodologies such as the Instream Flow Incremental Methodology (IFIM) (U.S.Fish and l,Jildljfe, Instream Flow Group), can only provide guidance on selected physical aspects of

fish habitat. Certain limjtations are also imposed by some of the assumptìons

upon which this methodo'logy'is based, and these have been summarised by Teirney

(i982). However, the fact that a relationship has yet to be demonstrated between the measure of physical hab'itat resul tìng from the IFIM, tdeighted Usable Area,

and fish stocks or production in New Zealand rivers and streams,'is perhaps the most serious limitat'ion of this method. For this reason, caution must be exercised in the interpretation of data collected according to this type of methodology.

In response to the recent'irrigatìon proposals, the Mìnìstry of Works and Development conducted an investigation 'into the impact which water abstraction

might have on the physical character of the Ahuriri Rjver (l4os'ley 1982). The interpretation of data was extended to include predìctìons about the effects which these physical changes were likely to have on the fishery values supported by the river. Mosley concluded that an accurate predictjon of the'impacts of water abstraction is unlikely in the short term because of the inherent compìexity which characterises the relationships between habitat, fish stocksrproduct'ion and fishery values, and the lack of sujtable predìctive methodologies. To satisfy the 84. t data requi-rements, a major investment of resources would have to occur over a consjderable period of time. I Those physical aspects of fish habjtat dealt with by Mosley (1982) however, I consistently indicate that a lowering of the flow in the Ahuriri is likely to adversely affect a range of existing physicaì habitat valués. Assuming that the I fish populations are determined to some degree by available physìca1 habitat, abstraction of water could therefore cause a reduction'in the fish stocks and associated fishery values.