The Ahuriri River System
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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).