FISH AND FISHERY VALUES OF THE RAKAIA RIVER: A PRELIMINARY RTPORT BY SALLY DAVIS FISHERIES ENVIRONMENTAL REPORT NO. 2 N.Z. MINISTRY OF AGRICULTURE AND FISHERIES CHRI STCHURCH SEPTEMBER r979 FISI.IERIES ENV IRONMENTAL REPORTS 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 wi thout the author's permission. (2) They are for limited circulation so that persons and organisations normally receiving Fisheries Research Division publications should not expect to rece'ive copies automatica'11y. (3) Copies will be issued in'itia'lly to organisations to which the report is directly relevant. (4) Copies wiì1 be issued to other appropriate organisations on request to Fisheries Research Division, Ministry of Agriculture and Fisheries, Private Bag, Christchurch. (5) Tl.re¡e reports wì1.l be issued where a substantial report is requìred with a time constraint, e.g. a submission for a tribunal hearing. (6) They wi'll also be issued as interim reports of on-goìng environmental studies for which year by year or intermittent reporting is advant- ageous. These interim reports will not preclude formal scientific pub'licatjon. CONTENTS Pàge 1. Introduction 1 2. Fish Resource 2 2.7 Native Fish 2 2"L"7 Migratory SpecÍes 4 (i) Estuarine specìes 4 Rhombosofea retiaria 4 GaJaxias macuLatus 4 (ii ) Lower river resjdents 5 Retropinna retropinna 5 Stokel-l-ia anisodon 6 Gobiomo rphus cotidjanus 6 (iii) 0thers 7 Geotria aust,ral-is 7 AnguiJJa dieffenbachjj ônd A. austral-is 9 Gafaxias brevipinnis 10 Cheimar richthg s fosteri 11 Gobiomorphus hubbsi 72 2.7.2 Non-Migratory Species 12 Gal-axias vulgaris I2 GaL ax i as pauci spondg Jus 13 GaLaxias prognathus 13 Gobiomorphus breviceps 13 2.2 Introduced Fi sh L4 Oncorhgnchus t shawgtscha t4 SaTmo gairdnerii ?I Sal-mo trutta 2T Sal-veJ- inus fonti na Li s 24 3. Food and Feeding of Fish With Particular Reference to 25 the Benthic Fauna Pagq 3.1 Factors Affectjng Invertebrate Distribution 26 J.L Effect of Reduced Fl ows 26 3.3 Rakaia Invertebrate Studies 28 3.4 Food l-labits ôf F'ish 30 3.4.1 Native fi sh 30 Gal-axias macuTatus 30 Rhonbosol-ea retiaria 31 Retropinna retropinna 31 StokeLLia anisodon 31 Gobionorphus coti di anus 31 Geotria ausÈra-7.is 32 AnguiTTa dieftenbachij âlld ¿. austraJ.js 32 Gafaxias vuTgatis 32 Cheimarrichthgs fosteri and Gobiomorphus hubbsi 32 Gobiomo r phu s brev i ceps 33 3.4.2 Introduced fi sh 33 Salna gairdnerii 33 SaLmo trutta 33 Oncorhgnchus tshawgt s cha 34 4. Util isation of the Resource 34 4.1 Recreational Fi shing 34 ( j ) Trout 35 (i'i ) Sal mon 35 (iii) l,lhitebait 36 ('iv) 0ther species 37 4.2 Commercial Fi shing 38 (j) Eels 38 (ji) Salmon 39 (iii) Kahawai 40 5. Di scu ss i on 40 6. Acknowl edgements 7. Literature Cited 1. Rakaia River system. Patterns of majn migrations of fish'inhabitìng 42 the Raka'ia River system. 1. F'ish species inhabiting the Rakaia River. 2. Age structure of quinnat salrnon returns to 15 Gl enarì ffe. Numbers of adul t salmon entering Glenariffe 77 Stream 1965-1981 4. Incidence (%) of scale nucleus types from the Rakaia River. 1. 1. I NTRODUCTION Proposals for two irrìgation schemes and hydro-electric power generation exist for the Rakaia River downstream of the gorge. Construction of the Lower Rakaia (Pendarves) Scheme is proposed to commence in late 1981 - early 1982, and Fisheries Research Div'ision (FRD) understands that a water right for between 25-35 cumecs (l^J.J. Lewthwaìte, pers. comm.) will be applied for th'is year (1979). However, at this stage (September 1979) the Ministry of l¡Jorks and Development are unable to state exactly how much water will be appì'ied for. The main consideration for the river inhabitants will be the effects of reduced flows due to water abstract'ion during the irrigation season (September 1 - Aprì1 30). The question we, as fìsheries b'io'logìsts, are beìng asked to answer is "how much water can be abstracted from the Rakaia River before the existìng fishery is affected?" This impl'ies that there is a minimum flow wh'ich will maintain all fish species and also tends to cons'ider only the introduced specìes which are fished for by anglers" It overlooks the periodic high flows necessary to move bed load and flush out sediments (Stalnaker undated). It also ignores the dynamic nature of fjsh populations and the long-term recovery requirements of stream biota after a severe drought (i.e. a l-in-10-year event)" The stress conditions associated with the 1-in-lO-year low flow should under no circumstances be permìtted to become the norm. Stalnaker (undated) noted that aquatic ecology is more a descriptive science with a relativeìy recent and meagre theoretical basis for system simulation and prediction. Any hope that the aquat'ic eco'logist will be able to quantify the gaìns and losses in terms of number of fish produced in relation to any f'low regime is unfounded. Information on the timing of stream flows and the distribution of 2. hydraulic characteristics (depth and velocity) jn a stream are not sufficient to descrjbe fjsh production. To quote Stalnaker (undated) "until the physical scientists have developed predictive tools capable of describing changes in substrate distribution and channel form at the microhabitat level, the predictable quant'ification of the stream flow - fish production relationshìp under changing condit'ions will not be possible". The Rakai a Ri veri s typical of Canterbury r j vers, bei ng characteri sed by a wìde, braìded, shingle bed. The braided nature of the river makes quantification of res'idual flows even more difficult. The distribution of water within the river bed under abstraction regimes also needs to be known and the nature of the changes in water distribution imposed by f'loods and freshes described. Until thjs is done, it ìs virtually impossible to describe the effects of the proposed abstraction of 25-35 cumecs of water on the fish populations of the Raka'ia River. In thi s prel im'inary report, the f ish inhab'itants of the Rakaia River are described and their life histories, as far as is known, briefly discussed. The benthic invertebrates and their importance as fish food organisms are described and finalìy the recreational and commercjal values of the fish resource briefly outljned. 2. FISH RESOURCE Table 1 lists the fish presently known to inhabit the Rakaia River system, with their scientific and common names. 2.T NATIVE FI SH Native fish resident'in the Rakaia River can be divided into migratory and non-m'igratory species. All the migratory species require passage at some stage of their life hìstory as well as habitat within the river itself. 3. TABLE 1. Fish species inhabiting the Rakaia River. (i ) ESTUARTNE SPECTES * Gal-axias macufatus I nanga Arripis trutta Kahawai Al-drichetta forsteri Yeì 1 ow-eyed mul I et * RhombosoLea retiaria Black flounder (ii) L0WER RrvER RESTDENTS * Retropinna retropinna Common smel t * StokeLfia anisodon Stokel I 's smel t * Gobiomorphus cotidianus Common buì 1y (iii) 0THERS (prsTRrBUTr0N frtAy BE RESTRTCTED) * Geotria austraLis Lamprey * AnguitJa d.ieffenbachii Longfinned eel * anguiTTa ausÈra-Zjs Shortfinned eel * Gafaxias brevipinnis Koaro GaLaxias vuJgaris Common river galax.ias Gal,axias paucispondglus Alpine galaxias GaLaxÍas prognathus Longjawed galaxias * Sal-mo gairdnerii Rainbow trout ** salmo trutta Brown trout * Sal-vel-inus fontinal-is Brook char ** oncorhgnchus tshawgtscha Quinnat salmon * cheimarrichthgs fosteri Torrentfi sh x Gobiomorphus hubbsi Bluegilled bully Gobiomorphus breviceps Upland bul'ly * Migratory species + Introduced species 4. 2.I.I l'ligratory Speci es Those fish w'ith a migratory stage in their life cycle are marked with an asterisk in Table 1. (i) Estuarine Species 0f the estuarine species listed in Table 1, kahawai and yellow-eyed mullet are primarily marine. Both are known to enter river estuarjes on the rising tide, often in shoals" However, spawning and rearing of juveniles js marine in both species, RhombosaLea retiaria The black flounder is the only spec'ies of flatfìsh which lives in estuarjes and enters freshwater. (The remaining ten species of flatfish known from New Zealand waters are entirely marine (Manikiam 1969)). The biology of the black flounder has not been studied, and nothing ìs known of its reproductìon. However, in most flounders the eggs are found free-floating in the surface waters of the sea and McDowall (19i8) suggested the black flounder does not enter freshwater untjl after metamorphosis of the juvenile to the bottom-dwelling form. s.p. Hawke (pers. comm.) has observed juveniles moving into the Rakaia Lagoon in 0ctober and November. Gal-axias macuLatus The inanga'is the best known of the species of Gataxias and its iuvenile is the most important species in the whitebait catch. The inanga is unusual amongst galaxiids in that the adults are found in shoals. The shoals occur mostly in open, genily flowing or still water, such as in the 'lagoon. The life history is quite well known (McDowall 196g). Gat_axias macuLatus matures during its first summer in freshwater, and the r-ipe adults migrate downstream to the river estuaries, usually in the autumn, aìthough breeding has been recorded from September until June. These migrations coìncide with the full and new moons, and thus w'ith the very high spring tides that occur on these phases of the moon. Spawn'ing takes 5.