IMAFRolar,uø- tì bror¡

cAPtþ

Fisher¡es aspects of the Taharoa lakesand Wainui Stream

Fisheries Environmental Report No.66

Fisheries Research DivisionN.Z. Ministry of Agriculture and Fisheries

rssN 0111-4794

Fisheries Envìronmental Report No. 66

F'isheri es aspects of the

Taharoa I akes and

tiai nui Stream

by

R.R. St,ricrlarrd

Fi sheri es Research Di vi sì on

NZ Mìnìstry of Agrlculture and Fisheries

Rotorua

September

1985

FISHERIES TNVIRONI'IENTAL RIPORTS

This report is one of a series of reports issued by F'isheries ResearchDi v'is'ion on i mportant i ssues rel ated to env'i ronmental mattens. Theyare issued under the folIowing criteria:

(1) They are informal and should not be c'ited without the author'spermìssion.

(2) They . arq for I imited cì rcul ati on, S0 that persons andorgan'i satì ons normaì 'ly receì vi ng Fi sheri es Research D'i v j si onpubl i cati ons shoul d not expect to recei ve cop'i es automati cal ly.

(3) Cop'ies will be issued in'itìalìy to organisat'ions to which thereport is directly reìevant.

(4) copì es w'i I I be i ssued to other appropri ate organi satj ons onrequest to F'isheries Research Divisìon, Ministny of Agricultureand Fisheries, P.0. Box 9324, Riccarton, Christchurch.

(5) These reports will be 'issued where a substantjal report jsrequired with a tìme constraint, ê.9., a submission for a tribunalheari ng.

( 6 ) They wi ì I al so be i ssued as 'i ntenì m reports of on-goi ngenvi ronmental studi es for wh'i ch year by year or i ntermittenineportì ng i s advantageous. These i ntenj m reports wi I I notpreclude formal scientific publ jcation.

CONTENTS

Summany

Pa ge

5

5

7

1.

2.

I nt nodu ct'i on

Descri pti on

2.r2.22.3

2.4

?.5

Lakes Taharoa, Numìt'i , and RotoroaThe !,la'inu'i StreamNew Zeaìand Steel M'ining Limited's Constructionand Operat'ion of Fi sh PassMaori Fisheries at Taharoa2.4.L Bef ore Ironsand M'inì ng2.4.? Since Inonsand MiningThe t/a'inui Str^eam F'ish Pass

17

I2

3. Fi sh Speci es

3.1 Grey Mullet3.2' Grey Mul l et Popul ati on 'in3.3 Spawni ng of Grey Mu1 1 et3.4 Env'ironmenta'l Cond'iti ons

the Taharoa Lakes

for Grey Mullet

I4L41515

i8

2I2?2323

25

2626

27303232

4. Hi stori cal Revi ew of F'i sheri es Investi gatì ons and Reports

4.1+.24.34.44.5+.6

4.74.84.9

Di scuss'ion

Recommendat,i on

Acknowl edgments ,

Literature Cited

Ministry of Agriculture and Fisherìes (1977)Bioresearches Limìted (1977)Fìsneries Research D'iv'is'ion (L977)Auckl and Acc'limati sat,i on Soçi ety (i978)vJaikato Va11ey Authority (1979)New Zea.land Steel Mi n'ing L'im'ited and Fi sheni esReseanch Di vi si on ( 1981 )t,Jaikato Valley Authorìty (1983)Fi sher.ies Research Di vì si on (1983)Fi sheri es Research Di,¡ j si on (1984)

333639

39

43

44

44

c

6.

7.

8.

Appendi x

Appendi x

47I. F'i sh box t rap

Gill net samp'le sites, mesh sizes, andf I eet 'lengths

II. 48

1.

2.

TABLES

Page

Fìsh species necorded in l.la'inui Stream and Lake Taharoa 18Surveys and reports nelating to fisheries matt,ers at 19Taharoa

Comparison of grey mu'llet catches from Lakes Taharoa 30and l,laahi

4. Specìes reconded as ascending the Lake Tahanoa fish pass 38

3.

1.

2.

3.

4.

t:

6.

7.

8.

FIGURES

Location of places mentioned in text

Lake Taharoa

Lake Rot,oroa

New Zealand Steel Minìng Lìmited's m'ine s'it,e and l/ainuiSt ream

Fl oati ng i ntaKe of t,he f i sh pass

Downstream end of the fish pass

Stockpi I e drai nage outl et

Current veloc'it'ies in the Lake Tahanoa fjsh pass comparedw'ith swimming speeds of three native f ish

I9

9

10

11

16

?9

37

t-

5

SUMMARY

A grey mullet fishery at Lake Taharoa has been lost because accessfor juvenile mullet from the sea to the lake has been bìocked by a dam.Constructi on of the dam ai I owed New Zea'land Steel Mi ni ng L j mi ted (NZI4S)

to abstract water f or thei li ronsand mi ni ng operat'ion. A f i sh pass,whi ch was a cond'iti on of thei r water ri ght, was 'i nstal l ed to al l ow f i shaccess to the lake. Aìthough it js negotiable by some species, it'isìmpassable to mullet.

The various surveys conducted and reports produced on the fisheries

pnoblems at Taharoa are summarised and discussed 'in this report. Anumber of opti ons wh'ich wi I I assi st i n restori ng previ ous f .isheri esval ues are presented and acti on requ'i red by the part'ies i nvol ved toresolve the problem is recommended.

t. I NTRODUCT I ON

Lake Tahanoa and 'its interconnecting lakes, Numiti and Rotoroa, .arel'ittl e known to most New Zeal anders. To the smal I , i so'lated Maorisettlement of Taharoa these lakes pnovÍded ìrnportant food resources upuntil the 1970s. In 1968 a road was brought 'into Taharoa. Before th'isthe settlement's only commun'ication lìnk wìth the rest of the countrywas by boat to the north-east corner of the lake, where the road started

and a telephone was housed. In I97?, when land to the south-west ofLake Taharoa was leased to New Zea'land Steel Mining Limited for ironsandmining, Taharoa was finalìy linked w'ith the rest of the country by powerand telephone.

Mining created employment for the local peop'le, a viìlage was bui'lt,

and the community suddenly had most of the benefits of the modern world

6

pì aced at 'its doorstep . Thi s was , no doubt , an overwhe'lm'i ng seri es .ofevents and centain'ly a compìete contrast in pace of life for most of thecormunì ty . Under these c'i rcumstances the i mpontance of some of theintrinsic and cultural values of the conununity were understandablyoverlooked. Such values were the fisheries provided by the Taharoa

I akes and I,/ai nui Stream.

To mi ne, process r ôrìd transpont i ronsand at Taharoa, NZSM requ'i reslarge quantit'ies of water. The source of waten is Lake Taharoa. lr{aten'is drawn from a reservoir created by a dam on the lake's outlet - thel¡lai nui Stream. Dammi ng the l/ai nui Stream af f ected movement of al I f i shmi grati ng from the sea to Lake Taharoa. Foreseei ng some of theproblems that the dam would cause to the fishery, ìocaì Maoris madestrong demands'on the company to commission the desìgn and installationof a fish pass. A fish pass for mullet was made a condition of thecompany' s water ni ght, but, probl ems have ari sen w'ith the f unct'i on'i ng of

the pass. In particular, the grey mullet fishery has been affected tothe extent that by 1984 no grey mullet could be found jn eìthen LakeTaharoa or tila'i nui St ream.

Fi shen'ies Research D1vi s'ion (FRD) has been j nvol ved with thefish pass operatìon s'ince 1977 in an advisory capacity. Duning thistime several surveys have been conducted of Lake Taharoa, the l¡lai nuiStream, and the fish pass. F'isheries surveys and reports have been madeby other organi sati ons as wel I and it 'is the purpose of thi s report t,obring together recommendations concern'ing the Taharoa fishery.

This report also discusses possible opt'ions for overcoming thefreshwater fisheries issues associated with NZSM's operation at Taharoa.

F'inally, the report is intended as a means of briefing the variousgroups af f ected by and responsi b'le f or these 'i ssues, so that they may

dì scuss and deci de upon

mai ntenance of the t¡lai nui

7

an effective strategy fon the restonation and

Stream and Lake Taharoa fishenies.

2. DESCRIPTION

2.I Lakes Taharoa, Numiti, and Rotoroa

Lake Taharoa is about 4 km south-west of Kawh'ia Hanbour on the westcoast of the North Island of New Zealand (Figs.1 and 2). The lake hasan open water area of 224 ha wìth an extensive raupo-fìax-sedge wetland

fringe covering a funther 145 ha (Davenport 1983), Two smaller lakes,

Num'itì .and Rotoroa (Fig. 3), are ì nterconnected wìth Taharoa at 'its

southern end and lie in a south-west by north-east cha'in. All threeIakes are of the "dammed vaìley" type formed by an advancing foreduneblocking a stream valley (Hatton L977).

The maìn'inflows to the lakes are fnom a scrub and pasture catchment

on the'i r northern and eastern s'ides, and draì nage of the I akes i s by thel¡/ai nuì Stream to the Tasman Sea. Extensi ve beds of aquatì c macrophytes

occur t,hroughout the lakes; the bottom cover of the centre of LakeTaharoa j s mai n'ly characean meadow (c¡ara coraJJ.ina ), outs'ide of whi chare extens'i ve beds of Etodea canadensj,s, potomogeton cnspus , p.

ocl¡reaËus, P. cheesna¡ii and rgriophgllum Sp. (Davenport 1983).

2.2 The l¡lai nu'i Stream

Before it was modìfjed in L972, Lake Taharoa dra'ined free'ly into theTasman Sea vi a lilai nui Stream. The I,/aì nu'i was a I ow gradi ent streamwhich meandened along a 3 km course through sand dunes. Raupo fringed

much of the stream course and shalìow pools were formed at t,he meanders.

FIGURE 1. Locati on of pì aces ment i oned i n text.

FIGURE 2. Lake Tahanoa, looking from south to north.

FIGURT 3. Lake Rotonoa, looking from south to north.

Po

FIGURE 4. New Zealand Steel Mining Limited's rnine site and I'lainui Stream.

11

A 4.6-m-hìgh dam was bu'ilt by NZSM about 500 m from the sea and now

forms a reservoir which merges with Lake Taharoa. At the dam the stream

passes over a box weir and thnough two 1.5-m-diameter concnete p'ipes and

then across a concrete apron jnto the lower stream course. Ten metres

be1ow this the stneam passes over a 0.S-m-high wei r and continuesthrough the dune out to sea. Bef ore Decemben 1982, the þi ai nu'i Streamran parallel wit,h the sea fon about 200 m before it meandered out acrossthe beach to the sea. During a storm a portion of dune collapsed acrossthe stream where it formerly turned south to run paralìe1 w'ith thebeach. In an effort to unblock the stream NZSM shortened the course by

mechanically excavatjng a channel which now diverts the flow in almost adìrect line from the dam to the sea (FiS. a).

At the dam about 29 9"/sec of the overf low, negu'lated by a f'loatingintake (FiS. 5), is diverted through a fìsh pass wh'ich re-enters thelllainuj just below the 0.S-m-high weir. There is ljttle infornation on

.-1

,<

L2

stream flows, except that several times during the summer of 1983 theonly fIow in the t,lainuì below the dam was that which flowed from thefish-pass. J. Uerata (pers. cornm.) and Davenport (1983) also reportedthat in summen flows can be minimal, at times represented only by the?9 t/sec flowing through the fish pass. Therefore, minimum flows in the

I,lainui could be as low as 29 r./sec.

?..3 New Zealand Steel Mining Limited's Construct'ion and 0perationof Fi sh Pass

New Zealand Steel Min'ing Limited, a subsidiary company of NewZealand Steel L1mited, lease Maori land at Tahanoa for the purpose ofminìng ironsand. The mining operation has been in existence since 1972and has provi ded empì oyment, housì ng, and senvi ces for the Taharoacommunity. The company appears to pursue a high pubìic relationsprofile and in doing so works ciose'ly with commun'ity tnust,s and gr"oupsof Taharoa.

Two p'lants mi ne and concent,nate 'ironsand at Taharoa, and m'ini ng,processing, and transporting the ironsand relìes on the ava'ilabilìty of

a ìarge water supply

The ìarger of the two pìants operates in an excavated pond where afl oati ng dnedge and concentrat'i ng p1 ant mi nes and processes thei ronsand. l,later l eve'l i n the pond i s mai ntai ned by water pumped f romthe t.lainui stream, and by recycled slurry water. The concentrate isthen pumped as a sì urry to a stockpi 'l e area adj acent to the beach t,oawait shi pì oadi ng.

The second method of m'ining at raharoa is a dry feed plant whichonly requi nes water to pump the i ronsand (as a slurry) to a

13

concentrat'ing plant and then out to the stockp'iles. The volume of water

used'in both these minìng p'lants is about 4 600 r37duy, o. 11 000 13'ifthe water necycìing p'lant is not used (Mathews 1983), and this amount isallowed for by l,laikato Valìey Authority (l/{VA) waten right 4405.

The fjnaì stage of the operation is the shipìoadìng, where ironsand'is pumped 'in a sl urry through a 3-km p'ipel i ne to an of f shone buoy atwhich ships anchor. About 21 ships pen year are loaded. Loading takes

about 48 h and requi nes up to 135 000 m3 of water f on each shi p. l.lVAwater night 4404 allows the taking of water for shiploading punposes and

requ'ires that no water be taken for the purpose of mì n'ing duri ngshi p1 oadi ng.

Once the'ironsand has settled in the ship's ho'ld, accumulated slurry

watelis di scharged i nto the Tasman Sea at a nate of up t,o 67 500,3/¿uy, alìowed by WVA water right 440?,

Th'i s vol ume of wateli s provi ded by the reservoi r created by NZSMdammi ng the Wai nui Stream. lllvA waten nì ght 4403 al I ows thi s damprovi ded:

i. The crest height of the dam shall not exceed RL 11.58 m a.s.l.

shal I be des i gned, operated , andthe authonity.

3. A minimum flow of 29 9,/s shall be passed through the fish ladden atal I times.

4. The existìng steel pipe section of the fish ladder shall be modifiedto the satisfaction of the Authority by 30 June 1983.

2. A f i sh I adder^ around the dam

maintained to the'satìsfaction of

l4

In the earìy stages of operation, the resenvoir leveì was 8.71 ma.s.'l and between each boat loading the gate on the dam was opened to

drop the stream back to its natural level. This practice was apparentìyto alìow some control of aquatic plant growth in the resenvoin and toallow passage of rnignatony fish up and down the stream"

By 1975, NZSM's operation had'increased to the extent that it becamenecessary t,o ma'intai n a permanent water reservoi r on the Ì,,lai nui . Atsome stage during this perìod (date unavai1able) a fisn pass wasdesigned for and installed by NZSM w'ith the intention of maintainingaccess to Lake Taharoa for whitebajt and mullet. A consulting firm,Murray North and Partners, is understood to have engaged some AucklandUn'iversity engineering students to design the fish pass.

?,4 Maoni Fisheries at Taharoa

2.4.I Bef ore Ironsand M'i ni ng

The Taharoa I akes, the l,lai nu j Stream, and the surround'ing I and anesteeped in Maori hìstory and trad'ition. This is the land of the NgatiMahuta, descendants of t,hose who arrived in the Tajnu'i canoe and whomade first Iandfalì at Tahanoa before finally reach'ing Kawhia Harbour.

Before 1968 Taharoa was a tradit'ional Maori settlement, ìso1atedboth geographi ca'l ìy and soc'ial ìy f rom the rest of New Zeal and (Hi ggs1981). Under these circumstances the continued gathering took p'lace ofmany traditional food items, among which were fish provided by theTaharoa lakes and tdai nui Strearn. 0f primary ìmportance were mul let andeels wh'ich were valued because of their almost year round supply andwhich consequent'ly featured as food items at 'important functions on themalae.

15

Mullet were readily caught by net in the Taharoa lakes, and weresometìmes caught in large numbers in the tla'inu'i.Stream during summerwhen mature mul let mi grated out to sea. Duri ng these spawni ngm'igrations mullet were speared, gaffed, and even k'icked ashore from

shallow reaches of the stream. Eeìs were taken in h'inakis and sometimes

were speared oc gaffed. In spring, whitebaìt and smelt were caughtalong the tIa'inui Stream.

2.+.? Si nce Ironsand Mi ni ng

Curfentìy mulìet fish'ing no'longer t,akes pìace and many of the local

Maoris have expressed concern at the loss of this fishery. Fjsheniessunveys detai I ed 'in thi s report resulted f rom th'is concern.

Eei fishing still takes place and the continued tradit,ional use ofthis fishery has been safeguanded by the lake trustees, who do not allowany commercial eel fish'ing in the lake. A possible consequence of thisi s an abundant eel popul ati on i n Lake Tahanoa. l,¡hiteba'it'ing conti nuesonly ìn the ìower 100 m of the Wainuì Stream where fìsh congregate below

the dam and become vulnerab'le to capture. Before the dam wasconstructed, pressure on this fìshery was spread along the entire length

of the stream. Despite regul ati ons proh'ibìt,i ng f i shì ng near a f i shpass, dip netting takes place right up to and sometimes with'in the fishpass. l.Jhiteba'iting does not take place above the dam, which indicates

lhat whitebait do not reach this area, and locals compla'in that white-baiting was much better before construction of the dam.

2.5 The lllainui Stream F'ish Pass

Si nce ìts constructi on the fi sh pass has undergone vari ousmod'if ications, al I designed to improve 'its funct'ion. The downstream end

16

of the fish pass is located just below a 0.S-m-high weìr which wasconstructed across the blainui Stream to form a barrier to upstream fishmigrants in an attempt to guide them into the fish pass (Fig.6). Thewei r does not stop eel el vers and shri mps, and duri ng nesenvoi roverflows assoc'iate,J with h'igh stream flows, smelt, whiteba'it, ancibul l i es are known to pass oven the we'i n.

Ïhere are three stages to the fjsh pass. The first stage below thedam is constructed entireìy of wood, and 'it is reachìng a stage wheneeìther substanti al mai ntenance or repl acement 'is nequ'i red. Fi sh gaì nentry into a baffled box (of about t 13) and then are requìred to passthrough a 0.3-m-wide baffled flume to another box. These boxes wereintended as resting areas for fish migratìng up the pass and there are17 of them spaced at regular intervals and interconnected by baffledflumes. They extend to the lower side of the dam. At this po'int a0.6-m-diameter steel pÌpe aboul 25 n long passes thr.ough the dam to the

FIGURE 6. Downstream end of the fishthe tia'inui Stream desi gnedpassage upstream othen than

pass and the wei r onto pnevent fishby the fì sh pass.

17

neservoir. 0n the reservoir side of the dam the pipe is joined to the

wooden stage of the pass by a si mi 'l ar ' baf f I ed pass a͡d rest-boxstructure, except that, the flumes of th'is pass are enclosed, and it isconstructed of 6-mm ga'lvanised steel plate (see Fig. 5).

The opening or water int,ake to the fish pass is slung in af i bregì ass-encased polyurethane fI oat whi ch al I ows the compl etestructure to rise and fall according to reservoir levels so that apermanent flow is maintained in the pass. A galvan'ised trap was madewhìch fits over the fish pass where it opens to the neservo'ir so thatuse of the pass can be monitored (see Appendix I for design of trap).

The expansion of NZSM's operation at Taharoa ìn 1978 involvedra'i s'ing the water I evel ì n the resenvoi r by 1 m. Bef ore thi s ,Bioresearches L'imited were employed by NZSM to report on theenvi ronmental ìmpact on Lake Taharoa and the l/a'inui Stream of ra'is'ingthe reservo'ir' (sectìon 4.2).

Since 1978 the fish pass has been ìengthened by 5 m in an attempt to

reduce the water velocity t,hrough it, and gravel was fed down the steelp'ipe sect'ion and into some of the rest'ing boxes below the dam.

The onìy other mod'ification to the pass was a bypass which wasjnstal'led at the resting box at the lower side of the dam. This was to

a'llow a smali flow of water to ìntercept, eìvers whjch were cl'imbing the

side wall of the concrete apron below the dam and were becoming stranded

in the sand.

Finance and labour for all aspectsmaintenance, and 'improvements have been

the fish pass construction,respons'ibi ì ity of NZSM.

of

the

18

3. FISH SPECIES

Fish species from the Lake Taharoa system have only been recorded

since NZSM's presence at Taharoa.

The species listed in Tabìe I have been 'ident'ified 'in four FRDsurveys of Lake Taharoa and lilainui Stream (Table 2). From observationsof the numbens of juven'il e eel s mi grati ng up the l,/a'inui Stream, and of .adult eels in the lakes, eeìs are 1ikely to be the most abundant speciespresent. Howeven, there are several obstacles associated with NZSM'sopenat'ion whi ch I'imit juveni 1e eel movement 'i nto the ì ake (secti on 5) .

The surveys have not determined which of the two eel species'is the most

abundant, but ava'ilable hab'itat favours shortf ins and alì the eelscaught during a gill net survey were shortfins (Strickland l97B).

TABLE 1. Fi sh specì es recorded 'in y,la'inui Stream and Lake Taharoa

Common name Sc'ientìfic name

I

L

Fìounder spp

McDowall (1977) also lists giant kokopu (cal.axias argenËeus) as apossib'le inhabitant of t,he lake but this fish has so far not beenrecorded during any surYeys.

Anguil la die f f enbach! iAnguilla aust¡aLisRetropinna tetr^opinnaGa-laxias fasciatusGaLaxias macui.atusMugil ce.oàaJ.usGobionorphus hutËoniGobiomor phus cot idjanus

Patatga curyjrostrisP ar anephrop s planifrons

Crustacea

Fneshwater shrimpKoura

*tt

Recorded below NZSM dam.Recorded above NZSM dam (inc'ludes species caught in trap at top offi sh pass ) .Recorded 'in Lake Taharoa.

TABLE 2. Surveys and reports reìating to fisheries matters at Taharoa

Date Organi sati on Invol vement 0utcome/acti on

L977 MAF Memorandum to Minister regarding Not knownfi sh-pass

1971 Bioresearchers Environmental assessment of the Report to engineering consultantseffect of raising ìake level

1977 FRD Inspection of ìake and stream and Report with recorunendations to NZSMtaìk with NZSM and locals

1978 AAS Gill netted Lake Taharoa to assess No recruitment evident since 1974effectiveness of grey muììet and low numbers of grey mulletrecruitment via the fish pass present in ìake

Lglg HVA Inspection of waste discharge in Report to llVA for water rightI,lai nui Stream purposes

Remedial action by NZSM

1981-82 NZSM/FRD Trapping of fish reaching the Internal report by NZSM recommendingreservoir via the fish pass another giìl-net survey

1983' l.lVA Report i n connecti on with the Recommendati ons made concerni ngrenewal of NZSM water rights fish pass and need for water budget

1983 FRD Evaluation of fish pass design in Recommendations to NZSM made, but norespect of velocities and depth action received

1984 FRD Repeat sampìing of ìake to assess No muìlet caught or seenstatus of mulìet popuìation

rc)

20

At the end of their life cycìe eels migrate from fresh water to seato spawn. Young ee'ls enter fresh water in spring at about the 5ame time

as whitebait run. During their journey up freshwater streams eels areabìe to negotiate steep grad'ients and watenfalls prov'ided there are dampsurfaces availa[rle to wh'ich the eels can adhene. This can be witnessed

at the box weir on the t/ainu'i Stream dam.

Inanga and smelt are common ìn t,he l,lainui Stream and though they are

seen occasionally 'in t,he lake their abundance there is uncentain. Sincemodifications to the fish pass, and the construction of a we'ir at itsentrance, both these species appear to move through the fish pass ingreater numbens than previously (J. Uerata 1983). Both species requireaccess to the sea to complete their life cyc1e, and the return fnom thesea by juveniles of these spec'ies, panticuìanìy inanga, forms the bulkof the wh'itebait catch 'in the l^/aìnui Stream.

Another of the wh'iteba'it speci es, banded kokopri, whi ch were caught asjuvenì 1es durì ng the 1982 trappi ng i n the l^lai nuì Stream, ffiêV aì so formpart of the whitebajt catch on occasions, However, th'is was the onìymi grati on of thi s specì es that has been recorded 'in the l,lai nui Stream,and adults of the specì es have not been reponted on recorded j n thestream or elsewhere in the Taharoa system.

Common bul l'i es have been observed throughout the system andjuveni 1 es and adults of thi s speci es have been neconded 'i n thefi sh pass. Red-fi nned buì ìy juveni'l es have been caught i n thefish pass, but have never been observed elsewhere'in the system. Boththese bul ly speci es requi re access to the sea to compl ete the'ir l'if ecy.cì es .

2L

All of the species so far mentioned are affected by the NZSM dam,regardìess of the fact that each of them has been recorded in thefish pass. As well as these species there may have been othen moreecologically sensitive species present 'in the system before changes to

the stream and lake took place. One such species is.the giant kokopu

which, elsewhere in New Zealand, utiìises habitat typ'ical of Taharoa'sraupo-wetland margin.

3.1 GreY Muì ì et (Musil cePhalus )

The fall of the grey mu'llet fishery and the results of surveysi ndi c,ate that grey mul I et has been the most severe'ly af f ected f i shspec'ies in the system. Therefore the remainder of the repont w'i'l'l focus

on this species and the problems caused for it by mining deve'lopment.

Grey multet juueniles have been observed in abundance below the damìn the tllainui Stream during April to June of all years before 1983.

'\i nce 1983 no juven'il e mul I et have been observed i n the l¡/ai nuì Stream.

Thei r absence has been attri buted pantìy to the l./ai nui 's change ofcourse (in the dune area before'it enters the sea (see Fig.4)) whìchhas reduced'its length and created a shallower and faster run. Beforethis, shoals of grey mullet juvenìles used the warm, shaì10w, ponded orbackwater a'neas in these lower reaches. Th'is may have been important

\.. f or f reshly run juveni 1e grey mu'l I et m'i grants accl'imati si ng f rom sal'i ne

to freshwater conditions because there was aìways a noticeable increasein fish size in the shoals 'in an upstream d'irection.

0n a single occasion'in April L982 four juvenile grey mullet werecaught in the fish pass, but otherwise none have been seen entering thelake via the fish pass,

22

During a survey in 1978 grey mullet adults were netted in LakeTaharoa, but numbers appeaned to be very low. A repeat survey in 1984,with nets being used for twice the time that they were ìn 1978, fa'iIedto catch any mullet. hlithout surveys before NZSM's openation at Taharoait is d'iffìeult to essess the former sìze of the adult mullet populatìon'in the lake or how productive the fishery r.tas. However, localinformation'indicates that both were substantia'l and that fish could benetted at any time of the year j n the 1 ake; duni ng the sprì ngout-m'i grat'i ng grey mul I et coul d be ki cked ashore and sevenal sacksfilled at a time from the lower l,lainuì (P. Maikuku pers. comm.).

3.2 Grey Muì .let Popul at'ion i n the Tahanoa Lakes

The only publ i shed estimates of the s'ize of a mul I et popul at'ionre'late to the small 42 square m'ile* Lake Macquarie in New South þlales.About, 17 squai'e m'iles of suitable feedi ng ground supported 2 693 000mullet aged 1+ (I 777 400 lbt) when numbens were estimated with thePetersen method, or 2 540 000 (l 676 400 lb) when estimated by theSchnabel met,hod (Thomson 1966).

An average of these estimat,es g'ives 153 91i (10i 582 lb) mullet persquane m'iIe. In comparison, Lake Taharoa is much smalIer than LakeMacquanie; it covers only 0.9 square miles (excluding Lakes Numit,'i andRotoroa). To obta'in an estimate of the number of mullet the Taharoalakes could support, a feeding ground area proportional in size to thatof Lake Macquarie has been assumed to be 0.5 square miles. Based ontiri s, and assumi ng al I env'ironmental condit'ions for Lakes Macquarì e andTaharoa were s'imilar, about 76 955 (50 191 tb) grey mullet could beexpected to be present in Lake Taharoa.

square mile 'is about 259 ha.ìb is about 0.45 kg.

*1r1

23

3.3 Spawn'i ng of Gney Mul I et

tor augil ceplralus the breedìng season 'in some years can apparentìy

last for as long as 7 months, between March and September. The prec'ise

spawni ng t'Írne on both western and eastern coasts of Austral i a varieswith ìatitude; spawnìng occurs later in the northenn regions (Chubb,Potten, Grant , Lenanton, and l¡lal 'l ace 1981) . Inf ormati on on the ti mi ngof spawni ng was based on I arvae attaì n'ing a ì ength of 18 mm after. 42days under laboratory conditions, and on the fi nst appearance ofjuveniles 22-30 mm long in the Swan-Avon estuary of I'lestern Australiaduring May of 2 consecutive years.

In a sample of grey mul let juvenì les netted f rom below the Vlai nu'idam at the beginning of May 198i fish averaged 30 mm in ìength.Thenefore, the findings of Chubb et aI. (1981) appear to correspond withthe situation at, Taharoa, where the first grey nrullet juveniles appearedin about Apnì I and shoals were stlll not'iceable in Juìy. Furthermone,Wel I s (1976 ) concl uded that grey muì 1et f rom Lake r¡/aahi and the lJa'i katoRiven most likely went to sea to spawn from March unt'iì Juìy.

In Manch 1984 observations at the outlet stream to Lake Pokoroa,some 115 km (1 degree of latitude) further north along the coast fromTaharoa, showed large numbens of juvenììe grey mulìet about 30 mm longmigrating upstream and congregatìng in pools of the lowen reaches.

3.4 'Env'i nonmental Condì t'ions f or Grey Mul I et

Grey mullet ane found rough'ly between 42"N and 42oS jn all seas,though not as abundantly in the tropics as in the subtr^opìcs (Thomson1966). The world distribution of aagil'cephalus ìnd'icates that'it doesnot inhab'it waters whene w'inter temperatures dnop below 16oC or where

summer temperatures f a'i I to reach 18oC (Tfromson 1966) .

?4

In the þlainu'i Stream at Taharoa, temperatures have r^anged f rom 16oCto 23oC in summer and from 7oC to 16"C in winter. Howeven, large shoalsof juvenile mullet entered the Wainui Stream ìn Apriì LIBZ, whentemperatures of lToC were recorded, and small shoals were still presentin Juìy of the same yean, when the stream temperature dropped to 9oC.

t,lells (1976) suggested that mullet were attracted up the WaikatoRiver by eutrophic conditions wh'ich offered suitable food sources and

that grey mu11et pìayed a significant role jn maintaìnjng water qualìtyby directly uti'lìsing the nutrients and energy contajned in a'ìgae andmacrophyte detnitus.

Vi sua'l observat'ions of Lakerecent years water clarìty hasgreen 'in summer months. Thi suti I ì sed to the extent they were

Taharoa over 7 years confìrm that indeteri orated and 'is becomi ng not'iceab'ly

may ì ndì cate that al gae are not be'ingwhen more grey mul'let were present.

In Australia and the United States,spawni ng run have a di sti nct mi gratì on

coasta.l currents, but where currents are

very sl i ght (Thomson 1966 ) .

mature augil cephalus on thej r

pattern agaì nst the preva'i1i ng

sì'ight, coast-wi se movement ì s

Along the west coast of Nelv Zealand in the vicìnity of Taharoa, twocoastal curnents are known; t,he Westland curnent, whìch on occasìons

extends northwards from Cape Egmont to Cape Rei nga, and the westAuckland Cunrent which flows in the opposite direction, but which is nota permanent feature. These currents result i n hi ghly varì abl ec'i ncul at'ion aì ong thi s stretch of coastl i ne (Torteì I 1981). It i slìkely that in years when grey mullet juveniles do not enter the hlainu'iStream the cause could be due to a lack of stnong coastal currents,which bring the young back to parent waters. Thus, under natural

?5

conditions, irì some years there is probably a lack of certa'in greymuìlet year classes or fluctuat'ions 'in the strengths of year classes in

Lake Taharoa. This would create a drop in recru'itment following thebreeding years when weak year-cìasses reached maturity. This, and other

natural phenomena such as low flows, sand-bars closing access to thelake, and unattractive water quality and temperature, probabìy make

recru'itment in any year h'igh'ly variable. In addition, artificia'lbarri ers such as a dam, an i ncreased stream gradi ent, and a h'i ghvelocìty fish pass further l'imit, if not prevent, successful recruitmentof grey mullet into Lake Taharoa.

The presence of a'large eel population no doubt has had some effect

on grey mullet recruitment to the lake. Thomson (1966) reported that insome countries mullet are farmed as a forage fish on which to fattenfanmed eeìs; this ind'icates that gney mullet ane defìnite.ly acceptable'in the dì et of ee'ls. Because at least two-th'irds of the tlaì nu'i Streamhas been fonmed into a neservoir, wh'ich as a sìuggìsh and deep body of

water ìends rvell to eel habìtat, âñy juven'ile grey mullet whìch are able

to enter the resenvoir would probably have to survive predation by eelsbefone they found any shallow water habitat in the lake. This çastssome doubt on the effectiveness of the fish pass in recruitment of fish,because 'i n i ts present f orm 'it di rects mi grati ng f i sh st rai ght i nto t,hedepths of the nesenvoir. Coincident,ally, the same spot has a neputation

for bejng a good place to gaff large eels.

4. HISTORICAL REVIEI.¡ OF FISHERITS INVESTIGATIONS AND REPORTS

Since 1977, five fisheries surveys have been conducted and sevenreports compi ì ed on the f i sheri es i ssues assoc'i ated with Lake Taharoa

and the lllai nui Stream (see Tabl e ?) , Data and reports have been made

26

avaiIab'le to NZSM" However, during the past I years there have beennumerous changes of management personnel at NZSI'î. Consequentìy, many ofthe f i sheri es probl ems and reasons f or them may not have been fu]1yappreciated by success'ive personneì. The purpose of thjs section is tosummarise the various fisheries investigations and reports available, toalìow a better understand'ing of the probìems which still exist in thefisheries at Taharoa so that a fresh appnoach to soìving the problenscan be made.

F'isheri es i nvest'i gati ons at Lakebefore L977 are unknown. Objectives

designer's brief are also unknown.

ïaharoa or of the t¡lai nui Streamof the fish pass design and the

4.1 Ministry of Agriculture and Fisheries (197j)

The earl'iest record of Ministry of Agniculture and Fisheries (MAF)involvement is deta'iled in a memorandum to the Minister of Agriculturefrom the D'irecton-General (MAF fiIe 42127/0 dated 2 November I977 ) andstates that, "At least one inspection has been made by Mr R.1il, Litt,le,Sen'ior Fisheries Management 0fficer (Freshwater) and Mr E.N. MacDonald,Reg'ional Fìsheries Officer, Auckland. Mr Little reported that thefish pass was badiy designed and had some serious shortcomings, in fact,that it was most unìikely to achieve its purpose,,.

This memorandum probab'ly resulted from an enquiry by the Ministerafter a vis'it by hìm to Taharoa that year, though this, and also whetherany action resuited irom the memorandum, .is unclear.

4.? Bioresearches Limited (1977)

A brief ìnspection of Lake Taharoa and env'irons was conducted inL977 by Bìoresearches Lìmited to assess the ecolog'ical condition of

?7

Lake Taharoa and the effect of further rais'ing lake levels (Hatton

L977). A report was produced for Murray-North Partners Limited, theengì neeri ng consultants for t,he NZSM extensi on, and 'it detai I ed vari ousfi sheri es i nformati on as fol I ows:

1. Five species of fish utilise Lake Taharoa and a traditional fisheryis based on the'in occurrence.

2. Regard'ing an increase of over 0.5 m in lake level, the effect on thetradìtional fishery in the lakes should be negligìble and impnoved

access to Lake Numiti and Lake Rotoroa would occur.

3. It is critical to the survival of the lake fish population that thefish pass be operated correctly, irrespect'ive of lake level changes.The timed release of water t'o simulate "freshes" must be continued

t,o retain a v'iable fishery 'in the lakes.

4. exi sts and 'is based l arge'ly on eeland line fishìng), mullet fishingseasonal whìtebait'ing (dip netting).

No releases of exotic fish species have been made into Lake Taharoa.

No commerci al f i shery ex'ists.

4.3 Fisheries Research Divis'ion (1977)

After a vis'it to the m'ine site at Taharoa in 1977, Dr R.M. McDowallreported that long- and short-finned eels, inanga, mullet, and perhapsgiant kokopu were present in the Taharoa lake system, and that, themovement of al'l these species v{as affected by the NZSI'I dam.

McDowall doubted whether the fish pass was working because waterveìocities were too high as a result of gradient and flow voìumes, but

A tradjt'ional natural fishery

fisning (spearing, nett'ing,(spearing and set netting) and

5.

6.

28

he considered that the float'ing'!ntake, about to þe constructed, couldsol ve some of the probl ems. He al so doubted whether sì gn'i f i cant numbers

of fish were successful'ly negotiating the steel pipe section whichpasses through the dam, and he suggested to NZSM that the bed of thepipe be covered to a depth of 10-15 cm w'ith smallish rocks and gravel to

allow fish to settle and rest on the bottom wh'iìe they moved upstream.

McDowal I sent thi s report to the m'i ni ng managen of NZSM atGlenbrook and suggested that the company consider having a study of fish

movements i n the stream and I ake conducted by consultants or auni versìty student.

Conclusions and recommendations from McDowall's report were asf ol 'lows :

1. Failune of mullet to reach thethe I ocal Maori popu'ì ati on who

is the habitat where the fishare caught.

lake does affect a food resource for

regard this as ìmportant. The iakegrow to matunity and where the fish

2. Studies should be made of inflow rates, outflow rates etc., and awater budget for the whole system should be prepared that allowsNZSM, w'ith proper safeguards, to pned'ict'its needs and to releasesurpl us water.

3. That the lower 30-50 m of the pass be modified by the pìacement ofrocks of 5-10 cm diameter ìn the bottom, and that the pass abovethis be trapped to assess t,he results.

4. That a wall be constructed lead'ing out from the mouth of the pass atsuch an angl e that a gyre f orms 'i n the pool so that f .ish areattracted 'into the pass.

5.

?9

That, as an alternative to the fish pass, the company could cons'ider

trapping migratory fish and manually transferring them over the dam

on a regular bas'is, which may seem a tedious job, but which'in the

long run may prove the simpìest solut'ion to the prob'lem.

6. Concern v{as also expnessed at the quality of the water (stockpiledra'inage) being released into the lower reaches of t,he þlajnu'i Stream

' (Fig.7) and it was suggested that the company cons'ider somealternat'ive method of water disposa'l such as settlement ponds orspray irrigation.

N0 'immedi ate act'ion took place as a result of these recommendatì ons,though 'in I ater years recommendat'ions 2, 3, 4, and 6 r.ecei ved someattention indirectly as a consequence of other adv'ice and water rìghtnequi rements.

FIGURE 7. Stockp'i I e dra'inage outl et di schargi ng i ntotlainui Stream before stream course change.

30

4.4 Auckl and Accl i mat'isati on Soci ety (1978)

In May 1978 the Auckland Acclimatisatìon Society (AAS) gill nettedLake Taharoa to establish the age of any grey mullet present, and todetermi ne the effect of the dam and the effecti veness of the fi sh pass

on recruitment of grey mul I et i nto Lake Taharoa (Stri ckl and 1978) .Before this sunvey a verbal agreement was given by the project manager,NZSM, Taharoa'in the presence of Messrs Howard, Strickland, Maikuku, and

Keepa to have the fish pass redesigned ìf the AAS could show that mulletwere unabìe to negotiate the exist'ing fish pass. A further meet'ing r,rasto be arranged between NZSM and the MS once the results of the surveywere known.

0ver a perìod of 22 houns 16 grey mullet were caught. These fishwere aged w'ith the method described by Vlells (1976), and a subsamp'le was

a'lso checked by l,lel'ls to verì fy the age estimates. After makì ngallowance for the growth period, Lhe youngest mulìet, caught were fishwhich would have entered Lake Tahanoa in 1973. The Taharoa catch wascompared with catch figunes neported by t¡i el ls (1976) f rom Lake t¡,laahi(Tabl e 3) .

TABLE 3. Comparison of grey mu'llet catches from Lakes Taharoa and tlaah'i

Taharoa(caught during a

Age

si ngl e

Number

h set)

mul ì et

22

of

l,laahi(caught over 12sets per month)Age

months with 2 x 24 h

Number of muìlet

5

359061

7

65

432

?6I

6+5+4+

.31

As with the bJaahi study,2- and 3-year-old mullet should have been

caught in Taharoa. The absence of fish from these year classesind'icates t,hat mu'lìet wene no longer able to neach Lake Taharoa despitethe installation of a fish pass. Adult mullet in Lake Taharoa weneprobabìy those wh'i ch had mi grated up the lllai nu'i Stream bef oreconstruction of the dam or at times when t,he gates on the dam wereopened between shiploading during the first years of mining. In betweentimes many mature fish wou'ld have migrated to sea or been caught, but nomullet,'incìuding juveniles, were able to neturn.

At the t'ime of the 1978 survey,

observed shoali ng bel ow the dam i n

f ound 'in the fi sh pass or above the

A further i nd'icati on of the I ack of mul I et recru'itment 'in LakeTaharoa resulted from a comparison of the catch nate per net for Tahanoaand Laker¡laahi for about the same time of year. In Taharoa 1.3 fish per.net were caught, whereas 'in Vlaahi 12 fi sh per net were caught.Theref ore 'it was concl uded that f ewer mul .let were present i n Taharoathan could have been expected, whìch, with the absence of the younger

age classes of mullet, indìcated a lack of recruitment. This wasconf i rmed by l ocal Maori s who prev'i ous'ly had witnessed shoal s of mul I etmov'ing about the I ake and occasi onaì ly jump'ing: because they had notseen such events for several years they assumed mullet were no longerentering the lake and had given up fishing for them. During the 1978sunvey caìm cond'itions prevai ìed and special efforts were made toobserve mul'let shoals, without success.

Follow-up of the survey objective was never carried out by the AAS.

juvenile mullet (0+) were caught and

the l,lai nui Stream, but none coul d be

dam.

4.5 l{aikato Valley

32

Authorìty (1979)

waste d'ischarge 'into the l,lainui Stream was carried

Dr P. Henriques, a biologist w'ith r/¡VA. In histhe b¡VA resources manager, Henniques noted the

An i nspection

out in Îtlay L979subsequent report

f ol 'low'i ng:

of

by

to

The l,lainui Stream apparent'ly at one time supported a local ìyi mportant wh'iteba'it f i shery and Lake Taharoa supported a 1 ocal lyimportant mullet fishery. Both these fisheries are at present muchneduced and this is probabìy due to one or both of the follow'ing:

I. A dam on the tlai nui Stream, and an i nef f i ci ent f ish 'ladder.

2. ïhe discharge 'into the stream of stormwater, pr.ocess water, andunder-stockpi I e draì nage water.

Certaj n mati,ers reponted by Henri ques re1 atì ng tc the wastedìschange were attended to by NZSM, but the rema'inden, and all otherNZSM d'ischarges at Tahanoa, are currently cont,ro.ll ed by ìr/VA waterr''ights.

4.6 New Zealand Stee'l Min'ing and Fisheries Research D'ivisìon (1981)

After a request from NZSM's mining managen in September 1980 for FRDto assess the fish pass, a sunvey was designed wh'ich involved NZSM staffmonitoring fish movement Ín the pass by trapping the water intake to thefish pass at regular intervals over 2L months. Results from thistrapping were necorded by Uerata (1983) and are summarised as follows:

A trap was designed (see Appendix I) wh'ich fitt,ed on to the end ofthe fish pass where water flows in from the reservoir. Operation of the

l-

33

trap started on 1 May 1981, with an overn'ight set of about LZ hours.For the first I months of trapping the average number of fish caught perset was 17 , whi ch i ncl uded smelt, i nanga, ee'ls, and bul l'ies, but whi chwas dominated by inanga. After installation (in March L982, see sect'ion

?.5) of the weir at the bottom end of the fish pass and of the fivemetre extensi on there was a 54% 'increase i n the tota'l number of f i shcaught in the trap. Smelt and inanga were the most abundant speciescaught and showed an i ncrease i n numbers caught, of 83% and 43%nespect'ively, with inanga stiìl dominating the catch. Banded kokopu, aspecies p'reviously unrecorded in the Tañaroa system, also were caught at

various times between September and Novemben 1983. The first greymulìet juveniles to be trapped after the modificat'ions had been madewere four juveni'les caught on a single occasion on the second trapping

after the modifications were compìeted (April 1982). This coincidedwith a period when large shoals of grey mullet juveniles could beobserved below the dam.

During the I98? trapp'ing season between 30 and 50 juvenile mulletwere tnansferred manually from below the dam into the lake. The reportconcluded that, apart from this release, some restockìng of grey mullethad taken place via the fish pass and that another netting programme toprove the effect'iveness of the fish pass was required.

4.7 ldai kato Val 1 ey Authori ty ( 1983)

In 1983, 'in response to various appf icat'ions by NZSt'l for renewal ofwater rights alìowing them to dam, take, and discharge water at, theTaharoa operation, a report was compiled by I.IVA bioìogist, M. Davenport

who made some of the following comments:

34

"The dam cneates a serious hindrance to fish m'igration although theex'i sti ng f,i sh I adder al'lows the mi grati on of numbers of some specì es .Reinstatement of fishery values to cond'it'ions approx'imatìng thoseex'isti ng bef ore i nstal I ati on of the dam woul d requ'ire removal of that,obstructì on.

"Mi gratory access for fì sh from the sea to the Taharoa I akes ì s'important because:

- Eels and mullet once provided a lake fìshery.

- The wh'itebait runs provi de an important seasonal f ì sher-y.

- Mullet feed d'irect'ly at the first trophìc level ie green plants,detrjtus and algae. They may play some role in the maintenance ofwater quality of shallow lakes.

- Fi sh l'if e forms an impontant food soL¡rce f oi bi rds and otlrer f i shfeeding at higher troph'ic levels.

"l^/'ith r^espect to the exì stì ng f ì sh I adder, several areas coul d beexplored to ìmpnove ìts effic'iency:

(i) The present pìpe sect'ion passing from the dam under the road tothe lowen sect'ion of fish ladder is unsatisfactory. Modificationon neplacement to perm'it lower veloc'it'ies and r^estìng facil'itiesf or mj gratory juven'i I e f i sh are nequ'i red.

(ii ) Information on max'imum swimming speeds and on nanges of veloc'itiespromoti ng shoa'l'ing for a number of specì es has recentìy becomeava'ilable. An examinat'ion of velocities within the fish ladderand modi f i cat'i ons, 'if necessary, shou'ld be carr.i ed out.

1.

35

('iiì) Aìthough a very small number of juvenile mullet have been recordedpass'ing to the I ake v'ia the I addelit i s most unl i kely that theladder is, or ever wil'l be, capabìe of providìng mìgratory passageto s'i gni f i cant numbers of these f i sh . Seri ous consi denati onshould thenefore be given to the manual transfer of juvenì'le fìshfrom the Wainui Stream to the lake whi.lst the dam'is'in existence.

"Recommendati ons :

should a right be granted to dam (exìst'ing) the wa'inu'i stream, it isrecommended that the present p'ipe section of the fish ladder bemodi f i ed or repl aced to create rest'ing stages for m'igratony fi sh andfIows appropriate to juveniIe fish migration.

Should a right be granted to take water from the resenvo'ir createdby a dam, it is recommended that a waten budget be prepared. Thisbudget shoul d t,ake 'into account i nf I ows to Lake Tahanoa and mì ni ngoperation demands and permìt the maximum natural flow over the dam

i nto the ì¡lai nuì Stream.

shoul d a ni ght be granted to di scharge stormwater and ì ronsandconcentrate stockp'i1e draìnage water to the Tasman Sea, jt jsrecommended that provi sì on for di vers'ion of some or al I of th'iswater to the dam on the l,,la'inui stream be cons'ider.ed. In the eventthat pnesent on future treatment procedures can produce a dischargeof a quality compat'i.ble w'ith fisheries requirernents, such provis'ionmay be of considerable benefit to the maintenance of a water budgetf or the f'Jai nui Stream. "

2.

3.

36

These recommendati ons were adopted by the Regi ona'l l,later Board'sstanding tribunal when they recommended'the granting of NZSM's waterrights (section 2,3) on 14 March 1983. At this time the tribunal alsoobserved that:

"2. The lake (Taharoa) is a wildl'ife area and gameland habitat of somenote and once supported a loca'lly significant freshwater fishery.

3. The ex'isting dam is important to the maintenance of the w'ildlife andgarnebi rd habitat i n the I ake and its surrounds. The dam i S,however, a barrien to migratory fishes, most notab'ly the mullet.The tri bunal notes that the app'l'i cant (NZSM) has operated afish pass ìn the past and has expnessed its commitment to cont'inuingand improving its openation."

4.8 FisherÍes Research Divis'ion (1983)

In May 1983, FRD examined the fish pass to determìne which aspectsof its design and openation were ìnhibitìng tlre movement of fish,particularly mullet. Curnent veloc'ities at the top and bottom of eachflume and in each resting box were measuned and compared with theswimmìng ability of three native fish specìes (Fig, g). In the neportof t,his work (strickland and M'itchell i983) tne swimming speeds andbehavìounal adaptations of fish species reported as having ascended thefish pass were also presented (Table 4). Figure I cìearly showed thatgrey mullet would have found it difficult, if not imposs.ible, topenetrate beyond the third flume. It was also cons'idered t,hat depths inthe fish pass, wh'ich ranged from 3-10 cm in the flumes and 15-20 cm int,he rest-boxes, were too shaììow to attract fish into and through thefish pass. Finaìly, the report reconunended that because the wooden

1-4

1.3

1.2

1.1

1-

o.9

o.8

o.7

o-6

o-5

o.4

Velocity range in resting boxes

Maximum speed (2-5 mins)

Burst speed (less than 3O secs)

-{.

ooU'

E

.=ooo

(,!

o.3

o.2

o.1

o

lvers

Mullet

12Stream

9 10 11 12Flume number

20 21LakePipe

Above ilam

three native fisn"

lnanga

FIGURE 8. Current velocit'ies in the Lake Taharoa f isn-pass cornpared wìth swimming speeds of

38

fish pass was deteriorating and wouldbasìc design should be re-examined and

prov'i de a constant depth of at ì eastgreater than 0.15 m/sec thnoughout, that

soon have to be repìaced, theif it could not be modified to30 cm and a water veì oc'ity no

a nevt design be implemented.

TABLE 4. Species recorded as ascending the Lake Taharoa fish pass

Speci es Maximum speed(sustainable for atleast 2-5 minutes)

Burst speed(sustainab'le fon lessthan 30 seconds)

I nanga(Calaxias rnacutaËus )

Smelt(Retropinna retropinna )

Banded kokopu(calaxias fasciatus)- speeds for whitebait

j uveni I es

Short-fi nned eel el ver(anguiTta ausùraLis ) adult

0.38 m/s

0.23 m/s

0.34 m/s(then moves out ofcurrent and exp'lo'itsboundany layer)

0.37 m/s0.31 m/s

1.25 m/s

0.93 m/s

Can cl i mb out ofwater to pass hi ghvelocity areas

0.7 4 nis1.26 nls( can aì so cl i mb outof water to passhigh ve'loc'ity aneas)

Not known

1.03 m/s

Not known

Can puìl itselfthrough high velocityareas by cì'ingi ng tobottom

Long-fi nned eel(anguilla die f fenbachii )

Common bul iy(Cobionor phus cotídlanus )

Red-fi nned buì 1y(coøionorphus hutt oni í )

Freshwater shnimp(e arat ga curvirostris )

Not known

0.28 m/s

Not known

0.38 m/s(moves out of currentand clings to bottom)

Speci es unabl e to

Grey mullet(uugil cepiralus )

ascend the fi sh pass

0.19 m/s 0.28 m/s

39

Although this report elicited no response from NZSM' a foìlow-up

letter eventua'lly resulted in a repeat survey of the gill-netting'in'itÍally conducted by the AAS (section 4.4).

4.9 Fisheries Research Div'ison (1984)

In November 1984, FRD repeated the 1978 giì1 netting survey toestablish whether there had been any change in grey mullet numbers inLake Taharoa since 1978. Replicate fleets of gì1ì nets were set at the

same iocations as in 1978 (Appendix II) for a period of 40 h.

Netting was carried out Ín November to maximise the chances ofcatch'ing mul I et because b{el I s (tgZ6) had reported that mul I et catches i n

Lake blaahi were highest in Novemben and mullet were most frequentlyobserved between November and February.

However, no mullet were caught or seen during the survey. The lack

of f i sh i nd'icated that the popul ati on of mul I et whi ch remai ned 'in theI ake after the dam on the r,,lai nui Stream was bui ìt had either d'ied out orthe population was so low that it could not support a fisheny.

5. DISCUSSiON

Superfi c'i al ìy, fi sheri es probl ems at Taharoa woul d appearnegl i gi bì e; a dam across the þ,lai nui was compensated f or by a f i sh pass

and fish were known to use it.

Unfontunately there wene no fi sheri es surveys of Lake Taharoaconducted before the initiation of NZSM operations so it is d'ifficult todetermine the full effect of the development on the fish and fisherieswhich ex'isted. However, local Maoris report that sizeabìe catches of

mullet, eels, and whitebait occurred before the dam was constnucted.

40

It has been shown that mulletdevelopment to the extent that therethe lake or stream.

have been affected by the NZSMis no ìonger a mul'let fisheny in

According to comments by locals, the eel fishery appears to haveremained unaffected, though any effect which the dam may have had, or

may be having, on eel stocks could take many years to show up becauseeels are a long lived species; they live up to 30 years or more andmigrate out of the system only at the end of their life cycìe.

The whitebait fishery has been reduced from a stream wh'ich provided

3 km of fishable water to one wh'ich provides barely 200 m, therebycausing some rivalry among those who want to fìsh there.

Pressure from locals on NZSM to ensure the cont'inuation of formerfisheries has never been very strong, due partly to the fact that jobs

created by the mi ni ng operatì on changed l"he ìocal s ' sut¡sì stencelife-style, which included fìshing. However, sufficìent tìme has nowpassed for loca'l Maoris to have experienced the loss of former fisheriesand f or them to des'i r"e the restoratì on of those val ues. To achi eve thi sand also maintain employment through cont'inuation of NZSM's ironsandoperation might appear mutua'lly exclusive. However, with some careful

thought and perhaps some concessi on, there 'i s room for mi nì ng andnestoration of the fisheries. t¡ith this objective, the foltow'ingopt'ions are presented for the consideration of the parties ìnvolved:

1. The pnesent fish pass is obviously not achieving its purpose and anetr pass designed to achieve veiocit'ies of less than 0.15 rnlsec andmaintain a water depth greater than 30 cm in the pass should beinstalled. This would involve replac'ing the present pipe sectìonunder the road and continuing the new design throughout the ent'ire

length of the fish pass.

z.

41

Enhancement of grey mul 1 et juven'i I e habi tat bel ow the dam i snecessary and could be simply ach'ieved by rea'lign'ing the stneam back

to its original course, thereby reducing water veloc'ities andcreating shallow ponded rest areas.

Enhancement of juvenile eel recruit,ment would be achieved by making

several cuts in the crest of the box-weir to allow a trickle ofwater down the concrete faces. Young eels wouid then be able toclimb the weir and reach the reservoir more easily.

Maintenance of a defìnite lip to the stockpile dra'inage outlet pipe,as it was before 1983 (see F'i9.7), would ensure that juveni'le eelscont'inue up the l,,lainui Stream instead of be'ing diverted and becomìng

st randed 'i n or bel ow the stockp'i I es . Real i gni ng the st neam back t,oit,s oìd course would ass'ist in mainta'ining the lip.

Items 2,3, and 4 above are essential regandless of the fish passdesi gn and j f mul1et are to be encouraged to enter the I,iai nu'i Stream;'item 2 is of particular ìmportance.

Should a suitable fish pass design not be found or be prohibitively

expensi ve, several other alternati ves have been I'i sted to promotedi scussi on about the most effecti ve ways of re-establ i shi ng formerfi sheni es val ues.

1. Remove the dam and nepìace it with a bridge so that the t,la'inu'iStream can revert to its or''i gi na1 f orm or, 'if thi s does not occurnaturally, remodel the stream accord'ingly. Install the NZSM water'intake in Lake Taharoa. This would allow fish passage in the l,/ainui

Stream at alì times other than when NZSM water requ'irements areproportionaìly higher than the natural lake outflow. Reapplication

3.

4.

z.

42

for water rights would be necessary and as a cond'ition these should

incorporate a carefulìy prepared water allocation plan to ensurethat continuous low flows are safeguarded during t,imes of fishmi grat'ion. ,

De-water the reservoir and allow the l,lainui Stream to return to itsprev'ious gradient and character between boat loadings, especialìy

from April to Juìy when juvenile grey mullet migrate'into freshwater

from the sea. There is evidence indicat'ing that such a practìceallowed recruitment of juvenile mullet during the early years ofNZSM operation at Taharoa. Some remodeìling of the stneam coursewould be necessary to ensure that it was s'imilar to its formercharacter. De-watering rates would need to be slow enough to avoidfish strand'ing and bank scouring.

Install a iock system whereby fish slvim upstrearn to a dam and thenhave a sluice gate dropped beh'ind them and the top dam opened up to

allow the fish to enter the lake. The downstream sluice could beincorporated into the exìsting dam and the upstream sluice wouldneed to be I ocated as f ar upst ream as poss ì b'l e, to t rap ì ar.genumbers of fish in the lock. Ther^e would need to be a nes'idual flowma'inta'ined in the þlainu'i be'low the lowen dam to avoid fish strandìng

ì n that secti on whi 1e the 'lock was be'i ng f i I I ed. De-wateri ng andrefilìing rates would need to be slow enough to avoid fish strand'ingor bank scouring; they would probably require a 24 h period eachwây, depending on stream flow. As in 2 above, some remodelìing ofthe stream course would also be requìred.

4. Since juvenile grey mullet are the only fish unable to negotiate thefish pass it may be necessary to catch and manualìy transfer these

3.

43

fish into the reservoir or lake as well as to maìntain a proper-'lyfuncti oni ng fi sh pass for other speci es . Thi s woul d ì nvol veemploy'ing a person during autumn to trap juven'ile mullet and totransfer them into the lake. If an efficient trapping faciì'ity wasconstructed, this operation would onìy take about 15 minutes per dayor as runs dictated.

Apart from the various options discussed so far, if juvenile greymullet cannot be encouraged to enter the wainu'i stream it may benecessary to re-establ'i sh an adult popul ati on 'i n the I ake with mul I etfrom Kawhia Harbour on elsewhere. If juveniles have a tendency toreturn to parent waters or re'ly on cues provided by mature mulletalready nesiding in the lake to migrate up the stream, the absence ofmullet ìn the lake could be inh'ibit,ing juven'ile migration.

The peak time for juven'il e mul I et mi grati on 'into f reshwater betweenTaharoa and Manukau appears to be from March to May. A'lthough this js

earlier than mìgratìon t'imes reported in Australia, the latitude is sixdegnees further south than the Austral i an I ocati ons (Swan-Avon Ri venmout,h 32o04's) reported by chubb et ar. (1981). unfortunateìy Manch andsometimes April are months when some of the lowest f'lows have beenrecorded'in the tla'inuì Stream. Therefore alIocation of sufficient waterflows at this tìme of t,he year is crucial for juven'i1e grey mullet move-ment'into the t¡lainui Stream.

6. RECOMMENDATION

New Zealand Steel Mining

have made a commitment, to(sect'ion 4.7). t/e therefore

Lìmited have expressed a desi ne, and i ndeed

improve the fish pass operation at Taharoa.recommend that NZSM call a meet'ing with the

44

Taharoa Lake trustees, trlaikato Vaìley Authority, Fisheries Research

Division, and the Auckland Acclìmatisation Society to cons'îder whatactions would best remedy the fisheries problems discussed in thisreport.

7. ACKN0bJLEDGEMENTS

This report owes much to the interest and efforts of Patrick Ma1kukuand,.John Uenata of Taharoa. Patrick has been relentless in seeing thatthe fisheries problems at Taharoa are solved, and John monitored thefish pass for 2 years and put much t,hought into its 'improvement.

Many thanks to the hospital'ity of NZSI'! when vi s'its to the I akeinvolved overnight stays.

Charles Mitchell's help and suggestions with two of the surveys, and

hi s data on f i sh swi mmi ng speeds are great'ly app reci ated, as 'i sFrank Thompson's help with some of the eanlìer work.

Laurel Teirney's comments and advjce on the draft manuscript helped

this report take its fina'l shape.

8. LITERATURE CITED

Chubb, C.F., Potter, I.C., Grant,tllallace, J. 1981. Age structure,mul I et , l|ugil cephalus l-, and

forsteri (Valencíemes ), i n the

AuStfalia. Aust¡al.jan Journal ot

32 z 605-628.

C.J., Lenanton, R.C.J., andgrowth rates and movements of sea

,vel l ow-e_ve mu'l I et, aldrichettaSwan-Avon Rjver system, Western

Matine and Freshwater Resea¡ch,

45

Davenport, M.W. 1983. [,later night applications, New Zealand SteelMining Limited, Lake Taharoa and t¡lainui Stream. Unpublishedmanuscri pt . I,/ai kato Vaì ì ey Authori ty.

Hatton, C. L977. An assessment of the present ecoìogica'l condition ofLake Taharoa and the effect of further raising lake 'levels. Report

to Murray-North Partners L'imited. Bioresearches Limited, Auckland.

Henriques, P.R. Ig7g. New Zealand Steel Mining Ljmited, discharge into

the þlai nui Stream. l,lai kato Val l ey Authority i nternal repont PRH/15.

Higgs, G. 1981. Taharoa, surveypapet IVo Jl , Centre for MaoriI.lai kato.

of a changing community. occasíonal

StudÍes and Research, University of

Mathews, R.J . 1983. Appl i cati ons by New Zeal and Steel M'i n'i ng Li mi tedfor water rì ghts i n respect of i nonsand mi ni ng operatì ons atTaharoa . Unpubi i shed manuscri pt . I,la'i kato Va1 'ley Authority .

McDowal I , R.M. 1977 . l,lai nui Stream-Lake Taharoa. Unpubl ì shedmanuscript. Fisheries Reseanch Divìsion, Ministry of Agricultureand Fi sheri es, Chri stchurch.

Strickland, R. 1978. Grey mullet survey - Lake Taharoa. Unpub'lishedmanuscript. Auckland Accljmatisation Society.

Strickland, R., and Mitchell C. 1983. Report on the design efficiencyof the Lake Taharoa fish-pass. Unpublished manuscript. FisheriesResearch Divis'ion, Ministry of Agriculture and Fisheries, Rotorua.

Thomson, J.M.

B'iol ogy " .

p 301-335.

1966. The grey mullets. "0ceanography and MarineGeorge Al'len and Unwin Limited, London. Vol 4,

46

Tortelì, P. (Ed.) 1981. "New Zealand Ailas of coastal Resources',.Government Printing Office, Wellìngton.

uerata, J . 1983. lrla'i nu'i f ì sh-pass report . unpubì i shed manuscrì pt.New Zealand Steel Mining Limited.

l'lai kato Va1 I ey Authority 1983. Report f rom the stand'i ng tri bunal to thel"laikat'o Va1ìey Authority as the Regìonal Water Boand fon jts meetingof 23 March 1983. in nespect of wat,er rìght applications fromNew Zeal and Steel Mi ni ng Li m.ited.

[,1e1'ls, R. r976. The -b'iology of grey mullet in Lake waah.i and thel.laj kato R'iven. unpubl'ished MSc thes'is, unì vers jty of wai kato.

47

fì sh-pass water intake, N.Z. Steel MiningAPPTNDIX I.

Slot

Water intaketo fish-pass

F'ish box tr'ap forLtd., Taharoa.

+ Box trap

Box hook

Hoop for padlock

for box hook

Removable bottom (a sliding tray)to empty catch

48

APPENDIX II. Gill net sample s'ites, mesh s'izes, and fleet 'lengths.

tr N.z. steetMining Limited

174" 44E

Mesh si zes of gì 'l I nets and I engths of f I eets

19 78 1984

Fleet 1 40 mm, 50 mm,85 mm 110 mm, 115 mmTotal length 100 m

Fleet 2 55 mm, 85 mm, 85 mm, 110 mmTotal length 80 m

Fleet 3 60 mm, 110 mm, 110 mmTotal length 60 m

Al I nets 20 m

40 mm, 50 mnr, 75 mm, 100 mmTotal length 80m

50 mm, 75 mm, 90 mm, 100 mmTotal ìengt,h 110 m

55 mm, 65 mm, 90 mmTotal 'length 150 m

20 m and 50 m net 'lengths

FISHERIES ENVIRONMENTAL REPORTS

1. l{ing, S.J. 1978. Fish species in the lower Waitaki River and tributaries. 14 p.

2. Davis, S. 1979. Fish and fishery val-ues of the Rakaia River: a preJ-iminary report. 55 p.

t. Docherty, C. L979. Submission on the fish and fishery requirements of the Hurunui River. 19 p.' 4. Unwin, M. 1980. A recreational survey of the 0rebi River, Southland: November 1974 - April 1975. J6 p.

5. Davis, 5. 1980. Submission on the proposed BalmoraL irrigation scheme. l8 p.

6. Iling, S.J.1979. Fish species in the upper Waitaki lakes and rivers. l0 p.

7. Striekland, R.R. 1980. Fisheries aspects of the l{hangamarino Swamp. 37 p.

8. Graynoth, E., Pierce, L.A., and lling, S.J. l98l. Fisheries aspects of the Lower Waitaki power scheme: anassessment of the impact of various deveJ-opment options on the fish stocks and fisheries. 72 p.

g. Glova, G.J., and Davis, S.F. 1981. Submission on the proposed Luggate,/Queensberry hydro-electricdeveloPment. 19 P.

10. McDowaII, R.M. 198I. CommerciaL production of quinnat salmon in New ZeaLand waters - background papers. 55 p,

11. Rowe, D.K. 198I. Fisheries investigations in the Motu River. 46 p.

12. McDowall, R.M. 1981.. Freshwater fish in Fiordland National Park. 3f p.

l). HabJ.ous, C.M.,StancLiff,4.G., and Thornton, B.K. 1982. Trout spawning runs in the Mary Burn' 1980. 14 p.

14. Cudby, E.J., and Strickland, R.R. In prep. The Manganuioteao fishery.

15. Stancliff,4.G., Hablous, C.M., and Thornton,8.K.1982. Effect of spillway discharges on the TekapoRiver. 24 p.

L6. McDowaLL, R.M. 198r. A listing of Minietry publ-icabions on freshwater fish and fisheries. 92 p. (2nd Ed.)

17. Teirney, L.D., Richardson, J., and Unwin, M.J. 1982. The relative value of South Canterbury rivers ÈoSouth Canterbury anglers: a preliminary report. 46 p.

18. Bloomberg, S., Stancliff, A.G,, and Thornton, B.K. I9Br. AngJ.ing in the upper Waitaki catchment.LgS0/81season. I7 P.

19. Teirney, L.D., Richardson, J., and Unwin, M.J. L982. The relative vafue of Waitakl VaIIey rivers to l{aitakiValley angJ-ers: a preJ.iminary report. 46 p.

20. Davis, S.F. 1982. Submission on the proposed Maitai water suppJ.y dam. 28 p.

2L. Teirney, L.D., Richardson, J., and Unwin, M.J. 1984. The re.Lative value of rivers in the Taranaki regionto Taranaki, Hawera, and Stretford anglers. 90 p.

22. Richardson, J., and Teirney, L.D. L982. The l{hakapapa River: a study of a trout fishery under a modifiedflow regime. 7I P.

. 2t. Eldon, G.4., Davis, 5.F., and Unwin, M.J. 1982. Submission on the Ashburton River water allocation pJ.an. )2 p.

24. StrickLand, R.R,, Teirney, L.D., and Cudby, E.J.1982. Submission on the ltlanganui River flow managementPlan. 27 P.

25. Bonnett, M.L., Davis, S.F., and Unwin, M.J. L982. Submission on the value of the Ashley fishery resources.J6 p.

26. Jellyman,0.J., Davis, S.F., l{ing, S.J., and Teirney, L.D.1982. Fish stocks and fisheries of the AhuririRiver sYstem. 84 P.

27. Eldon, G.A. 1982. Submission on the environmental implications of wetland use and management. 6 p,

28;, Teirney, L.D., Unwin, M.J., Rowe, D.K., McDowall, R.M. and Graynoth E. .1982, Submission on the draftinventory of wild and scenic rivers of nationaf importance. L22 p.

29. Jellyman,0.J., and Unwin, M.J.1982. Submission on Southl.and United Council Regional Energy Plan. 9 p.

)0. Eldon, G.A., and Greager' A.J.1981. Fishes of the Rakaia Lagoon. 65 p.

)ì. Jellyman, D.J., Kelly, G.R., and Unwin, M.J. 1981. Submission on the fish stocks and fisheries of theBuller River sYstem. 50 P.

)2. EJ-don, G.A. 1981. Submission on the Rotokino Swamp drainage scheme. L2 p.

1). Davis, S.F., Eldon, G.A, Glova, G.J. and Sagar, P.M. 1981. Fish populations of the lower Rakeia River. 109 p.

14. Strickland, R.R.198). Development proposals affecting future freshwater fisheries investigations inNorthland. 20 P'

)5. Unwin, M.J.r and Davis, 5.F.198r. RecreationaL fisheries of the Rekaia River. 110 p.16. Sagar, P.M. 1981. Benthic invertebretes of-the Rakaia River. 59 p.J7. Richardson, J., Unwin, M.J.r and Teirney, L.D. 1984. The relative value of Marlborough rivers to New

Zealand anglers. 5I p.

38. Trought, G.J.T, 1984. ResiduaÌ flows in the upper Ohau River. 27 p.59. Cudby, E.J. 1984. Fishery aspects of the Wairehu Canal hydro-electric scheme. 28 p,40. Richardson, J., Teirney, L.D., and Unwin, M.J. 1984. The relative value of t{ellington rivete to New Zealend

anglers. 7J p.

4J.. Jellyman, D.J. 1984. RecreaÈional use of the Ahuriri River, LgBZ/9r. 47 p.42. Richardson, J., Unwin, M,J., and Teirney, L.D. 1984. The relative vafue of Hawkers Bay rivers to New

Zealand anglers. 69 p.

41. Davis, S.F.1984. Recreational use of the Rangitata River, I980/8I. 57 p.44. McDowall' R.M. 1984. Escape of grass carp from the Aka Aka-0taua drainage system. 67 p.45. Richardson, J., lJnwin, M.J., and Teirney, L.D. 1984. The relative value of Nelson rivers to New Zeeland

angLers. 75 p.

46. JeJ.lyman, D.J. 1984. Distribution and biology of freshwaÈer fieh in the Clutha Rive¡. 69 p.47. McDowallr R.M. 1984. The status and exploitation of non-salmonid exotic fish in New Zealand. 6l p.48. Richardson, J., Unwin, M.J., and Teirney, L.D. Ì984. The relative vslue of Otago rivers to New Zealand

anglers. 79 p.

49. Mitchellr C.P. ì984. The Lake Poukawa traditional eel fishery: problems and suggestions for a managementstrategy. 17 p.

50. Teirney, L.D., Unwin, M.J., and Richardson, J. 1984. The relative value of Southland rivers to New Zealandanglers. 90 p.

5I. Saxton, B.A. f985. Trout in the lower l{aikato River. 22 p.52. Hicks' B.J. 1985. Potential. effects of hydro-electric development on Èhe fieh and fisheries of the

Rangitikei River. 55 p.51. Power, G. In press. A method for estimating potential insect availability at the surface of rivers.54. Penlington, B.P. 1985. The reinbow trout fishery in Lake Ototoa. 40 p.55. Strickland, R.R.1985. Distribution and habitats of fishes in the Mohaka River. 86 p.56. EJ.don, G.4., and KeJ.ly, G.R. 19S5. Fishes of the t{aimekariri River estuary. 59 p.57. Bonnett, M.L., and Docherty, C.R. 1985. An aesessment of trout st,ocks in the upper Hurunui River. 14 p.58. Rowe,0.K., and Schipper' C.M. 1985. An assessment of the impact of grass carp (Ctenopbql¡Sgdg!_i!91þ)

in New Zealand waters. I77 p.59. Richardson, J., Teirney, L.D., and Unwin, M.J. 1.985. The relative value of Auckland rivers to New ZeeLand

saLmonid anglers. 8l p.60. Mainr M.R.r Nicoll, G.J., and Eldon, G.A. In press. Distribution and biology of freshwater fishes in the Cook

River to Paringa River area, South l{estland.61. Whiting, R. In press. l{ater-baeed recreation on the lower Clutha River.62. Bonnett, M.L. In press. Fish and benthic invertebrate populations of Ehe Rangitata River.