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New ZealandFreshwater Fisheries Report

No. 103The kahawa¡ f¡shery

at the Motu River mouth.

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MAFFishNew Zealand freshwater fisheries report no. 103 (1988)

New Zeal and Freshwater Fjsheries Report No. 103

The kahawai fishery

at the Motu Ri ver mouth

by

B.P. Penl i ngton

Freshwater Fisheries Centre

MAFFi sh

Rotor u a

December

1988

New Zealand freshwater fisheries report no. 103 (1988)

This report is one of a serìes issued by the Freshwater F'isheriesCentre,'MAFFish, on ìssues related to New Zealand's freshwaterfjsherÍes. They are jssued under the followìng crjteria:

(1) They are for ljm'ited circulat'ion, so that persons.andorgänisatìons normal ly receivìng.MAFFi¡h puþl jcationsshõuld not expect to iecejve copies automatically.

(2) Copies w'iì 1 be ìssued free onìy to of -ggnisations to wh jch the

reþort is d'irect'ly relevant. They wjll be 'issued to otherorganì sat'ions on request.

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willbereprjntedandchargedforatthenewrate.

(4) 0rganisat'ions may apply to_the librarìan to be put on the

ruíliné-iìit-to iecäivä all reports as thev are published'Rn .invõice wi I I be sent with each new publ icat jon.

NE[,J ZEALAND FRESHI,/ATER FISHERIES REPORTS

ISBN O-477.08L7I.I

The New Zealand Freshwater Fjsheries Report series.ôñtinues the Fìsheries Envjronmental Report series.

Enquiries to:

The LibrarianFreshwater F'i sheries CentreP0 Box 8324Riccarton, Chr.i stchurchNew Zeal and

MAF Fish


1.

2.

3.

4.

Summary

5.

I ntrod uct'i on

Biology of Kahawai

Study Area

Methods

Results

Di scussi on

6.1 Review of theSurveY

6.2 Maori AsPects

Conclusions

Acknowl edgments

Li terature C'i ted

CONTENTS

lgBL Motu R'iver Kahawai F'ishery

of the Motu R'iver Kahawai Fishery

Page

4

4

5

8

10

I2

16

19

6.

24

24

7.

8.

9.

6

9

13

l4

I4

4.

1.

2.

3.

6.

7.

F I GURES

Kahawai (ArriPis trutta)

Motu Rjver estuary, show'ing locatìon of nettjng sites

Length-frequency djstribution of kahawai caught at the

¡'lótú niver'mout-h from January to April 1983

Percentage of kahawa'i with gonad development at stage.3o; il;uiãr on the Ñìrolskv õcale, November 1982 - Apriì19 83

Percentage of kahawaj that contained food items jn the'irstomachs, November 1982 - April 1983

Freshwater pìumes off the Motu River mouth

Freshwater p1 ume velocitjes at various dìstancesf rom the Motu R'iver mouth

Mean dai'ìy counts of anglers per week and mean

"ãðfly-caich of kahawai-at the Motu River mouth'

iunuuiv - AprìI 1982 (after Ritchie et al' 1982)

2I

24

i6

T7

5.

8.20


4

SUMMARY

A study of kahawai aggregations at the mouth of the Motu Rjver was

carnied out from November 1982 to Aprìl 1983. The prìncìpal objective

was to determine the factors ìnfluencing these aggregations. It was

concluded that the fjsh gathered during'late summer spawning migratìons.

The kahawai fishery at the rjver mouth is an ìmportant traditional

fishery to the people of the district. A total of 833 people was

observed fishing there during a 12-week survey'in summer and autumn

1982, w j th 3270 f i sh be'i ng caught by 506 peopl e i nterv'iewed .

1. INTRODUCTION

The potentia'l for hydro-electric development of the Motu River has

been investjgated on an irregular basis since 1956. In 1977,

investigatìons were resumed by the Mìnìstry of Works and Development

(M[JD). To assess the impì ìcat'ions of hydro development for the

fisherìes, the Freshwater F'isheries Centre (FFC) at Rotorua, together

with the Department of Internal Affairs, injtiated a joint fisherjes

survey of the Motu R'iver. The aim of the study was to identjfy the maìn

freshwater fish populations jn the river and'its trìbutaries. The

results of the survey (Rowe 1981) r^lere used to predict the poss'ible

effects of hydro-el ectri c devel opment on the fi sh popul at'i ons i n the

¡iver, assum'ing that power generation would alter river flows and create

barriers to fish movement.

Rowe (iggl) considered that hydro-electric development could affect

the kahawa'i fjshery at the mouth of the Motu River. The fishery isbased on large schools of kahawai whjch congregate near the river mouth

duri ng I ate summer. If these concentrati ons of fi sh depended on

"biologìcal" factors associated with the ecology of the river (e.9.,

upstream migratìons of smelt or Galaxias), then the kahawai fishery

could be affected by hydro-electric development.

To assess the effects that hydro-electric development could have on

the kahawa'i fishery, two studjes rarere carried out. The princ'ipaì

objectives were:


5

1. To determjne the factors causing kahawa'i aggregatìons at the river

mouth (i.e., why do kahawai congregate there and sometimes enter the

ri ver?) .

If the 'i nfl uenci ng factors coul d be defj ned, then j t mi ght be

possìble to reduce any detrimental effects from hydro-electrjc

development of the rjver. Most studies on kahawai have shown that

the fish enter estuaries to feed. Thus the initjal objectìve of

th'is study was to determine if the kahawaj congregated to feed, and

to list the principal food species. The other object'ives were to

determi ne:

(a) whether the sj ze and frequency of kahawa'i aggregations were

af f ected bY t i de he'i ght ;

penetrated the river beyond the estuary;

(d) whether the kahawai had any external parasites;

(e) whether a plume of river water could affect the migratìon of

kahawai.

2.Toassessthesìze(jntermsofnumberofpeoplefjshìngandnumberof fish caught) and importance of the recreat'ional kahawai fìshery.

Thjs second objectjve was carried out by the Environmental Stud'ies

Un'it of Waikato Unìversìty, after representatjons by FFC and the

Motu R.iver Ecology working Party of MWD. The results were reported

by Ritchie et al. (1982) and are summarìsed briefìy jn thìs report,

together with some comments on Maorì aspects of the fìshery.

2. THE BIOLOGY OF KAHAWAI

(b) whether kahawa'i

ôgê, size, sex'

(c) whether kahawa'i

Kahawaì (Arri Pì s trutta)New Zealand and Austral'ia.important speci es known as

southern Austral i a from Perth

aggregatì ons were sel ectì ve w'i th respect to

or maturì ty;

(Fig. 1) are pe'lag'ic marine f ish found jn

In Austral'ia, they are a commercì al ly

"Austral 'i an sal mon " , and are found 'i n

to New South Wales. In New Zealand, they


FIGURE 1. Kahawai (Arri pi s trutta) .


7

are increasing jn commercjal importance (4900 tonnes were harvested in

1933), and al so support s'i gnìf i cant non-commercì al , recreatjonal

fisheries in some areas.

Litile js known of the bioìogy of kahawai jn New Zeaìand, aìthough

they have been wel I studied 'in Austral i a. some aspects of the bìo'logy'

notably movement and growth, appear to dìffer between the two countries

(G.D. James pers. comm.).

Eggleston (1975) aged kahawai usìng otol'iths and scales, and found

that they mature at 35-40 cm (at 4-5 years of age) and live for a

maxjmum of 22 years (60 cm). He consìdered them to be a long-ììved,

sì ow-growi ng fi sh, and , therefore, to be more susceptì b1 e to

over-f ishì ng than short-l i ved, f ast-grow'ing spec'ies '

Kahawai Spawn at sea during Summer and autumn, and the eggs are

planktonic. No d'istinct spawning areas are yet known jn New Zealand,

although some have been observed in Austral'ia. The eggs hatch 40 hours

after fertiììsat'ion, and the larvae reach a length of 4 mm after four

days (Stanley and Malcoln 1977). The iuveniles ()50 mm 'in length) later

enter bays and estuaries, which act as nurserjes where young kahawa'i

feed on small fish and crustaceans (Healy 1980).

Estua¡ine f ish studies by tiebb (1973), Kjlner and Akroyd (1978), and

Healy ( i9g0 ) have shown that adul t kahawai enter I arge estuari es

throughout the year to feed. Fì sh, parti cuì arìy ye1 ì ow-eyed mul I et

(Aldnichetta forsteri) and flounder (Rhombosolea spp'), and crabs are

the majn food 'items. In the Motu River, kahawa'i occas'ionally move up

into fresh water du¡ing winter and spring to feed on mìgratìng whiteba'it

(Galaxias spp.) (P. Powell pers. comm.).

Feeding studjes in tiell'ington Harbour (Baker L97L) found that fjsh

compri sed 51% of the d'iet of al I kahawa'i exami ned. Anchov'ies (Engraul'is

austral j s ) compri sed 57% of the total fi sh eaten, and crustaceans

accounted for v j rtual ly the rema'i nder of the dì et. Kahawa'i are

opportuni stj c carni vores, feedi ng on the most readi ìy avaj I abl e food,

and their diet varies little between seasons.

Kahawa'i are found throughout New Zealand, from North Cape to Stewart

Island, wìth major concentrations jn the Bay of Plenty, Tasman Bay, and


8

off the Kaikoura coast. Large schools of kahawaì have

from around the New Zeal and coast throughout the year

1981), varying in density and in sjze, from a few hundred

fjsh. In January I978.- most schools recorded conta'ined

fì sh.

been recorded

(Habjb et al .

to over 10 000

1-40 tonnes of

Large numbers of school ì ng fj sh have been tagged ( James et al .

Ig82), with the ajm of using tag recoveries, together with aerjal

sì ght'i ngs, to estimate the si ze of the New Zeal and resource. The

taggìng studies have shown that kahawaj move considerable dìstances,

w'ith distjnct seasonal movements. In some areas, the schools of fjsh

move inshore during winter and summer, and large schools may congregate

around river mouths for variable periods before moving away.

Recreatjonal fishermen have provided up to 40% of the tag returns, which

indicates that the recreat'ional kahawa'i fishery around New Zealand js

more significant than was previously thought. In western Australìa,

recreatjonal fishermen accounted for 22% (1000 tonnes) of the kahawai

catch .

3. STUDY AREA

The Motu Rjver lies 'in the eastern Bay of P'lenty (Fig. 2). It is

the ì argest ri ver in the region, and the fourth I argest jn the

North Island jn terms of mean flow; mean annual discharge js 89.3 m3ls

(range 5-3745 r37s). Most of the catchment is beech forest (Nothofagus

spp.). The steep topography and lack of water storage results jn rapìd

runoff and large peak flows. The riveris renowned for its wjld and

scenic character, and 'is well used by rafters, canoeists, iet boaters,

and trampers (R'itch'ie et al . 1982). However, the greatest recreational

use occurs jn the lower reaches, especially the estuary' where kahawai

fi shj ng takes p1 ace.

Estuarìes, as defined by Barnes ('in Eldon and Greager 1983), are

areas of salt or brack'ish water, separated from the adjacent sea by a

low-ly'ing barrier of sand or shìng1e. Their exchange of water js 'large

coripared to thejr volume, and they have a relatively large mouth. The

I ower Motu R j ver can be cons'idered a smal I estuary accord'ing to th i s

descriptìon, because 'its water changes are 'large, and jts sal ìnìty


FIGURE 2. Motu Rjver estuary, showjng location of nettjng sites.


10

f I uctuates cons'iderably. tlJìth an area of 0.56 km?, it js smal I

compared to other estuaries that have been stud'ied (Avon-Heathcote (7.8

fm2) Webb 1972; Porirua-Pauatahanuj (8 km2) Heath 1976), or to others

in the Bay of Pìenty (e.g., Qhiwa Harbour (24 km?) Richmond et al '

1984).

The Motu estuary consìsts of three interconnected ìagoons, up to 3 m

deep, formed by shingìe banks (Fjg. Ð. These banks are unstable and

constantly ìn motion; they change extensively durìng floods because of

the extreme flows and the lack of stab'i'lìsing vegetation. The

substrates are sandy, but sjlt builds up in pondìng areas after periods

of hìgh flow. The s'i lt is mainly brought down into the lagoon and

deposited there during floods, and jt ìs gradually flushed out by tjdal

movement.

There is litile cover or refuge for large fish ìn the estuary.

Th.is, combìned with the large peak flows and jnstab'i1ity of the lagoons'

limits the number of fjsh that can reside'in the estuary' As a result'

most of the specìes present are transitory, varyìng according to season'

tide, and rjver condition, and depend on the ¡iver ma'inly for food'

Those observed in the estuary were kahawai (Arripìs trutta), yelìow-eyed

mul I et (Al drj chetta forsteri ) , bl ack fl ounder (Rhombosol ea reti arj a) ,

grey mullet (Mugil cephalus)' triple fin blennìes (Tripterygjon sp')'

i nanga

par0re

(Galaxias maculatus), common bully (Gobjomorphus cotidianus)' and

(Girella tricusPidata).

Most of the fish specìes found in the upper reaches of the river

al so spawn 'in, or mi grate through, the estuary at some stage of the'ir

life cycle. These are the koaro (Galaxjas brevipinnis), banded kokopu

(Gal axj as fasci atus) , short-jawed kokopu (Gal axi as postvecti s) ' bl ue-

gì'l 'led buì ìy (Gobi omorphus hubbsì ) , red-f i nned bul ly (Gobi omorphus

huttonì ) , torrentfj sh (Cheimarrj chthys fosteri ) ' ìong-fi nned eel

(Angui I I a dieffenbach'i ), and short-fj nned eel (A' austral j s ) (Rowe

1981 ) .

4. METHODS

From November 1982

using giìl and trammel

to Aprì ì 1983, sampì es of kahawa'i were taken

nets, or were caught from the beach w'ith lures


11

cast on handl'ines. The mesh sizes of the gìì'l nets used were 50, 100,

115, and L25 mm. Use of the trammel net (100 mm internal mesh) was

advantageous because it could catch fjsh from 250 g to 3 kg.

Most of the nets were pìaced in the estuary (Fig.2), and several

were set at sea iust beyond the river mouth. At low tìde' few areas

wì thjn the estuary were suffi cientìy deep for the nets to be set

effectìvely. Nets were set at varìous distances from the mouth of the

river to determine how far kahawai had moved upstream. 0n 4,5,6,18,19, and 20 January 1983, all nets were checked every 3 hours between

0600 h and 2000 h, to assess changes in catch rate w'ith tide heìght' and

to determine jf kahawai had rema'ined in the estuary at ìow t'ide, or had

entered fresh water during the summer period'

All fish caught were we'ighed and measured, and the'ir sex' gonad state

(Njkolsky scaìe, as descrìbed by Ricker 1971), and stomach fullness were

recorded. Stomachs were opened and inspected visua'lly, and the'ir

fullness was assessed subjectively. Fjsh were exam'ined externally for

macroparasites or assoc'iated damage'

The extent of the r.iver's freshwater plume was measured by releasing

a ser.ies of current drogues. These were pl astì c dri nk'ing straws , 2L0

mm long x 7 mm diameter, sealed at both ends with paraffin wax' and

weìghted at one end by 13 pìeces of No.3 lead shot' This ensured that

the drogues would remain 669' submerged, to reduce the effect of wìnd,

and that they wou'ld stay upright. The drogues were placed ìn groups of

200 at the centre of the river mouth. Their progress and distribut'ion

were pìotted by triangu'lation, whjch gave the shape and velocjty of the

plume. The procedure 1aas repeated several t'imes throughout the tìdal

cycle at each of the rìver's outlets. conductiv'ity measurements were

made at various pojnts durìng the progress of the drogues, to assess the

extent of fresh and salt water mix'ing'

To examìne the possjble effect of fresh water on external parasites

of kahawai, five fish were placed ind'ividually in 0.5 m3 of fresh water.

After a period of 20 m'inutes, g j I I sect'ions and mucous scrapi ngs were

taken for examinatjon under a stereo mìcrosCope, for evidence of

ectoparasjtes. Gill sections and mucous scrapìngs were also taken from

another fi ve fi sh that had not been subjected to the fresh water

treatment.


T2

RES UL TS

During the 21 days spent in the field over the sampling perì0d,400

kahawai were caught and examined, and 85% of these were ìonger than

35 cm (Fig.3). The mean ìength was 55 cm, and the ratio of males to

females was 40:60. Most of the fjsh were caught in trammel nets, and

the fact that none were caught in the 50 mm net orin a seine net (10 mm

mesh) ìndicates that few or no small fjsh were present durìng the study

perìod. It was consìdered that these two methods would have'ind'icated

the presence of juveni le kahawai.

The gonads of male and female kahawaj both jncreased 'in maturity

(Nikolsky scale) between November 1982 and m'id February 1983 (Fig. 4).

In November, less than l"Á of kahawai examined had gonads whjch had

matured to stage 3 or greater. The February sample contained the

highest proportion of maturìng fìsh, with 65y" be'ing at stage 3 or

greater, and 43% of these were at stage 4. The comparable figures were

56% and 13% in late January, and 34% and 12% in early March. In Apri'|,

the percentage of gonads deve'loped to stage 3 or greater was only 4%.

However, ìfl thj s sample, 75'Á of the gonads were consjdered to be

resorbing; the degeneratjng gonads were decreasing 'in weight and size,

and the cond'itjon of the sexual products was regress'ing. This was

generalìy apparent from the uneven sjze of the eggs, and from the ìarge

ovaries whjch were mottled jn colour and unevenly fjlled. The sample of

kahawai caught ìn Apriì also contajned a h'igh proportion of fish showing

sì gns of external damage to the eyes, tai I s, and gi I I covers, and

jnternal deterioratìon, usual 1y of the liver.

Examination of the stomachs showed that from November L982 to mid

Aprì I 1983, the percentage of f i sh wi th food j n the'i r stomachs decl 'ined

(Fig. 5). In November, 50% of the kahawaì stomachs examined contained

traces of food, but by February, only 28% d'id so, and thìs declined to

I% by Apri'l. The main food jtem was the remains of fish whìch had been

dìgested beyond'identificat'ion. Identjfjable foods jncluded anchovies

(Engrauljs australis), yellow-taìl (Seriola ìalandi ), sausage worms

(Ech'iura sp.), freshwater eel (Anguilla spp.), triple-fin blennies

(Tripteryg'ion sp.), and the common freshwater bully (Gobjomorphus spp).

5.


N=417

SPAWNERS

40

LENGTH (cm )

FIGURE 3. Length-frequency distribution of kahawai caught at the Motu River mouth from January to Aprì'l1983. (Definition of age and spawning size classes is after Eggìeston 1975.)

5+4+3+

u30zTUÉ.lOoo

b20OzlJ-lloUJÉ.lL 10


50

N=198

MAR APR

GONAD DEGENERATION

1O

t!q40t-zLUogoÉ.tufL

20

NOV JAN

MATURING

JAN FEB

SPAWNING

MAR

PERIOD RECOVERY

N=18ó

MAR APR

food items in their

FIGURE 4. Percentage ofgreater on the

NOV JAN

kahawaj with gonad development at stage 3 orNj kol sky sca'le, November 1982-Apri I i983'

\oo\

r.rJ 30(tt--zLtJo20É.ul(L

10

Percentage of kahawai that containedstomachs, November 1982-Apri1 1983.

MAR

FIGURE 5.


15

The decl i ne 'in the occurrence of food 'items i n the stomachs of

samp'led f i sh corresponded w'i th an j ncrease i n gonad maturi ty, and the

decl'ine contjnued after the mean maturity of the sample started to drop

(Fìgs.4 and 5). The pattern of occurrence of food'in the stomachs js

possìbly assocjated wìth pre-spawning m'igratory behav'iour and with the

poor condit'ion of kahawaì caught in the post-spawning period. Hoar

(Lg57) stated that, for many fìsh specìes, sexual maturat'ion involves a

movement of nutrìtive material, including fats and proteins, from muscle

to gonads. Such changes are frequently assoc'iated with a decline ìn

feeding rate. The schoof ing behavjour of kahawai, coupled wìth the

reduced feedìng and'increasìng maturity of the gonads, suggests that

their congregat'ions are associated w'ith spawning mìgrations. The fact

that anglers use fìsh-like lures does not necessarjly indicate that the

fish are feeding, as kahawai schools are very dense, and jt js possible

that the fi sh w'i I I stri ke at smal I brì ght obiects wh i ch ' annoyr them,

even when not feeding.

The kahawai were examined for external parasites because it was

consjdered possìble that they enter fresh water to reljeve themselves of

external parasites prìor to spawnìng. Bardach et al. (1972) reported

that jmmers'ion of farmed yelìow-taiì (Seriola quinquerad'iata, a pelagìc

mari ne specì es ), 'in fresh water for 3 mi nutes at 26"C, or for 5 minutes

at 16"C, removes infections of the flat worm Bendenia. Hewitt and Hine

(IglZ) listed three external parasìtes of kahawai, as well as eight

jnternal parasites recorded jn the literature. The external parasìtes

were Gonopl asi us truttae, (Monogenea), and two ì sopods, Codonoph'i I us

.imbrjcatus, from the mouth and throat, and Nerocjta orbignyi, from the

body.

External paras'ites were not observed ìn the gììl sectjons or mucous

scrapings of kahawai from e'ither the freshwater-treated or the untreated

sampìes. Thìs ìndicates that kahawaj do not congregate at rìver mouths

to remove parasites.

Velocity measurements of the freshwater plume from the Motu R'iver,

determined from drogue movements, showed that the current produced was

detectable at a d'istance of 0.75 km from the river mouth. Fjgure 6

shows a plot of the freshwater discharge p'lumes from both the western

and eastern mouths of the river, at full tide and at a dìscharge of


16

FIGURE 6. Freshwater pìumes off the Motu Rjver mouth. Solid ljnesshow the posìtion of drogues one hour after release.Dotted lines are the assumed shapes of the plumes. Arrowshows the direction of the coastal current.

82 n3/s. The velocity of water in the pìume ranged from 2.20 n/s atthe river mouth, to 0.09 m/s at a distance 0.75 km seaward from themouth (Fì9.7). The pìume of fresh water moved out across the surface

of the salt water, forming a halocl'ine between the two mouths. The

freshwater layer was 50 mm deep at a djstance of 0.75 km from the mouth.

The freshwater temperature was 11.5oC, compared to a sea temperature of16.7"C.

6. DISCUSSION

Kahawa'i are part of a popular recreational fishery at the mouths ofmany New Zealand rivers (Davjs 1979, Strickland et al. 1982, Bonnett

et al. 1982, Eldon and Greager 1983, Strjckland 1985, Eldon and Ke1'ly

1985, Bonnett 1986, Pierce 1987). Their fightìng quality is well known


ãL

oo(¡)cr 2.oL

oo(t,q)

Po)

5l-OoJt!_> 1.Ol-zulÉ.É.lO

0'05m/s CRITICAL VELOCITY BY SMALL FISH

150 300 450 600

DISTANCE FROM RIVER MOUTH (metres)

FIGURE 7. Freshwater pìume velocitìes at various distances from the Motu River mouth.detect'ion by smal I f ish 'is from Mitchel ì in press. )

750 (850m)

(Critjcal velocìty


and they provìde

1979, Je1'lyman et al . 1983, El don and Keì 1Y 1985) .

18

good sport on a rod or hand I i ne (Wi ng 1978, Dav'is

In the South

often fi shed for when the salmon are not runnì ng

Although kahawai are not usually sought after as an

known that a group of anglers travels from Dunedjn to

Waitaki Rjver soleìy to catch this species for food

comm. ).

I sl and, they are

(Docherty 1979),

eating fish, 'it isthe mouth of the

(1.4. Pìerce pers.

Kahawai gather in large schools around the Motu and other ìarge

rjvers durìng late summer. V'isual observation of these schools at the

Motu R'iver mouth showed that they were generally travellìng from south

to north. They approached the mouth and spent between 15 minutes and

t hour either jn the plume of fresh water or slightly to one side. At

low t'ide, no kahawa'i were observed or caught jn the estuary. At high

tjde, however, some d'id enter the estuary, but did not penetrate beyond

the i nfl uence of the sal t water, aì though mul I et and parore were

observed 'in f resh water . However, kahawai have been seen several

kjlometres upstream jn some rjvers (Eldon and Keì1y 1985), and a few

jndìvidual kahawai have been observed in the Motu River between Aprìì

and November (P. Powell pers. comm.). It is thought that they enter

fresh water occasi onal ly, possi b'ly when feedì ng, and especi al'ly when

feeding on whitebait (Galaxias spp') (McDowall 1978)'

Egg'leston (1975) considered that kahawai atta'in a m'inimum'length of

35 cm at f j rst spawn i ng. Because 85'/" of the f i sh exam'ined f rom the

Motu Were 'larger than th'is, these were obviously mainly adults.

Samples ind'icated that the kahawaj were approaching fu'll maturity in mid

February and that the proport'ion of fjsh with maturjng gonads decreased

afterthistime(Fjg.5).Aìthoughonlyonefjshwithfullyripegonads was caught, ìt appears that kahawai spawn at the Motu Rìver mouth

during February. It is suspected that several marine species,'including

kahawai, approach full maturity quickly over a perìod of only a few

hours before the eggs are released (G.D. James pers. comm.), and thjs

could account for the low catch of fully ripe females'

In Australia, kahawaj are known to swim towards their spawnìng area

against the coastal current (M. Walker pers' comm')' In the eastern

Bay of plenty, the coastal current runs from north to south (Rjddell

19g0), and the observed kahawaì schools travel on the surface against


19

thìs. McKeown (1984) suggested that fish use thejr lateral ljne

Sensors, or other organs, in conjunction wjth other means, to detect

currents'in the open ocean where no reference po'ints exist. It'ispossible that kahawai are attracted to the Motu River by the current of

rjver water enterìng the sea. The rjver's plume veloc'ity 0.75 km from

the river mouth was 0.09 m/s. Mitchell (in press) determjned that the

minjmum water velocity that native freshwater fjsh could respond to was

0.05 m/s. If kahawaj respond to a sjmilar minjmum velocity, then

extrapoìation of the curve in Figure 6 would suggest that they could

detect the Motu R'iver current at a distance of 0.85 km offshore, given a

niver dìscharge of 82 m3/s.

A survey of coastal kahawai fi sherì es (FFC unpubl i shed data)

indicated that schools of kahawai are found near rivers and estuaries

that have signìficant discharges of fresh water. Those estuaries which

discharge ljttle fresh water appear to attract few kahawai. The

necessìty of a flow of fresh water to attract kahawa'i to a rjver mouth

was demonstrated by the d'iversion of the Kajtuna River, Bay of Plenty.

The Maketu Estuary, ìnto whìch the Ka'ituna River formerly fìowed, had a

good kahawai fishery. However, when the rjver was djverted to bypass

the estuary, the concentrat'ions of kahawa'i di sappeared, and a new

fishery began at the mouth of the diversion channel.

It is likely that the late summer spawn'ing migrations of kahawa'i are

attracted to the Motu River mouth by the outflow of fresh water,

a'lthough the mechanjsm of thjs attraction js sti I I unknown. Kahawaj

appear to respond to an environmental stimu'l us, such as the water

current, whìch attracts them towards their spawning areas. They are

present at the river mouth for a ljmited period before resuming thejr

coastal m'igrations. They appear to be attracted onìy temporaflily by

the flow of the river as ìt jntercepts theìr mjgration pathway.

6.1 Revjew of the 1981 Motu River Kahawa'i Fishery survey

The kahawai fishery at the Motu Rjver mouth js cons'idered to be an

important regìona1 resource. Hydro-electrìc development in the Motu

catchment could modify the flow regìme of the river, and either d'irectly

o1indjrectly affect the kahawai fishery at the rjver mouth. Therefore,

aS part of a study of recreational use of the Motu River, the


20

Environmental Studies Unit (ESU) of l.laikato Universìty carried out a

survey from January to April 1982, to est'imate the sjze and use of the

kahawaì fishery. The foìlowing jnformation summarises the ESU report

(Ritchie et al. 1982).

The number of people seen fishing at the Motu River mouth was

recorded once a day during the survey period. The week'ly median of the

dai ly counts js presented 'in Figure 8. Extrapolatjon of these data

gives a m'inimum total count of 833 peop'le fishing during the 12-week

period. The greatest number of people fished durìng the last week of

January, and the numbers declined gradual'ly thereafter. Floods and

freshes during six of the surveyed weeks lowered the median daily counts

for those weeks. The number of people observed fìshìng was poss'ibìy

lower than the actual number fìshing, aS counts were made only once a

day, when the greatest number of people may not have been present'

JAN UARY

15

10

ØÉ.ulJ

É.qtll zfL

LLtolr É.LLUogffi2m\

lll2dz

Mean daily counts of anglers per week (dots), and mean

"ãðflV .uich of kahawai-(bars) at the Motu R1ver mouth,

iãñuuiv-Àp.il Ig82 (after Ritchie et al' 1982)'

FEBRUARY

FIGURE 8.


2T

During the 12 weeks of the survey, daily'intervjews of anglers were

conducted to obtain'information on the orìgìn of people fìshing, the

number of fjsh caught, and the amount of tìme spent fishing. 0f the 506

people jnterv'iewed, only 19.3Á lived in the local area (defined as the

area between, but not incl uding, 0potikì and Cape Runaway). Another

33% ljved in gpot'iki, and I4/" travelled from other places for a day's

fishing. 0f those jnterviewed, 33.71[ were staying away from home, and

85% of these came from within the area bounded by Tauranga, Hamilton,

Taupo, and Gi sborne.

The number of fish caught per person per day ranged from 0 to 60,

and the total weekly catch ranged from 10 to 1408. A total of 3270

fjsh was caught by the 506 jnterviewees. However, larger numbers of

fjsh were reputedly caught by individuals who were not interviewed.

During the Survey period, 'ìoca'l' peopìe spent an aVerage of 2.08

hours fishing, and caught an average of 4.17 fjsh per hour. Peopìe

from outside the survey area spent 2.65 hours fishìng, at a catch rate

of 2.24 fish per hour. Qveral1, each person on average spent 2.54 hours

fishing and caught 2.55 fish per hour.

The h'igher catch rate for local people, compared wjth that for

people from outsìde the area, was partly attributable to the local

peopìe mostìy us'ing hand Iines, wh'ich allow for a better 'feel' for the

fish. People from outsjde the area mainìy used surfcasting rods, which

tend to'lose,more fish than hand lìnes. Also important was the fact

that it was easier for the locals to be at the river when the fish were

present, whereas outsiders had to take pot luck.

6.2 Maori Aspects of the Motu River Kahawai Fìshery

Power (1849, in Best 1929) wrote of the kahawa'i :

"The'ir advent 'i s hai I ed wi th joy by both Maori and

wh'i teman greeted wì th shouts and cheers " .

The Motu Rjver was consjdered by Te Rang'i Hiroa (1926) to be famous

for its kahawaj fishery. He reported the main fjshìng method to be a

paua shell lure (pa kahawaj), rather than the dip or se'ine net used in

other areas . The I ure was a hook made from wood, w'i th pjeces of paua


22

and a line attached to it, wh'ich was cast out as far as possible jnto

the rjver mouth. The fisherman would then walk backwards, co'il'ing his

line as he went. The current caused the lure to spìn, and thus toresemble a small, slow-movìng fish. The same fìshing method js stjllused on the Motu today, although the pa kahawai has been replaced by a

modern version made of lead and paua shell, or by commerc'ia'lly-purchased

sea-trolììng 1ures.

Historical ly, 'legend has ìt that the kahawa'i were gifted to the

people of Maraenu'i, adjacent to the Motu, by Tangaroa, the god of the

sea, after the Maori people arrived from Hawaji. When Maraenu'i was

fjrst settled, one of the resjdents was Pou-Ma-Tangatanga, who had a

wife, 0hjnemotu, and a son, Hekopara. lllhen Hekopara went mi ssing,

Pou-Ma-Tangatanga searched for hjm unti I he was tol d to consul tTangaroa. Tangaroa admjtted that he had taken Hekopara for his own

purposes. 0n seeing Pou-ma-Tangatanga's grief, Tangaroa gave a gift to

pou-ma-Tangatanga and h'is peop'le. Tangaroa told Pou-ma-Tangatanga that

when the dust of the bracken fern flew, and the berry of the karaka

turned golden, a gift would be sent to the mouth of the Motu River.

Pou-ma-Tangatanga and hjs people could take as much as they wìshed until

the kowhai floods came to keep the river clean. (Kowha'i floods occur

'in late March, when jt rains in the headwaters, but 'is st'ill f ine on the

coast (8. Tawhai pers. comm.).) The gift would return each year to

commemorate the loss of HekoPara.

In 1900, a major catastrophe occurred at the river mouth. E'ighteen

chjldren and an elderly ìady were drowned'in the Motu, wh'ile crossìng ìn

a canoe to attend school at Oma'io. These chjldren aìways crossed on a

Sunday, stayed with relatjves during the week, and returned to Maraenuj

on the folìowìng Friday. The Tohunga of the R'ingatu fajth went into

retreat and prayed until all of the bodies had been recovered. Many of

the Maori people in the Te Kaha d'istrict, being members of the Rìngatu

fajth, observe Saturday as the Sabbath. To commemorate thìs tragedy,

kahawaì fishing js prohibited at the river on this day, and thispractì ce j s fol I owed rì gorousìy, even by non-Rj ngatu Maorj . The

kahawaj season is officjally opened on 1 November each year by members

of the Ringatu faìth, one of whom catches the first fjsh of the season.


23

At the Motu R'iver today, kahawaì are sti I I ìmportant as a

trad.itional food, and they are also'important socia'11y. In earl'ier

tjmes, they were economically'important to the people of the Maraenui

and Ta Kaha reg'ion. Cons'iderable prest'ige, or mana, ìs assoc'iated wjth

the quality and presentation of food. Du¡ing the kahawai season' the

host marae ìs expected to serve kahawai at any gatherìng' Fajlure to

do so w'ill result in a loss of respect for that host marae.

Before processed food became read'i'ly ava'i I ab1e, kahawa'i were an

important part of the di et for the peopl e of Maraenu'i and the

surroundì ng dj stri ct. Each famì 1y woul d travel to the ri ver, usuaì 1y

by horse, on the best fishing day'accordìng to their famì1y's fìsh'ing

calendar. Every famjly had one of these, whjch had developed over many

generations, and 'indi cated the best times and p1 aces for fi shing' A

large number of fish was caught and taken home for preserving' The

beì]y strip (pectoral fins to the anus) was often eaten by the fisherman

on the beach, as hi s ri ght. The boj led heads were regarded as a

delicacy, from which the women had fjrst choìce. The fish to be

preserved were cooked in a hangi before beìng left jn the sun for 3 to 5

days to dry, although they were taken jnside each nìght. (lntroduct'ion

of the European wasp caused considerable problems for the drying of the

fish.)Thedriedfish,knownaspawhera,wasveryhardandWasoftentaken'into the bush by hunters as a food supply. It was also steamed

over kumara and woul d swel I w'i th absorbed mo'i sture. It was then served

with the ma'in meal .

In recent times, pawhera productìon has ceased, and the fish are

botiled or frozen jf they are not eaten immediately. Large numbers of

fjsh are often caught specifical'ly for socìal gatherìngs such as tangìs

or huìs, where they are served either fresh or smoked' Several maraes

have buìlt their own smoke houses for this purpose.

Because the.ir survival has depended on food suppìies, the Maori have

consciously practised conservation jn all forms of food gatherìng' by

banning explojtation of depleted resources or those in poor conditìon'

The Ímportance of food supplies to the pre-European Maori is evident

from the many battles fought over food resources' Local Maori are

concerned about the di srespect for the Motu kahawai shown by the many

outsiders who leave part or al1 of their catch on the beach.


24

7. CONCLUSIONS

Large numbers of kahawai gather at the Motu Rjver mouth during latesummer, and these congregations sustaì n a fi shery of soci al and

hjstorical ìmportance to the people of the Maraenui and Te Kaha region.

They also contribute to the local tourist economy. Most of the fishare adults that are not feeding, but are approaching sexual maturity,

and may be part of a spawnìng migration. Kahawai are probably attractedto the river by the discharge of fresh water from the mouth, although

the reasons for thjs are not yet known.

It is recommended that, jf the flow of the Motu R'iver must be

reduced, it should be reduced as ljttle as possible durìng the summer

from November to March. Any loss of kahawai from the river mouth could

have serious cultural implìcatjons for the people of Maraenui and the

surrounding district.

8. ACKNOI,JLEDGMENTS

This work was made possìb'le by the ass'istance of R.R. Strickland,

C.P. Mitcheì ì, and B.A. Saxton of the Freshwater Fisheries Centre,

Rotorua. The advice and help of E. Koopu of Maraenui and B. Tawhai of

Te Kaha on Maori aspects of the kahawa j f i shery 'is gratef u'l 'ly

acknowledged. Thanks are due also to C.P. Mitchell and G.D. James forcommentjng on the manuscrìpt, and to Mrs E. Roe for typìng the orjginalmanuscri pt.

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Environmental Report NoJ' 14 P'


lssN 01 13-2504

New TealandFreshwater Fisheries Report

No. 103The kahawa¡ f¡shery

at the Motu River mouth.

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MAFFishNew Zealand freshwater fisheries report no. 103 (1988)

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