Fish and Crayfish Completed)

8/3/2019 Fish and Crayfish Completed)

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Fishandcrayfishcommunitiesof

theBlackwood

River:

migrations,

ecology,andinfluenceofsurface

andgroundwater


2/185

Fishandcrayfishcommunitiesofthe

BlackwoodRiver:

migrations,

ecology,

and

influenceofsurfaceandgroundwater

Preparedfor

SouthWestCatchmentsCouncil

&DepartmentofWater

December,2006

Preparedby

Section1

MigrationpatternsofthefishandcrayfishfaunaoftheBlackwoodRiverSJBeatty,FJMcAleer&DLMorgan

CentreforFish&FisheriesResearch

MurdochUniversity

SouthStMurdoch

WesternAustraliaEmail:[email protected]

Section2

CrayfishburrowingactivityintheregionoftheYarragadeeDischarge

Zone,BlackwoodRiver

AKoenders

&

PHJ

Horwitz

CentreforEcosystemManagement

EdithCowanUniversity

100JoondalupDrive,Joondalup

WesternAustralia


3/185

Summary

Section1 Migration patterns of the fish and crayfish

faunaoftheBlackwoodRiver

SouthwesternAustraliahasahighlyendemicfreshwateraquaticfauna,with

80%ofthefishesand100%ofthecrayfishesfoundnowhereelse. Eachofthe

endemic fishes is found within the Blackwood River catchment, with two

beingrestrictedtothefloodplainsoftheScottRiver;amajortributaryofthe

Blackwood. Salinisation of the catchment has compromised the natural

rangesofmanyofthefishes,withmanyofthenonhalotolerantspeciesnow

restrictedtoforestedtributarieswithinthelowercatchmentandinthesection

ofthemainchannelwheresalinity isreducedasaconsequenceofdischarge

fromtheYarragadeeandLeedervilleaquifers.

Prior to thisstudy,onlysnapshot fishsurveysaround themajorregionsof

LeedervilleandYarragadeegroundwaterdischargeintotheBlackwoodRiver

existed allowing only a limited understanding of the ecology of the fish

communities and their relationship with key environmental variables;

particularly surface and groundwater hydrology. This knowledge is

important in the light of potential future increased groundwater extraction

andclimatechange. Tofurthertheunderstandingofthefishcommunitiesof

thisregion,Section1ofthisstudyexaminedthetemporalmigrationpatterns

of fish and freshwater crayfish in this zone of the Blackwood catchment.

Specifically, upstream and downstream migration patterns of fishes in the

BlackwoodRiverand itstributarieswereexaminedandrelated toanumber

ofkeyenvironmentalvariables,suchassurfaceandgroundwaterdischarge.Predictions of the effects on faunaby projected changes in environmental

variables,forexample,duetoaquiferdrawdown(e.g.reduceddischargeand

increasedsalinity)wereexamined.


4/185

Substantial differences in fish densities and migration patterns existed

between and within the main channel and major tributaries. The main

channel was dominatedby estuarine and salttolerant species at all sites.

However, main channel sites receiving most groundwater discharge (i.e.

receiving both Leederville and Yarragadee Aquifer discharge) had much

greaterabundancesofnonsalt tolerant freshwaternativespecies than those

sitesupstreamoftheYarragadeedischarge. Thissuggeststhatalthoughthe

fish community in the main channel may have changed to primarily salt

tolerantspeciesinresponsetoincreasingsaltlevels,freshgroundwaterinputinsummer(whenmanytributariesceasetoflowordrycompletely),maybe

enablingthosespeciestocontinuetosurviveinthemainchannel.

ThestudyalsorecordedaconsiderableupstreammigrationoftheFreshwater

Cobbler at all main channel sites in spring and summer; a period that

coincided with their spawning. It was found that upstream Freshwater

Cobblermigrations inmain channelsiteswerehighlycorrelated tosummer

discharge. Thisspeciesisconsideredtobeidealforlongtermmonitoringof

riverconnectivity.

The Marron population was assessed in the main channel and a slightly

higherrelativeabundance(althoughnotstatisticallysignificant)wasrecorded

withinsitesreceivingmostgroundwaterdischarge(i.e.bothLeedervilleandYarragadee Aquifer discharge) than those upstream. Marron catches have

recentlybeen found tobepositivelycorrelatedwith river flowand thishas

implications for the recreational fishery within the Blackwood River under

reducedflowscenarios.

Considerabledifferences in the timingandstrengthsoffishmigrationswere

recordedbetweentributariesfortheWesternMinnow,NightfishandWestern

Pygmy Perch, that utilised all four tributaries to varying degrees. It was

foundthatthetributariesactasthemajorspawninghabitatsforthesespecies

and the section of the main channel that receives the most groundwater

discharge acts as a refuge to the summer contraction or drying of most of


5/185

MilyeannupBrook isoneofonly two (alongwithPoisongully)perennially

flowingtributariesinthisregionoftheBlackwoodandaredirectlyrelianton

YarragadeeAquiferdischarge. Itwasapparent that thissystem isofcritical

conservation importance as it houses the only population of the Balstons

Pygmy Perch in the Blackwood River catchment (listed asVulnerable under

the EPBC Act 1999). This study found a clear upstream and downstream

spawningmigrationofBalstonsPygmyPerchinthissystemandfoundonly

limitedupstreammovementfromthemainchannelsuggestingitisacrucial

refuge to Balstons Pygmy Perch in the Blackwood River catchment. Bymapping fishdistributionsalong its length insummer, thestudyalso found

thatBalstonsPygmyPerchonlyutilisedthelower~1300mofthe~2500mbase

flowstreamlengthsuggestingthatonly~52%containedsuitablehabitat(e.g.

adequatedepth)foroccupation. Theminimumpopulationofthisspecies in

thissystemwas found tobe~38042 fishbasedon theirdensity. This low

populationminimummakes thisspeciesparticularlyvulnerable topotential

habitat decline; particularly if main channel summer water quality decline

exceedsthisspeciesenvironmentaltolerance.

A number of key knowledge gaps pertaining to the ecology of the fish

communitiesare identified. Majorknowledgegaps includedetermining the

degreeofinterannualvariationingroundwaterrelianceofthesecommunities,

salinity tolerancesof thesespecies,and identifyingcriticalrifflezones in theBlackwoodRiverthatareimportantinmaintainingriverconnectivity.


6/185

Section2 Crayfishburrowingactivityintheregionofthe

YarragadeeDischarge

Zone,

Blackwood

River

Astudyoftheburrowingactivityoffreshwatercrayfish intheregionof the

Yarragadee Discharge Zone was conducted over the period of one year,

starting September 2005. The aims of the study were to determine seasonal

effects onburrowing activity for freshwater crayfish species in response to

groundwater and surface water changes, and to relate these to emergentcrayfish. In addition, a pilot study of the chemical characteristics of surface

andgroundwaterintheareawasundertakentodetermineifdischargefrom

the Yarragadee wasdetectable and if it was a migratory cue for freshwater

crayfish.

TransectsweresetupincreeksreceivinginputfromtheYarragadee(LaymanBrook, Poison Gully and Milyeannup Brook), as well as in control sites

upstream(McAteeBrook)anddownstream(RosaBrook).Burrowingdensity

andactivityweremonitoredfromOctober2005toSeptember2006,aswellas

basic surface water and groundwater physicochemistry. In addition,

observationsweremadeofemergentcrayfishduringthedayandatnight.

The study area appears tobe typicalburrowing habitat for southwesternAustralianfreshwatercrayfish.Fourspeciesoffreshwatercrayfishwerebeen

identified:Marron(Cheraxcainii),Gilgie(C.quinquecarinatus),RestrictedGilgie

(C.crassimanus)andKoonac(C.preissii).Burrowsandburrowingactivitywere

highlyseasonalandprovidebaselinedataonfreshwatercrayfishresponsesto

declinesinsurfaceandgroundwater.

The very dry autumn and early winter experienced in 2006 resulted in a

slower than usual recovery of water levels (i.e. water levels experienced in

September 2005 were much higher than those found in the corresponding

monthin2006).Whilesomemethodologicalproblemswereencountered(i.e.


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- Koonacsaremorelikelytooccurinhabitatswithadeeperreachtothe

watertable;

- the Restricted Gilgie may have resident populations in the twopermanent streams receiving Yarragadee discharge throughout the

year.

Future monitoring of transects or other sites can test the following

hypotheses:

A.

If

groundwater

decline

in

Milyeannup

Brook

and

Poison

Gully

is

extending

beyond historical ranges then the burrowing activity of freshwater crayfish will

produce soil from a lower stratigraphic soil layer than previously observed.

B. Ifgroundwater decline is extending beyond historical ranges, thenperiods of

burrowing activitywill occur earlier in spring, andburrowswill open later in the

autumnorwinter.

Water samples were also collected in November/December 2005 before

surface waters had receded, where the influence of groundwater discharge

wasrelativelyminimal,andinMarch2006whengroundwaterdischargewas

a more significant contributor to surface waters. The elemental suites of

samples from transect surface waters, and other selected sites were

determined.Thepilotstudyofelementalwaterchemistrydemonstrated the

potential for characterising the Yarragadee discharge. In addition, highS:(Ca+Mg) ratios in Poison Gully and Milyeannup Brook indicate poor

buffering and, if confirmed, may show potential for acidification should

sedimentsbecomeexposedduetodroughtand/orgroundwaterdecline.


8/185

Contents

Summary...............................................................................................................3

Contents................................................................................................................8

Section1Migrationpatternsoffishandcrayfishfauna

ofthe

Blackwood

River

... 10

Background.............................................................................................................11FishandfreshwatercrayfishesoftheBlackwoodRiver...11

Importanceofgroundwatertoaquaticfauna..12

GroundwatercontributionstoBlackwoodRiverflow.... 13

MilyeannupBrookandPoisonGully..... 14

Aimsofthestudy... 14

Methodology...........................................................................................................15Studysiteselection...15

Waterqualitymonitoring...17

Fishandcrayfishmonitoringprotocols....... 20

Resultsanddiscussion.........................................................................................25

Water

quality

in

the

main

channel

and

tributaries....25Speciescapturesummary.....34

FreshwaterCobbler..... 36

WesternMinnow.....45

MudMinnow......56

BalstonsPygmyPerch....59

WesternPygmyPerch.....63

Nightfish......71

Southwestern

Goby.....79

SwanRiverGoby.....84

WesternHardyhead.....88

PouchedLamprey.....94

EasternMosquitofish..... 97

Goldfish....... 100


9/185

Section 2 Crayfish burrowing activity in the region of

Yarragadee

Discharge

Zone,

Blackwood

River...140

Aimsandobjectives........................................................................................141

Crayfishburrowing...........................................................................................142Methods....................................................................................................................142Transectestablishmentanddesign....142

Watercharacteristics....142

Crayfishburrowmonitoring...144

Results.......................................................................................................................146Transectdata.... 146

BlackwoodRiverStPatricksElbow.....146

LaymanBrookLaymanRoad........147

LaymanBrooktributaryLaymanRoad....148

LaymanBrookCrouchRd........149

MilyeannupBrook

Helyar

Rd........151

MilyeannupBrookMilyeannupRd..152

McAteeBrookCrouchRd.........153

McAteeBrooktributaryCrouchRd..154

PoisonGullyBlackwoodRd..156

RosaBrookCrouchRd..157

RosaBrooktributaryCrouchRd...159

RosaBrookheadwaterMowenRd....160

RosaBrook

gully

Mowen

Rd....161

Transectcomparisons......162

Burrowingactivityandmigratorybehaviourofspecies...164

Discussionandrecommendations..... 166

Waterchemistry.................................................................................................168Introduction...........168

Methods.................. 168Results............. 169

Discussionandrecommendations......171

Appendices.........174


10/185

Section 1

Migrationpatterns

of

the

fish

and

crayfish

fauna

of

theBlackwoodRiver

SJBeatty,FJMcAleer&DLMorgan


11/185

BACKGROUND

FishandfreshwatercrayfishesoftheBlackwoodRiver

ThefishfaunaoftheBlackwoodRivercatchmentwasdocumentedinMorgan

etal.(1998,2003)andthereareadditionalrecordsofthefishesintheWestern

Australian Museum collections and in the unpublished literature. These

includeabaselinestudyonfishesintheYarragadeeAquiferDischargeZone

(hereafternamedYADZ)byMorgan&Beatty (2005)andbyCENRM (2005)andastudyonRosaBrook(Morganetal.2004). Distributionalinformationon

freshwater crayfish in the region is detailed in Morrissy (1978), Austin &

Knott(1996),Horwitz&Adams(2000),Nickoll&Horwitz(2000),Morganet

al.(2004a)andMorgan&Beatty(2005).

Ofnoteisthefactthatalleightspeciesoffreshwaterteleostthatareendemicto southwestern Western Australia are found within the Blackwood River

catchment(Morganetal.1998,2003). Salinisationthroughoutbothmostofthe

upper catchment and the main channel has led to adecline in the range of

manyofthesaltintolerantfishesandmuchoftheuppercatchmentandmain

channel is dominatedby salttolerant species (Morgan et al. 2003). Thus,

salinisationofthecatchmenthasseenmanyofthespeciesthatarenottolerant

tohighersalinitylevelsbecomerestrictedtotheforestedsectionsoftheriverthat receive discharge from sources such as the Leederville Aquifer and

YarragadeeAquifer(Morganetal.2003,Morgan&Beatty2005). Thereislittle

historical information on the fish and freshwater crayfish fauna of the

receivingenvironmentsurroundingtheYarragadeedischargearea,however,

CENRM (2005)recordedamaximumof fournativeandone introducedfish

speciesfrom19mainchannelsitesandamaximumofthreenativefishspeciesfrom13tributarysitesfromsamplingduringJuly2004. Incontrast,Morgan

&Beatty (2005) foundninenativeand two introduced fish species from six

mainchannelsitessampledandninenativeandtwo introducedfishspecies

from 21 tributary sites in this area of the catchment. Differences in the


12/185

receivesummerinputfromtheYarragadee,11speciesoffishandfourspecies

crayfishwere captured compared to four species of fishand two species of

crayfishupstreamofthedischargezone. Furthermore,thefourspeciesoffishin the main channel in the upper riverine part of the study area were all

halotolerant,whereasmostoftheadditionalspeciespresentinthesitesinthe

lowersectionoftheriverarethoughttotolerateonlyrelativelylowsalinities.

Anumberofspeciesfoundinthemainchannelaregenerallyabsentfromthe

tributary sites sampled and vice versa. For example, Freshwater Cobbler(Tandanus bostocki), Western Hardyhead (Leptatherina wallacei), Swan River

Goby(Pseudogobiusolorum)andSouthwesternGoby(Afurcogobiussuppositus)

wereallpredominantlycaptured in themainchannel,whileMudMinnows

(Galaxiella munda) and Balstons Pygmy Perch (Nannatherina balstoni) were

restricted to tributariesand, in thecaseof the latter species, toessentiallya

singletributary.

Of the fish species known from the Blackwood River catchment: four are

listedon theAustralianSociety forFishBiologysListofThreatenedFishes,

whileone,BalstonsPygmyPerchhasrecently(2006)beenlistedasVulnerable

undertheEPBCAct1999,and,alongwiththeMudMinnow isalso listedas

Schedule1byCALMundertheWildlifeConservationAct1950. Theseendemic

fisheshaveundergonemassivereductionsintheiroverallrangeoverthelast100years (Morganetal.1998), largelyasaresultofmodificationofhabitats,

with salinisation of the major catchments a key threatening process (see

Morganetal.2003).

The11speciesof freshwatercrayfishesofWesternAustraliaareallendemic

to the southwest region. Six of these belong to the genus Cherax, and

although this

is the most widely distributed freshwater crayfish genus in

Australia, thenativeWesternAustralianCheraxspecieshavebeenshown to

be monophyletic probably due to the long period of separation of south

western Australia to the rest of the continent (Crandall et al. 1999). The

remaining five native species of freshwater crayfish in Western Australia


13/185

degree of dependency on groundwater (Boulton & Hancock 2006).

Groundwaterdependentecosystemsare complex,often support a relatively

diverse fauna and may provide refugia for relictual species, however theyvary in their degree of dependency on groundwater to maintain their

compositionandfunction(Hattons&Evans1998,Poweretal.1999,Murrayet

al.2003,Humphreys2006). Localisedareasofgroundwaterwaterdischarge

into streams creates a unique environment known as the hyporheic zone.

Characteristics of this region are important in maintaining populations of

aquatic species, including fish. For example, the hyporheic zone oftenprovides a thermal refuge for aquatic speciesbybuffering against extreme

upper and lower lethal temperatures (Power et al. 1999, Hayashi &

Rosenberry 2002). The hyporheic zone influences water quality by

maintaining flows independent of surface runoff, supplying dissolved

oxygen, maintaining stream productivity, and providing habitat and

maintainingmigratoryroutes. Thereareanumberofspecificexamplesthat

document the importanceofgroundwater toparticular species inparticularsystems, however, Sear et al. (1999) considered that the nature of the

importance of groundwater is difficult to determine at a regional scale,but

shouldbeassessedatalocalorcatchmentlevel.

Amajoraimofthestudywastodeterminetherelationshipbetweenfishand

freshwater crayfish communities and environmental variables within theBlackwoodRiver;includingdegreeofgroundwaterdependency.

GroundwatercontributionstoBlackwoodRiverflow

The Yarragadee Aquifer groundwater currently discharges into the

Blackwood River in the reachjust downstream of Laymans Brook tojust

upstream of Milyeannup Brook (Figure 1). Although the Yarragadeegroundwaterdischarge contributesonly~1%of the940GLyr1of theannual

Blackwood River discharge during the dry months, groundwater from the

Yarragadee and Leederville Aquifers contribute tobetween 30100% of the

dischargedependingontheamountofsummerrainfall(Strategen2006).This


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the freshwater native fish moving into the main channel in the Yarragadee

Aquifer discharge zone. A previous study by Morgan & Beatty (2005)

revealedthatmostofthesespecieswereabletoexistinthisdiluteddischargezone in the main channel during summeryet werenot found in significant

numbersupstreamofthatzone.

MilyeannupBrookandPoisonGully

Asmentioned,MilyeannupBrookandPoisonGullyaretheonlypermanently

flowingstreamsinthisregionoftheBlackwoodRiver. Theirbaseflows(dryperiod)aremaintainedbydirectdischargefromtheYarragadeeAquifertoa

distanceof~2500and3500mfromtheirconfluencewiththemainchannelof

theBlackwoodRiverduring2006. MilyeannupBrookhasarelativelydistinct

channel form whereas Poison Gully is more diffuse with a lower gradient

creatingalmostawetlandappearance insomesections. Due to thereliance

ongroundwaterforpermanency,watertablereduction inthe lowersectionsof both Milyeannup Brook and Poison Gully would reduce baseflow

dischargeandalsostreamlength(Strategen2006).

Aimsofthestudy:Theoverallaimofthestudywastorelatepatternsoffishandcrayfish

migrationstoprevailingenvironmentalvariablesintheBlackwoodRiver.

Specificaims

were

to:

Comparethepopulationdemographicsandmigrationsofthefish

andfreshwatercrayfishfaunawithinareasoftheBlackwoodRiver

main channel that receivemajor groundwater discharge to those

upstreamsitesthatdonot.

Describethepopulationdemographicsandmigrationsof thefish

and freshwatercrayfish faunaassociatedwithin the tributariesofthe Blackwood River within the Yarragadee Aquifer discharge

zone (i.e. Milyeannup Brook, Poison Gully and Layman Brook)

andcompare these toadjacent tributaries thatarenot fedby this

aquifer(i.e.RosaBrookandMcAteeBrook).


15/185

METHODOLOGY

Studysiteselection

BlackwoodRivermainchannel

Site selection for determining the temporal changes in population

demographicsandmigrationsofthefishandcrayfishfaunaintheBlackwood

Rivermainchannelwasbasedontheirdifferingproximitiestothemajorzone

ofgroundwaterdischarge. Forexample,thefishfaunafoundwithintwositesintheBlackwoodRivermainchannelthatissubjectedtothemajordischarge

of ground water (from the Yarragadee Aquifer) was compared to two sites

upstreamofthisdischarge.

The twositeswithin themainchannel that receivegroundwater inputwere

immediately downstream of the mouth of Milyeannup Brook (34.0909

o

S115.5661oE) and just upstream of the mouth Rosa Brook (34.1081oS,

115.4505oE). The two upstream sites include Jalbarragup Road crossing

(34.0421oS,115.6025oE)andQuigup(33.9736oS,115.7008oE)(seeFigure1).

Sampling was conducted in October, November and December 2005 and

February, March,June, August and September 2006. See page 20 for the

biologicalsamplingregime.

BlackwoodRivertributaries

MilyeannupBrookandPoisonGullyaredirectlymaintained indrymonths

by groundwater discharge. Layman Brook receives groundwater discharge

during winter and springbut not summer; when it ceases to flow. The

temporalchangesinthepopulationdemographicsandmigrationsofthefishandcrayfishfaunawithinthesetributarieswerecomparedwithtwoadjacent

tributariesthatflowseasonally,i.e.RosaBrookandMcAteeBrook;withinthe

LeedervilleAquiferdischargezone.


16/185

Rosa Brook Layman Bk

Milyeannup PoolDenny Rd

Poison Gully

Milyeannup Brook

Jalbarragup

McAtee Bk

Quigup

Main channel sites

Tributary fyke net sites

Seine/electrofishing tributary sites


17/185

Waterqualitymonitoring

In order to characterise the climatic regime during the sampling period,relative to thehistoricalclimateof the region, rainfalland temperaturedata

were obtained for the Australian Bureau of Meteorology for Bridgetown; a

locationforwhichlongtermdatawereavailable. Thisisimportantasithas

implications in terms of the appropriateness of the biological data as a

baselineand forunderstanding interannualvariations in futuremonitoring

programs.

Inordertogainamorepreciseunderstandingoftemperatureregimesofthe

various tributaries sampled in this study, temperature data loggers

(TinytagTM)wereplacedinsituintomigrationsamplingsitesinthetributaries

(Figure 1) and programmed to log temperature every three hours.

Temperature loggers were also put in situ at the Blackwood River main

channel sites. Data from the loggers were downloaded and temperatureregimesofthevariousaquaticsystemsweregraphicallycompared.

Oneach samplingoccasionat each site, the temperature (in addition to the

temperature data loggers), conductivity, pH, and dissolved oxygen were

obtainedfromthemiddleofthewatercolumnatthreelocationsateachsites

andamean(1SE)determined.

MonthlydischargeestimatesineachtributarysiteweretakenbyDepartment

ofWater(Bunburybranch)staffattheapproximatetimesthatsamplingtook

place for fishmigrations. Main channel dischargeswereobtained from the

DepartmentofWatergaugingstationsatNannup(approximatingtheQuigup

sampling site), Darradup (upstream of the Yarragadee discharge,

approximatingJalbarragupsamplingsite),Gingilup(receivingthemajorityoftheYarragadeedischarge in themainchannel,approximating theDennyRd

samplingsite). ThemonthlydischargefortheMilyeannupPoolsamplingsite

(at the uppermost point of the Yarragadee discharge) was estimated as the

average of the monthly Darradup and Gingilup discharges (see Figure 2)


18/185

Lower Blackwood River

HutPool

Sues

Bridge

Gingilup

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

40 50 60 70 80 90 100 110 120Dist f rom Molloy Is. (km)

Flow(m3/s)

Flow (Mar2003)Flow (Mar2004)Flow (Feb2005)Flow (Mar2006)"LimitsBaseflowLBF (Mar2006)LBF (Mar2003)LBF (Mar2004)LBF (Feb2005)

Layman Brook

Darradup

Poison Confl

Milyeannup Confl

609-1362

Figure2 Snapshotofdischargewithin the studyarea inMarch2003,2004,2005and

2006. N.B.verticaldotted linesapproximateYarragadeeAquifer discharge

boundaries. FigurebyDepartmentofWater,Bunbury.

Determiningkey

environmental

variables

for

migration

strengths

data

analysis

The relationships between the strength of native fish migrations in the

tributaries and the main channel and key environmental parameters were

examinedviaregressionanalyses. Fortributaries,thenativespeciesincluded

in analyses were those where adequate migration data were recorded (i.e.utilised themostnumberof tributaries)and included theWesternMinnow,

Western Pygmy Perch, and Nightfish. For the main channel, the analysis

focused on the Freshwater Cobbler, which was captured in the greatest

numbersatallsites.


19/185

this major flow and/or breeding period explained the most variation in

upstreamanddownstreammigrationsofthosespecies.

WithinthemainchanneloftheBlackwoodRiver,theassociationbetweenthe

strength of upstream and downstream Freshwater Cobbler movements and

the above key environmental variables (with discharge data obtained from

the Department of Water gauging stations at Nannup, Darradup and

Gingilup)weresimilarlyexamined. Firstly,allsamplingoccasionsatallsites

were included in stepwise regression analysis to determine which of theenvironmentalvariablesexplained thevariation inupstreamordownstream

Freshwater Cobbler movements in the Blackwood River. Secondly, overall

meanupstreamanddownstreamFreshwaterCobblermovements ineachof

the four main channel sites, pooled for the major migration period (i.e.

betweenNovemberandJuly),werecorrelatedwiththeaboveenvironmental

variables during that period to determine which, if any, accounted for the

observeddifferencesinmigrationstrengthsbetweenthosesites.

For the above analyses, ShapiroWilk statistical tests for normality were

undertaken for each variable and all data were subsequently log10

transformed prior to analysis. Bivariate correlations between each

environmental variable were calculated (Pearsons correlation coefficient)

prior to each stepwise regression analysis to initially examine relationshipsbetween environmental variables. Mean velocity was consistently highly

correlated with discharge and was therefore excluded from the analyses to

avoidproblemswithcolinearity.

Inthesubsequentstepwiseregressionanalyses,levelsofcolinearitybetween

independent variables were investigated via determining condition indexes

and eigenvalues. The more conservative, adjusted coefficients of

determination(r2)wereexaminedineachmodelastheadjustedvaluesclosely

reflect thegoodnessof fitof themodel. The significanceof the modelsare

alsopresented(pvalues)(SPSS,2005).


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Fishandcrayfishmonitoringprotocols

A number of techniques were employed to examine the fish and crayfish

faunaofthemainchannelandtributarysitesintheBlackwoodRiver(Figure

3). Eachmethodisoutlinedbelow,i.e.theuseoffykenets(11.2minwidth,

includingtwo5mwingsanda1.2mwidemouthfishingtoadepthof0.8m,

5mlongpocketwithtwofunnelsallcomprisedof2mmwovenmesh);seine

nets(5,10and15mnetscomprisedof2mmwovenmesh;anda26mseine

netconsistingoftwo9mwingsof6mmwovenmeshandan8mbuntof3mmmesh);240and12velectrofishers;andcrayfishtraps.

BlackwoodRivermainchannel

Speciesmigrations

At the fourmainchannelsites (seeFigures1and3), fykenetswereused to

determine temporal trends inspeciesmigrations. Fykenetswereset facingupstream, to determine downstream movements of fish, and facing

downstream, todetermineupstreammovementsof fish. Each fykenetwas

setforaperiodof24hwiththreereplicatestakenoneachsamplingoccasion.

Each fish and freshwater crayfish captured was identified, a subsample

measured (total length (TL) for fish and orbital carapace length (OCL) for

crayfish) to the nearest 1 mm and where possible sexed and released. Asubsampleofmostspecieswasretainedforanalysesofbiologicalindicessuch

as gonadal development and aging, some of which are provided in this

report,butmostofwhicharetobeinvestigatedfurther.

Duetothehighvolumeofwaterandlargewidthofthemainchannelitwas

rarely possible to completely block the main channel sites and thereforecapture all fish moving upstream or downstream past a point at the site.

Therefore, themeannumberofeachspeciescapturedoneachoccasionwas

adjusted to account for total number of each species migrating through a

sectionof the river. Forexample, ifour fykenetsblocked90%of themain


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Figure3 Fykenetsset in (A) themostupperBlackwoodRivermainchannelsite, i.e.

Quigup, (BC)Jalbarragup, (DE)upstreamofRosaBrook (DennyRd),and(F)MilyeannupPooldownstreamofMilyeannupBrookmouth.

Speciesabundances

A

C

B

D

E

F


22/185

BlackwoodRivertributaries

On each sampling occasion (if the system was flowing), fyke nets were setover three days and nights in Milyeannup Brook (2 sites), Layman Brook,

RosaBrookandMcAteeBrook(Figure4). Ateachsite,onenetwassetfacing

upstream,tocapture fish thatweremovingdownstream,whileanotherwas

set facing downstream (to capture fish moving upstream) and each was

checkedevery24h (Figure4). Aswith themain channel site captures, the

percentcoverageofeachsetwasdeterminedandthecatcheslateradjustedto100%ofthestreamwidth.

A

C

B

F

D

E


23/185

Theshallow,diffusenatureofPoisonGullyprohibitedeffectivesamplingfor

fish migration; therefore, a seasonal quantitative analysis of the fish and

freshwater crayfish was undertaken using abackpack electrofisher. Threereplicate density estimates were taken with up to 90 m2 sampled on each

occasion. In addition, electrofishing was employed in October 2005 in

McAtee, Rosa and Layman Brooks and again in December 2005 in McAtee

Brooktoexaminespeciesdemographics. Regardlessofcapturemethod,fish

species were identified, with a large subsample measured for total length

(mm TL) for fish and orbital carapace length (mm OCL) for freshwatercrayfishandbeforebeingreleased. Thosenotmeasuredwere identifiedand

counted to determine total numbers. A small subsample of native species

wasretainedforbiologicalinvestigationintothegonadaldevelopment(upto

~30permonth)andforfuturegeneticanalysis.

Freshwatercrayfishwereidentified,measuredtothenearestmmOCL,sexed

and released. A small number were retained for determination of size at

sexualmaturity.

Marronpopulationanalysis

Samplingregime

In order to compare the relative abundances of Marron at sites within the

mainchanneloftheBlackwoodRiver,samplingforMarronoccurredatatotalof six sites in the Blackwood River on seven sampling occasions;

correspondingwiththefishmigrationsampling. Inadditiontothefoursites

sampled for fish migrations, an additional two were selected (near the

confluence of Red Gully, upstream of the YADZ, and near the entrance of

Laymans Brook, at the most downstream point of the YADZ) in order to

sample a greater range of representative habitats within and outside of the

majorzoneofgroundwaterdischarge toavoidpotentialbias resulting from

accessibilitybyrecreationalfishers(Figure2).

Oneachsamplingoccasion,up to13boxstylecrayfish trapsweredeployed

i ht d i t l 15 t T b it d ith lt


24/185

trappernight. ThestatisticalsignificanceofCPUEwastestedusinggeneral

linearmodels (ANOVA)withLevenes testofhomogeneityofvariance first

beingconductedanddatabeinglogtransformedwhennecessary.

In order to compare population structures of Marron in the sites receiving

YADZ (i.e. Milyeannup Pool; near the Laymans Brook confluence, and at

DennyRoad;near theRosaBrookconfluence) to thosesitesupstreamof the

zone (i.e.near the confluenceofRedGully,JalbarragupRoad crossing,and

Quigup), lengthfrequency distributions over the sampling months wereproducedforeachof thetwozones. ThemajorspawningperiodofMarron

was determinedby examination of the temporal pattern in proportions of

femaleovarianstages(seeBeattyetal.2003,2005).

The OCL at which 50 (L50) and 95% (L95) of female Marron mature in the

BlackwoodRiverwasdeterminedbyundertakinglogisticregressionanalysis

ofthepercentagecontributionsmadetoeachlengthclassbyindividualsthat

containeddeveloping/maturegonads(stagesIIIVII). Datawererandomly

resampled and reanalysed to create 500 sets ofbootstrap estimates. The

logisticequationis:

POCL=1/[1+eln19(OCL OCL50)/OCL95 OCL50)]

wherePOCLis the proportion of Marron with mature gonads (seebelow) at

lengthintervalOCL. OnlythoseindividualscapturedinJulyandAugust(i.e.

immediatelyprior toand throughout thebreedingperiod,seeResults)were

usedintheanalysis(forfullmethodologyseeBeattyetal.2004).

FreshwaterCobblerpopulationanalysis

Inorder to furtherexaminepatterns inmigrationsofFreshwaterCobbler,a

totalof437weretaggedusingindividuallynumberedtbartagsateachmain

channelsiteoverthestudyperiod(seeTable3). Thetotallengthofeachfish

tagged and recaptured was measured to aid in the future validation of

growthandmovementsof this species. Furthermore, ineachmonthof the

i i ti i d (l t i l t Fi 17) th


25/185

RESULTSandDISCUSSION

Waterqualityinthemainchannelandtributaries

Climateduringthestudyperiod

The analysis of the seasonal pattern in climate for the region revealed an

atypical pattern in air temperature and rainfall for the sampling year(s)

comparedwithhistoricaldata(Figures5and6). Specifically,thefirsthalfof

thesamplingperiod(i.e.spring2005andsummer20052006)wasunusuallycoolcomparedwiththelongtermaverage(Figure5). Furthermore,therewas

an unusually late start to the wet season in 2006 (i.e.July compared with

April/May historically) (Figure 6). Therefore, the seasonal patterns in fish

movementsdescribed in this reportmaydiffer to thatofa typicalyearand

this interannual variation requires quantification by further seasonal

sampling. For example, the relatively late onset of winter rains in 2006probablyresultedindelayedseasonalsurfaceflowsinRosaBrook,Laymans

BrookandMcAteeBrookthatarenotmaintainedbygroundwaterdischarge

comparedtoMilyeannupBrookandPoisonGully,whichhaveperennialflow

duetoYarragadeeAquiferdischarge.

Temperature

(C)

20

22

24

26

28

30

32Study period

Long term (1887-2004)


26/185

Month

Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug Sep

Rainfa

ll(mm)

0

20

40

60

80

100

120

140

160

180

Monthly rainfall during study

Long term monthly rainfall (1887-2004)

2005 2006

Figure6 Monthly rainfall in Bridgetown during the study period compared with the

longtermaverage(18872004,source:AustralianBureauofMeteorology). N.B

theaboveaveragerainfallfromOctober2005January2006andconsiderably

laterstarttothewinterrainfall(i.e.July2006)andverydryautumncompared

withthelongtermaverage.

Aquaticenvironmentalvariables

From the temperature data loggers (from which weekly means were

determined to smooth the data), it was apparent that patterns of water

temperatures in the Blackwood River and its tributaries corresponded with

variationsinairtemperature(Figure7). However,theleastseasonalvariation

(i.e. remained coolest in summer and warmest in winter), and thus more

stable temperatures, were recorded in Milyeannup Brook. As noted, this

system receives direct discharge from the Yarragadee Aquifer which

maintainsperennial flow for the lower~2500mofstream length (seesection


27/185

Month

Nov Jan Mar May Jul Sep

Watertem

perature(C)

5

10

15

20

25

30

35

Milyeannup Brook - Brockman Hwy

Rosa Brook - Denny Rd

McAtee Brook - Longbottom Rd

Laymans Brook - Denny Rd

Blackwood River- Milyeannup Pool

Milyeannup Brook - Blackwood Rd

Bridgetown mean maximum air temperature

Blackwood River - Denny Rd

Figure7 Mean weekly temperatures (1 SE) at the sampling sites in the tributaries, two

main channel sites (Milyeannup Pool at the upstream point of Yarragadee

discharge and Denny Rd receiving all of the Yarragadee discharge), and themaximumairtemperatureatBridgetown. N.B.the lowerseasonalfluctuationof

the mean temperature in lowerMilyeannupBrook (maintainedbygroundwater

discharge) compared with those reliant on surface flows, and the marked

influenceofairtemperatureonwatertemperatureatthesesites.


28/185

Month

Oct Nov Dec Feb Mar Jun Aug Sep

Temperature

(C)

10

12

14

16

18

20

22

24

26 Denny Rd

Milyeannup Pool

Jalbarragup

Quigup

2005 2006

Figure8 Meantemperatures(1S.E.)atthesamplingsitesinthemainchannelofthe

BlackwoodRiveroneachsamplingoccasion.

This consistency of water quality in the two perennial tributaries was

highlighted by the relatively consistent conductivities recorded in these

systems compared with systems that cease flowing. Those latter systemsincrease in conductivity during summer as a result of evapoconcentration

(Figure 9a). The increased cumulative discharge of groundwater into the

mainchannelduringsummerattheMilyeannupPoolandDennyRdresults

in those sites having reduced conductivities (e.g. ~2030 S/cm at Denny Rd in


29/185

A

Month


Conductivity(S/cm)

0

200

400

600

800

1000

1200

Rosa Brook

Laymans Brook

McAtee BrookMilyeannup Brook - upstream

Milyeannup Brook - downstream

St Johns Brook

Poison Gully

2005 2006

B

Conductiv

ity(S/cm)

2000

3000

4000

5000

6000

7000

8000

Denny Rd

Milyeannup Pool

JalbaragupQuigup


30/185

Month


pH

3.5

4.0

4.5

5.0

5.5

6.0

6.5

7.0

7.5

Rosa Brook

Laymans Brook

McAtee Brook

Milyeannup Brook - upstream


St John

Poison Gully

2005 2006

Figure10 MeanpH(1S.E.)atthesamplingsitesinthetributaries. N.B.theincreased

acidityinRosaBrookduringthedryperiodinMarchandJune2006.

pH7.0

7.5

8.0

8.5

Denny Rd

Milyeannup Pool

Jalbaragup Rd

Quigup


31/185

Month


Dissolvedoxygen(ppm)

2

4

6

8

10

12

14

16

18

Rosa Brook

Laymans Brook

McAtee Brook


Milyeannup Brook - downstreamSt Johns Brook

Poison Gully

2005 2006

Figure12 Meandissolvedoxygen(1S.E.)atthesamplingsitesinthetributariesofthe

BlackwoodRiveratthetimesofsampling. N.B.thelessseasonalfluctuation

in lower Milyeannup Brook compared with tributaries not receiving

YarragadeeAquifergroundwater.

solvedoxygen(pp

m)

10

12

14

16

18

20

Denny Rd

Milyeannup Pool

Jalbarragup

Quigup


32/185

Rosa Brookhad the greatestdischargeof any tributary; peaking inOctober2005, at the start of the study (Figure 14). Milyeannup Brook and Poison

Gully (although not gauged) continued to flow throughout the dry months

due togroundwaterdischarge (Figure14). Therewasageneral increase in

thedischargeratesmovingdownstream inthemainchannelsites(Figures2

and15). Asmentioned,climaticallythiswasanatypicalyearasreflectedby

relativelylowdischargeupuntilAugust2006(Figure15). OfparticularnoteisthegreaterdischargeatGingilupcomparedwithDarradupduringthedry

months (FebruaryJuly, Figure 2). This is due to Gingilup receiving the

majorityoftheYarragadeeAquiferdischargeintothemainchannelwhereas

Darradup isupstream from thedischargezone (Figure15). Thishighlights

thefactthatgroundwatercontributestobetween30and100%ofthesummer

dischargeoftheBlackwoodRiver(Strategen2006).


Meandischarge(m3/sec

)

0

1

2

3

4Rosa Brook

Laymans Brook

McAtee Brook



Poison Gully


33/185

Month

Oct05

Nov05

Dec05

Jan06

Feb06

Mar06

Apr06

May06

Jun06

Jul06

Aug06

Sep06

Oct06

Nov06

Dec06

Disch

arge(m3/sec

0

5

10

15

20

25

30

35Nannup

Darradup

GingilupHut pool

Figure15 Monthlymeandischarges(1SE)inmainchannelsitesoftheBlackwoodRiver

at the times of sampling. N.B. the greater discharge in Gingilup (receiving

downstream of groundwater discharge zones) compared with Darradup

(upstreamof theYarragadeedischargezone) fromFebruaryJune2006 (see

alsoFigure2).

Themaintenanceofrelativelylowmainchannelsalinitiesasaconsequenceof

groundwater intrusions has considerable ecological implications as during

summer, when the majority of tributaries cease flowing, many fish must

retreatintothemainchannel. Duringwinter,whenthehighestconductivities

areexperienced(Figure9),thoseindividualscanutilisethethenflowingfresh

tributariestoescapetheelevatedmainchannelsalinitiesthatmayexceedtheir

tolerance levels. Therefore, saltintolerant species, particularly Balstons

PygmyPerch,WesternPygmyPerchandNightfish,thatarecurrentlyableto

utilise thisdilutedsectionof theBlackwoodRiver,maynotbeable todoso


34/185

Speciescapturesummary

During this study, six endemic freshwater fish species, three estuarine fishspecies and three introduced fish species were captured. The anadromous

(i.e. migrates into rivers from the ocean to breed) Pouched Lamprey, a

southernhemisphereagnathan (i.e.jawless fish)wasalsocaptured,butwas

foundinonlytwotributaries. Thesixfishspeciescapturedthatareendemic

to southwestern Australia were the Freshwater Cobbler, Western Minnow,

Mud Minnow, Balstons Pygmy Perch, Western Pygmy Perch, and the

Nightfish. The estuarine species captured were the Western Hardyhead,

SouthwesternGobyandtheSwanRiverGoby. The three introduced fishes

capturedweretheEasternMosquitofish,GoldfishandRainbowTrout.

Four species of endemic freshwater crayfish were captured, including the

Marron,Gilgie,RestrictedGilgieandKoonac.

Below is an account of the distribution, population demographics and

migration patterns of each species. See also Section 2 for information

regardingcrayfishburrowingactivity.


35/185

Table1 Thetotal(andadjusted)numberofeachspeciesoffishandfreshwater

crayfishcapturedinfykenetsintheBlackwoodRivermainchannelsites.

Total number (adjusted for stream width) of individuals caught in

the Blackwood main channel using Fyke nets.

MOVEMENT

SPECIES

Downstream Upstream Total # Captured

Endemic

freshwater fishesFreshwater Cobbler 526 (1539.3) 1280 (5729.5) 1806 (7268.8)

Western Minnow 22 (175) 463 (3193.3) 485 (3368.3)

Mud Minnow 0 0 0

Balstons Pygmy Perch 0 2 (40) 2 (40)

Western Pygmy Perch 14 (54) 0 14 (54)

Nightfish 11 (73) 4 (28.3) 15 (101.3)

Estuarine fishes

South-west Goby 94 (563) 26 (158.3) 120 (721.3)

Swan River Goby 6 (34.7) 4 (10) 10 (44.7)

Western Hardyhead 13 (59.7) 12 (69.7) 25 (129.3)

Introduced fishes

Eastern Mosquitofish 14 (75) 13 (45) 27 (120)

Goldfish 0 0 0

Rainbow Trout 0 0 0

Endemic crayfishes


36/185

FreshwaterCobbler

Habitatassociations

The Freshwater Cobbler is essentially restricted to the main channel of the

Blackwood River (Figure 16, Appendices 1 and 2). The few individuals

capturedinthetributariesweregenerallysmallerfishwithonlyfive,twoand

17 captured in Rosa Brook, McAtee Brook and Milyeannup Brook,respectively (Figure 17). This was expected given this relatively large

(comparedtoothernativespeciesoftheregion)fishismorecommonlyfound

inthelargerriversandreservoirsinthisregion.

Migrationpatterns

Onalmostallsamplingoccasions, thestrengthof theupstreammigrationofFreshwaterCobblerwasgreaterthan thedownstreammigration(Figure16).

The migration strength peaked in late spring and summer, with greatest

migrationstrengthbeingrecordedinthemoredownstreamsitesthatreceived

greater groundwater discharge (i.e. Denny Rd and Milyeannup Pool)

compared to the upstream sites (i.e. Jalbarragup and Quigup). Spatial

differences in migratory patterns existed within the main channel with the

peak upstream migrations in the downstream sites occurring duringFebruary, compared to March and November in Quigup andJalbarragup,

respectively(Figure16). MovementofFreshwaterCobblerwasataminimum

duringwinter.


37/185

the fact that Freshwater Cobbler movements increased during periods of

elevatedwatertemperatures(i.e.summer).

ThemeanstrengthofupstreammovementofFreshwaterCobbleratthemain

channel sitesduring the peakmovementperiod (i.e. late spring to autumn:

November toJuly samples inclusive) was highly correlated with the mean

discharge at those sites over that period (Figure 21). Regression analysis

revealed that the overall mean monthly dischargebetween November and

July at these sites explained ~96% (p=0.014) of the variationbetween main

channelsitesinFreshwaterCobblermovementintheBlackwoodRiver. That

is,thegreaterthesummerdischargeatthesesites,thegreaterthestrengthof

migration of this species. This movement is probably due to this species

accessinghabitatsforspawningandfeeding.

Of the437 taggedFreshwaterCobbler,a totalof86 (19.7%)wererecaptured

(Table3). Of these,68wererecapturedonce,12 twice, four three timesandtwowererecapturedfourtimes(Table3). Withtheexceptionofonefish,all

were caught at the initial tagcapture site. This suggests that there is a

relativelyhighdegreeofsitefidelitybythisspeciesintheBlackwoodRiver.

Although a high degree of site fidelity occurs in this system, there are

nonethelesslarge localisedupstreammigrationsbythisspeciesduringtimesoflowflowasaprecursortospawning. Asmuchofthedryperioddischarge

intheBlackwoodRiver isadirectresultofgroundwaterdischarge(30100%

in the driest two months), this species appears reliant on this groundwater

discharge to facilitate such spawning migrations. This groundwater

dischargeisthereforeimportantinprovidingadequatepassagethroughriffle

zones that would otherwise be barriers to its migration; and would be

particularimportantinyearsoflowinputofsurfaceflows.


38/185

Meannumberoffish

0

200

400

600

800

1000

1200

1400

Downstream movementUpstream movement

Meannumberoffish

0

200

400

600

800

1000

1200

1400

Denny Road

Milyeannup Pool

Me

annumberoffish

0

200

400

600

800

1000

1200

1400

Jalbarragup

1400

Freshwater Cobbler (T. bostocki)

NS NS


39/185

Meannumberoffish

0

2

4

6

8

10

Downstream movement

Upstream movement

Meannumberoffish

0

2

4

6

8

10

Rosa Brook

Layman Brook

Meannumberoffish

0

2

4

6

8

10

Milyeannup Brook

eroffish

6

8

10

McAtee Brook

Freshwater Cobbler (T. bostocki)

DRY DRY

NFNF


40/185

Mean Gonadosomatic Indices (+1SE)

Month

November December February March

Gonados

omaticindex

0

1

2

3

4

5

Female

Male

19

37

47

65

3 2211

20

Figure18 Meangonadosomatic indices(GSI) (+1SE)formaleandfemaleFreshwater

CobblerinthemainchanneloftheBlackwoodRiverbetweenlatespringand

earlyautumn.


41/185

log10 mean temperature (oC)

1.0 1.1 1.2 1.3 1.4

log10meanfrequencyof

fish

0.5

1.0

1.5

2.0

2.5

3.0

3.5log10N = 4.77*log10T- 3.86r2 = 0.54

Figure19 RelationshipbetweenthemeanstrengthoftheupstreammigrationofFreshwater

Cobbler and the mean temperature in the Blackwood River main channelthroughoutthesamplingperiod.N.B.datawerelog10transformedandmigration

numberwasstandardisedforeffort,seetextfordetails.

eanfrequencyoffis

h

1.0

1.5

2.0

2.5

log10N = 3.53*log10D- 3.22r2

= 0.37


42/185

log10 mean discharge (M3/sec)

-0.05 0.00 0.05 0.10 0.15 0.20 0.25

log1

0meanfrequencyoffish

1.8

2.0

2.2

2.4

2.6

2.8

log10N = 2.63*log10D+2.11r2

= 0.97

Figure21 Relationship between the mean strength of the upstream migration of

Freshwater Cobbler and the mean discharge in the Blackwood River main

channelbetweenNovemberandJuly.N.B.Datawerelog10transformedand

migrationnumberwasstandardisedforeffort,seetextfordetails.


43/185

43

Table2 CorrelationsbetweenoverallmeanupstreamanddownstreammovementsofFreshwaterCobberinthe

mainchannelsitesoftheBlackwoodRiverandprevailingenvironmentalvariablesduringthemigration

period(NovembertoJuly).N.B.Datawerelog10transformed,*denotescorrelationissignificantatthe

0.05level(2tailed).

Logtemperature

Logconductivity Log pH Log O2

Logdischarge

Upstreammovement

Log conductivity Pearson Correlation .358

Sig. (2-tailed) .642

Log pH Pearson Correlation .733 .414

Sig. (2-tailed) .267 .586

Log O2 Pearson Correlation -.498 -.983* -.444

Sig. (2-tailed) .502 .017 .556

Log discharge Pearson Correlation -.470 -.787 -.837 .752

Sig. (2-tailed) .530 .213 .163 .248

Upstream movement Pearson Correlation -.426 -.680 -.871 .634 .986*

Sig. (2-tailed) .574 .320 .129 .366 .014

Downstreammovement

Pearson Correlation.273 -.690 -.241 .550 .700 .687

Sig. (2-tailed) .727 .310 .759 .450 .300 .313


44/185

44

Table3 FreshwaterCobblertaggedandrecapturedinmainchannelsitesoftheBlackwoodRiver.N.B.Includes%recapturedper

siteand%totalofallrecaptureswhencomparedtototalnumbertagged.

SITE Number

Tagged

# Recaptured

(%)

# Recaptured Twice

(%)

# Recaptured 3 times

(%)

#Recaptured 4 Times

(%)

Denny Road 215 42

(19.5)

8

(3.7)

1

(0.5)

MilyeannupPool 42 7(16.7)

Jalbarragup 110 17

(15.5)

4

(3.6)

3

(2.7)

2

(1.8)

Quigup 70 2

(2.9)

TOTAL

(%)

437 68

(15.6)

12

(2.7)

4

(0.9)

2

(0.5)


45/185

WesternMinnow

Habitatassociations

TheWesternMinnowwascapturedatthemajorityofsitessampledonmost

occasions, with large numbers recorded in both the main channel sites

(Appendix 1) and in the tributaries (Appendix 2). This widespread

distribution,beingpresentinnearlyallhabitatssampled,reflectsthisspecies

tolerance to a wide range of salinities; having previouslybeen recorded insalinitiesup to~24pptor~two thirds thesalinityofseawater (Morganand

Beatty2004).

Migrationpatterns

TherewerelimitedmovementsofWesternMinnowinthetwomostupstream

main channel sites compared to the more downstream sites, i.e. Denny Rdand Milyeannup Pool (Figure 22). Within these latter sites, the upstream

movement of Western Minnow was strongest during winter and peaked in

Augustwith,onaverage,over300individualsrecordedmovingupstreamper

day. Thesefishwerelargeadultsthatwerelikelytobemovingasaprecursor

tospawning (Figures2325). Migration intoMilyeannupBrookwashigh in

Augustandtherewaslimitedmovementofadultsintotheothertributariesat

this time. Latermigration ofadults was recorded into the other tributariesfromAugusttoNovember. UpstreammigrationsofadultWesternMinnow

continued in Milyeannup Brook throughout the entire sampling period;

presumablyasaconsequenceof theperennial flowsof thesystem resulting


46/185

to December for Rosa Brook and McAtee Brook. Only limited recruitment

occurredinLaymanBrook.

TheearlierrecruitmentoffishfromMilyeannupBrookisfurtherhighlighted

bythelargersizeofthiscohortcomparedtothoseinRosaBrookinDecember

(i.e.modallength5055mmTLcomparedto2530mmTL)(Figure27). This

earlier spawning in Milyeannup Brook, presumably as a consequence of

perennialflowsallowingearlieraccesstothetributary,isfurtherhighlighted

whenconsideringthatthenewrecruitsinthisstreamhadamodal lengthof

3540mmTLduringOctober,whichis10mmgreaterthanthenewrecruitsin

RosaBrooktwomonthslater(Figure27).

Examinationof lengthfrequencyhistogramsof fish caught inmain channel

sites compared to tributary sites reveals that the vast majority of Western

Minnows thatwe captured that were less than40 mm TL wereonly found

withinthetributaries. Thisstronglysuggeststhatbreedingtakesplacewithintributariesand that thesehabitatsare thereforevitalspawningareas for this

species.

TherearesubstantialdifferencesinthepopulationdemographicsofWestern

Minnows in the main channel sites. Specifically, fish captured in the two

mostdownstreamsitesgrew toasubstantially largersize implying that the

species hadgreater longevityat thedownstream sites compared to the two

upstreamsites. Forexample,of the fish thatweregreater than100mmTL,

almostallwerefoundattheDennyRdandMilyeannupPoolsites(thatboth

receiveYarragadeeAquiferdischarge).

The upstream and downstream migration of the Western Minnow in the

varioustributarieswerebothfoundtobepositivelycorrelatedwiththemeandischarge from the tributaries during the major flow period (August to

December)(Table4). Fromtheregressionanalysis,meandischargeexplained

~92% (p=0.027)and87% (p=0.044)of thevariation in themeandownstream

d t i ti f W t Mi b t th t ib t i d i


47/185

Meannumberoffish

0

100

200

300

400

500

Downstream movement

Upstream movement

Meannumberoffish

0

100

200

300

400

500

600

700

Denny Road

Milyeannup Pool

Meannumberoffish

0

100

200

300

400

500

Jalbarragup

eroffish

300

400

500 Quigup

Western Minnow (G. occidentalis)

NS NS


48/185

0

5

10

15

20Downstream Migration

Upstream Migration

0

5

10

15

20

0

5

10

15

20

NumberofFish

0

5

10

15

20

0

5

10

15

20

0

10

20

30

40

50

60

30

40

2005October

November

December

2006February

March

June

August

n=37

n=2

n=4

n=163

n= 177

n=6

n=17

Western Minnow (Galaxias occidentalis)


49/185

0

5

10

15

20

Numberoffish

0

5

10

15

20

0

5

10

15

20

0

5

10

15

20

0

5

10

15

20

0

5

10

15

20

0

5

10

15

20

20

2005October

November

December

2006February

March

June/July

August

September

Denny Rd

0

10

20

30

40

50

60

Numberoffish

0

10

20

30

40

50

60

0

10

20

30

40

50

60

0

10

20

30

40

50

60

0

10

20

30

40

50

60

0

10

20

30

40

50

60

0

10

20

30

40

50

60

60

2005October

November

December

2006February

March

June/July

August

September

Milyeannup Pool

NS

NS


50/185

0

5

10

15

20

Numberoffish

0

5

10

15

20

0

5

10

15

20

0

5

10

15

20

0

5

10

15

20

0

5

10

15

20

0

5

10

15

20

20

2005October

November

December

2006February

March

June/July

August

September

Jalbarragup

0

5

10

15

20

Numberoffish

0

5

10

15

20

0

5

10

15

20

0

5

10

15

20

0

5

10

15

20

0

5

10

15

20

0

5

10

15

20

20

2005October

November

December

2006February

March

June/July

August

September

Quigup

NS


51/185

Meannumberoffish

0

50

100

150

200

250

Downstream movement

Upstream movement

Meannumberoffish

0

50

100

150

200

250

Rosa Brook

Layman Brook

Meannumberoffish

0

50

100

150

200

250

Milyeannup Brook

offish 200

250

McAtee Brook

Western Minnow (G. occidentalis)

DRY DRY

NFNF


52/185

0

10

20

30

40

50Downstream

Upstream

0

10

20

30

40

50

0

20

40

60

80

100

120

Rosa Brook

NumberofFish

0

10

20

30

40

50

0

10

20

30

40

50

0

10

20

30

40

50

10

20

30

40

50

0

20

40

60

80

100

120

140Downstream

Upstream

0

20

40

60

80

100

0

10

20

30

40

50

Milyeannup Brook

NumberofFish

0

10

20

30

40

50

0

10

20

30

40

50

0

20

40

60

80

100

10

20

30

40

50

2005October

November

December

2006February

March

June

August

2005October

November

December

2006February

March

June

August


NOT FLOWING

NOT FLOWING

n=16

n=53

n=310

n=17

n=46

n=339

n=306

n=117

n=241

n=162

n=34

n=13


53/185

0

10

20

30

40 Downstream

Upstream

0

10

20

30

40

0

10

20

30

40

Layman Brook

NumberofFish

0

10

20

30

40

0

10

20

30

40

0

10

20

30

40

20

30

40

0

10

20

30

40

0

10

20

30

40

0

10

20

30

40

McAtee Brook

NumberofFish

0

10

20

30

40

0

10

20

30

40

0

10

20

30

40

20

30

40

Downstream

Upstream


2005October

November

December

2006February

March

June

August

2005October

November

December

2006February

March

June

August

DRY

DRY

DRY

NOT FLOWING

NOT FLOWING

n=58

n=68

n=37

n=10

n=113

n=60

n=25

n=0

n=22


54/185

log10 mean discharge (M3/sec)

-1.4 -1.2 -1.0 -0.8 -0.6 -0.4 -0.2 0.0

log10meanfrequ

encyoffish

0.6

0.7

0.8

0.9

1.0

1.1

1.2

1.3log10N = 0.39*log10D+ 1.19r2 = 0.91

Figure29 Relationshipbetween themean strength ofupstream migrationof Western

Minnows within the major flow period (August and December) and the

mean discharge in the four tributaries during that period. N.B. Data were

log10 transformed and migration was standardised for effort, see text for

details.

og10meanfrequencyoffish

1.0

1.2

1.4

1.6

1.8

2.0log10N = 0.74*log10D+ 1.89r2 = 0.95


55/185

55

Table4 CorrelationsbetweenupstreamanddownstreammovementofWesternMinnowsinthetributariesoftheBlackwoodRiverandprevailing

environmentalvariablesduringthemigrationperiod.N.B.Datawerelog10transformed,*denotescorrelationissignificantatthe0.05level

(2tailed).

Logtemperature

Logconductivity Log pH Log O2

Logdischarge

Upstreammovement



Log pH Pearson Correlation -.508 -.677

Sig. (2-tailed) .492 .323

Log O2 Pearson Correlation .229 .589 .182

Sig. (2-tailed) .771 .411 .818

Log discharge Pearson Correlation -.131 .600 -.573 .311

Sig. (2-tailed) .869 .400 .427 .689

Upstream movement Pearson Correlation -.129 .633 -.379 .563 .956*

Sig. (2-tailed) .871 .367 .621 .437 .044

Downstreammovement

Pearson Correlation.025 .666 -.747 .187 .973* .879

Sig. (2-tailed) .975 .334 .253 .813 .027 .121

Mud Mi o


56/185

MudMinnow

Habitatassociations

The Mud Minnow was only captured in the tributaries of the Blackwood

River(Appendix2)andthereforeisolationofthepopulationsinthesesystems

maybeoccurringwiththemainchanneleffectivelyactingasasaltbarrierto

population mixing; however, this requires further investigation. It was

recordedinPoisonGully,MilyeannupBrook,RosaBrookandMcAteeBrook;however,notinLaymansBrook(Appendix2). Thissuggeststhatthisspecies

prefers tributaries with either permanent (Milyeannup Brook and Psoin

Gully)orextended(RosaBrookandMcAteeBrook;thatbothhavesubstantial

remnant pools when they cease to flow) flow periods. Mud Minnows

naturallyexist in lowabundancescompared toothernativespecies (suchas

the Western Minnow) as was the case in this study with the speciesbeing

recordedinlowernumbersthananyothernativefreshwaterfish;andonly90individualsbeingcaptured. Morgan&Beatty(2005)alsoreportedthisspecies

in StJohn Brook and Red Gully. The upper reaches of Rosa Brook, which

receiveLeedervilleAquiferdischarge,areaknown refuge for thespecies in

thatsystem(Morganetal.2004a).

Migration

patterns

Due to the relatively low numbers of Mud Minnows, there were few clear

obvious trends in the movement patterns of this species in these systems

(Figure31). The largestnumbersrecorded infykenetswere inMilyeannup

Brook where on average 12 and six fish were recorded moving downstream


57/185

Meannumberoffish

0

5

10

15

20

Downstream movement

Upstream movement

Meannumberoffish

0

5

10

15

20

RosaBrook

Layman Brook

Meannumberoffish

0

5

10

15

20

25

30

Milyeannup Brook

beroffish

15

20

McAtee Brook

Mud Minnow (G. munda)

NF NF


58/185

0

2

4

6

8

10Downstream

Upstream

0

2

4

6

8

10

0

2

4

68

10

Rosa Brook

NumberofFish

0

2

4

6

8

10

0

2

4

6

8

10

0

2

46

8

10

8

10

0

2

4

6

8

10

Downstream

Upstream

0

2

4

6

8

10

0

2

4

6

8

10

Milyeannup Brook

Nu

mberofFish

0

2

4

6

8

10

0

2

4

6

8

10

0

2

4

6

8

10

8

10

2005October

November

December

2006February

March

June

August

2005October

November

December

2006February

March

June

August

Mud minnow (Galaxiella munda)

NOT FLOWING

NOT FLOWING

n=0

n=0

n=2

n=2

n=2

n=15

n=18

n=0

n=0

n=1

n=3

n=10


59/185

BalstonsPygmyPerch

Habitatassociations

Balstons Pygmy Perch is the most restricted fish species found within the

BlackwoodRivercatchmentandhasrecently(2006)been listedasVulnerable

undertheEPBCActandlistedbyCALMasSchedule1(WildlifeConservation

Act, 1950). Balstons Pygmy Perch was effectively only captured within

MilyeannupBrookwith3160of the 3177 fish (or99.46%)being recorded in

this stream; many of thesejuveniles with thebase population found tobemuch lessmuch less (seesectionMilyeannupBrookCaseStudy) (Figure33,

Appendix2). Thus,MilyeannupBrook is the crucial refugehabitat for this

speciesintheBlackwoodRivercatchment;probablyduetotheconsistencyof

suitable available habitat facilitated by the permanency of flow due to

groundwaterdischargeinthissystem.

FourindividualswerecapturedinMcAteeBrookduringAugust2006;whilea

further 13 fish were captured in Milyeannup Pool near the mouth of

Milyeannup Brook. The lengths recorded for this species in Milyeannup

Brook were considerably greater than has previouslybeen reported for the

species (see Morgan et al. 1995). The lengthfrequency distribution of this

species suggest that themodal lengthof the fish captured in August (5070

mmTL)arelikelytobe1yearold;whilethosefishgreaterthan70mmTLare

most likelyat theendof their secondor third year of life (Figure 34). The

relativelyhighlongevityoftheMilyeannupBrookpopulationcontrastswith

thoseelsewherethathaveonlybeenfoundtoliveforjustoveroneyear(see

Thus,thisupstreammigrationwasundoubtedlyadultsreadytospawn;likely


60/185

p g y y p y

moving upstream to offset the downstream movement of eggs and/or

larvae/juveniles. During September there was a considerable downstreammovement of spent (recently spawned) fish; suggesting the peak spawning

period was August in Milyeannup Brook. Subsequently, large numbers of

new recruits were captured moving downstream in November and

December.

During December a few individuals were captured near the mouth of

MilyeannupBrook(inthemainchannel)anditisevidentthatthesefishhadleftthestream. However,anumberalsomovedbackintothestreamatthis

time. DuringAugust,asmallnumberofadultswerealsocapturedmoving

upstreaminMilyeannupPool,presumablyontheirwaytoMilyeannupBrook

tocommencespawning(Figure35).

Meannum

beroffish

0

200

400

600

800Downstream movement

Upstream movement

Meannumberoffish

0

5

10

15

20

Rosa Brook

Layman Brook

beroffish

200

500

600

700

800

Milyeannup Brook

Balston's Pygmy Perch (N. balstoni)

NF NF


61/185

0

5

10

15

20

Downstream

Upstream

0

40

80

120

0

20

40

60

Milyeannup Brook

NumberofFish

0

5

10

15

20

0

5

10

15

20

0

5

10

15

20

20

30

40

2005October

November

December

2006February

March

June

August

Balston's Pgymy Perch (N. balstoni)


62/185

Meannumberoffis

h

0

20

40

60

80

100

Downstream movement

Upstream movement

Meannumberoffish

0

20

40

60

80

100

Denny Road

Milyeannup Pool

Meannumberoffish

0

20

40

60

80

100

Jalbarragup

roffish

60

80

100 Quigup

Baltston's Pgymy Perch (N. balstoni)

NS NS

h


63/185

WesternPygmyPerch

Habitatassociations

WesternPygmyPerchwererecordedmovingateachsitewithinRosaBrook,

MilyeannupBrookandMcAteeBrookoneachsamplingoccasion(Figure36).

This species was not captured in Layman Brook and very few were found

moving in the main channel sites; with none found migrating at the most

upstreamsite,Quigup(Figure37). Veryfewindividualswerecapturedinthe

main channel sites during the quantitative sampling (Appendix 1). This

suggeststhatthisspeciesislargelyreliantonthefreshwatertributariesinthis

region;reflectingarelativelylowtolerancetosalineconditions.

Migrationpatterns

BothupstreamanddownstreammovementsofWesternPygmyPerchwererecorded at most tributary sites on most sampling occasions (Figure 36).

Migration strength was greatest within Rosa Brook; which appeared to

support the largestpopulationofWesternPygmyPerchofany system. As

thisspeciesisknowntobreedinspring,itislikelythatmuchoftheupstream

migration impetus were for reproductive purposes. The subsequent

downstreammovementbythisspeciesinRosaBrookinDecember,aswellas

inMilyeannupBrookandMcAteeBrook,appearedtoconsistoffishthathad

spawned(i.e.spent)andwereleavingthesystemasflowsubsidedwithsome

newrecruitsalsobeingrecordedinMilyeannupBrook. However,withinthe

perennial Milyeannup Brook there continued to be upstream and

The upstream movement of the Western Pygmy Perch in tributaries was

iti l l t d ith di l d l l d i th fl


64/185

positively correlated with mean dissolved oxygen levels during the flow

period in the tributaries (althoughatasignificance levelofp


65/185

Meannumberoff

ish

0

5

10

15

20

Downstream movement

Upstream movement

Meannumberoffish

0

5

10

15

20

Denny Road

Milyeannup Pool

Meannumberoffish

0

10

20

30

40

Jalbarragup

eroffish

30

40 Quigup

Western Pygmy Perch (E.vittata)

NS NS


66/185

0

5

10 Downstream Migration

Upstream Migration

0

5

10

0

10

20

3040

50

60

Rosa Brook

NumberofFish

0

5

10

15

20

0

5

10

15

20

0

10

20

30

40

10

15

20

0

5

10

Downstream Migration

Upstream Migration

0

5

10

0

5

10

Milyeannup Brook

NumberofFish

0

5

10

0

5

10

0

5

10

5

10

2005October

November

December

2006February

March

June

August

2005October

November

December

2006February

March

June

August

Western Pygmy Perch (Edelia vittata)

NOT FLOWING

NOT FLOWING

n=19

n=18

n=194

n=64

n=27

n=11

n= 6

n=29

n= 6

n= 5

n=13

n=39


67/185

0

5

10

0

5

10

15

20

0

5

10

McAtee Brook

NumberofFish

0

5

10

15

20

0

5

10

15

20

0

5

10

40

50


2005October

November

December

2006February

March

June

August

n=12

n=54

n=19

n=18

155

NOT FLOWING

NOT FLOWING

Downstream

Upstream


68/185

0

2

4

6

8


Upstream Migration

0

2

4

6

8

10

0

2

46

8

10

NumberofFish

0

2

4

6

8

10

0

2

4

6

8

10

0

2

4

6

8

10

6

8

10

2005October

November

December

2006February

March

June

August


n=7

n=2

n=9

n=13

n=0

n=0

n=1


69/185

log10 mean dissolved O2 (ppm)

0.98 1.00 1.02 1.04 1.06

log10

meanfrequencyoffish

-1.5

-1.0

-0.5

0.0

0.5

1.0

log10N = 31.38*log10O2

- 32.06

r2

= 0.99

Figure41 Relationship between the mean strength of the upstream migration of

WesternPygmyPerch within the major flow period (August to December)

and the mean dissolved oxygen in the four tributaries during that period.

N.B.Datawerelog10transformedandmigrationwasstandardisedforeffort,

seetextfordetails.


70/185

70

Table5 Correlations between upstream and downstream movement of Western Pygmy Perch in the tributaries of the Blackwood River and

prevailingenvironmentalvariablesduringthemigrationperiod.N.B.Datawerelog10transformed.

Log

temperature

Log

conductivity Log pH Log O2

Log

discharge

Upstream

movement




Sig. (2-tailed) .492 .323


Sig. (2-tailed) .771 .411 .818


Sig. (2-tailed) .869 .400 .427 .689

Upstream movement Pearson Correlation .354 .868 .406 .991 .422

Sig. (2-tailed) .769 .330 .734 .088 .722

Downstreammovement

Pearson Correlation .493 .934 .262 .958 .279 .988

Sig. (2-tailed) .672 .233 .831 .185 .820 .098

Nightfish


71/185

Habitatassociations

The Nightfish was almost exclusively captured within the tributaries of the

BlackwoodRiver,whichaccountedfor99%ofcapturesofthisspecies(Figure

42, Appendix 2). As with the Western Pygmy Perch, the species therefore

appears tobe largely intolerant of conditions in the main channel of the

BlackwoodRiverandisreliantontributaryhabitats;particularlywithregards

tospawningandrecruitment.

Migrationpatterns

ThehighestnumbersofNightfishcaptured in fykenetswere fromLayman

Brook(629),largelyasaconsequenceofamassexodusofjuveniles(1020mm

TL)fromthissystemduringDecember(Figure42). Similarmovementswere

also recordedwithinMilyeannup Brookand Rosa Brook. Thedownstreammigration ispresumablya response toa reduction indischargeat that time

withassociatedwater levelandhabitatdecline. Upstreammigrationswere

more ambiguous, however in most systems there were relatively weak

upstream migrations in winter and early spring. There is evidence for an

earlierandmoreprotractedspawning (andrecruitment)periodofNightfish

inMilyeannupBrookaslargersizesofthemigratingjuvenileswererecorded

inthis tributary inDecember. Forexample,withinMilyeannupBrook these

new recruits ranged in length from 1039 mm TL in this month, compared

with1024mmTLinRosaBrookandLaymanBrook(Figures43,44).

movementofNightfish(Figure47). ThisrelationshipsuggeststhatNightfish

may prefer more highly oxygenated streams for spawning, although


72/185

undoubtedly other habitat parameters of these streams would also be of

importance(suchasdegreeofinstreamstructureforeggdeposition)andasa

daytimerefugetothisnocturnalspecies.

Meannum

beroffish

0

20

40

60

80

100

120

Downstream movement

Upstream movement

Meannumb

eroffish

0

50

100

150

200

250

300

350

Rosa Brook

Layman Brook

Meannumbe

roffish

0

50

100

150

200

Milyeannup Brook

Nightfish (B. porosa)

DRY DRY DRY

NF NF


73/185

0

5

10Downstream

Upstream

0

5

10

0

25

50

75

100

125

150

Rosa Brook

NumberofFish

0

5

10

0

5

10

0

5

10

5

10

0

5

10

Downstream

Upstream

0

5

10

0

10

20

3040

50

60

Milyeannup Brook

NumberofFish

0

5

10

0

5

10

0

5

10

5

10

2005October

November

December

2006February

March

June

August

2005October

November

December

2006February

March

June

August

Nightfish (Bostockia porosa)

NOT FLOWING

NOT FLOWING


74/185

0

5

10 Downstream

Upstream

0

5

10

0

50

100

150

200

Layman Brook

NumberofFish

0

5

10

0

5

10

0

5

10

5

10

0

5

10

0

5

10

0

5

10

McAtee Brook

NumberofFish

0

5

10

0

5

10

0

5

10

5

10

Downstream

Upstream


2005October

November

December

2006February

March

June

August

2005October

November

December

2006February

March

June

August

DRY

DRY

DRY

NOT FLOWING

NOT FLOWING


75/185

Meannumberoffish

0

10

20

30

Downstream movement

Upstream movement

Meannumberoffish

0

10

20

30

Denny Road

Milyeannup Pool

Meannumberoffish

0

10

20

30

Jalbarragup

fish

30 Quigup

Nightfish (B. porosa)

NS NS


76/185

0

2

4

6

8


Upstream Migration

0

2

4

6

8

10

0

2

4

6

8

10

NumberofFish

0

2

4

6

8

10

0

2

4

6

8

10

0

24

6

8

10

8

10

2005October

November

December

2006February

March

June

August


n=1

n=1

n=2

n=3

n=5

n=0

n=3


77/185

log10 mean dissolved O2 (ppm)

0.98 1.00 1.02 1.04 1.06

log10meanfrequencyoffish

-1.2

-1.0

-0.8

-0.6

-0.4

-0.2

0.0

0.2

0.4

0.6

log10N = 23.49*log10O2

- 24.30

r2

= 0.98

Figure47 RelationshipbetweenthemeanstrengthofupstreammigrationofNightfish

within the major flow period (August and December) and the mean

dissolvedoxygen in the four tributariesduring thatperiod.N.B.Datawere

log10 transformed and migration number was standardised for effort, see

textfordetails.


78/185

78

Table6 CorrelationsbetweenupstreamanddownstreammovementofNightfish intheBlackwoodRivertributariesandprevailingenvironmental

variablesduringthemigrationperiod.N.B.Datawerelog10transformed,**denotescorrelationissignificantatthe0.01level(2tailed).

Log

temperature

Log

conductivity Log pH Log O2

Log

discharge

Upstream

movementLog conductivity Pearson Correlation .686



Sig. (2-tailed) .492 .323


Sig. (2-tailed) .771 .411 .818


Sig. (2-tailed) .869 .400 .427 .689

Upstream movement Pearson Correlation .181 .552 .220 .999** .307

Sig. (2-tailed) .819 .448 .780 .001 .693

Downstreammovement

Pearson Correlation-.858 -.907 .831 -.248 -.380 -.201

Sig. (2-tailed) .142 .093 .169 .752 .620 .799

SouthwesternGoby


79/185

Habitatassociations

Although Southwestern Goby is typically encountered within estuaries,

duringthisstudy,itwasmostcommonlyrecordedwithinmostmainchannel

sites;accountingfor~92%ofcapturesofthisspecies(Figure48,Appendix1).

Asmallnumberofindividualsofwerealsocapturedinthelowerreachesof

Milyeannup Brook (eight) and Rosa Brook (14) (Figure 51). This species is

therefore largely reliant on the main channel habitats; an expected finding

given it is a known estuarine species and the main channel has become

salinised.

Migrationpatterns

In most months at the downstream main channel sites (receiving most

groundwaterdischarge), themajorityofSouthwesternGobiesweremovingdownstream(Figure48). DownstreammovementwasgreatestattheDenny

Road siteduringFebruary,when>100 fish/daywere captured. Thesewere

largelysmallfishthatwereprobablynewrecruits(1039mmTL)(Figures49,

50). The downstream movement of this cohort continued through to

September,with

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