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Fishandcrayfishcommunitiesof
theBlackwood
River:
migrations,
ecology,andinfluenceofsurface
andgroundwater
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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
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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.
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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
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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.
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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.
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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
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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
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Section 1
Migrationpatterns
of
the
fish
and
crayfish
fauna
of
theBlackwoodRiver
SJBeatty,FJMcAleer&DLMorgan
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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
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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
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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).
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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.
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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
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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)
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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.
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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
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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
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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
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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
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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)
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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
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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.
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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
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A
Month
Oct Nov Dec Feb Mar Jun Aug Sep
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
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Month
Oct Nov Dec Feb Mar Jun Aug Sep
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
Milyeannup Brook - downstream
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
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Month
Oct Nov Dec Feb Mar Jun Aug Sep
Dissolvedoxygen(ppm)
2
4
6
8
10
12
14
16
18
Rosa Brook
Laymans Brook
McAtee Brook
Milyeannup Brook - upstream
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
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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).
Oct Nov Dec Feb Mar Jun Aug Sep
Meandischarge(m3/sec
)
0
1
2
3
4Rosa Brook
Laymans Brook
McAtee Brook
Milyeannup Brook - upstream
Milyeannup Brook - downstream
Poison Gully
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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
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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.
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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
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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.
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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.
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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
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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
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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.
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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
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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.
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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
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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)
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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
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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
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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
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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)
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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
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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
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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
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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
Western Minnow (Galaxias occidentalis)
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
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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
Western Minnow (Galaxias occidentalis)
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
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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
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55
Table4 CorrelationsbetweenupstreamanddownstreammovementofWesternMinnowsinthetributariesoftheBlackwoodRiverandprevailing
environmentalvariablesduringthemigrationperiod.N.B.Datawerelog10transformed,*denotescorrelationissignificantatthe0.05level
(2tailed).
Logtemperature
Logconductivity Log pH Log O2
Logdischarge
Upstreammovement
Log conductivity Pearson Correlation .686
Sig. (2-tailed) .314
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
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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
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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
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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
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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
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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
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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)
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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
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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
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positively correlated with mean dissolved oxygen levels during the flow
period in the tributaries (althoughatasignificance levelofp
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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
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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
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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
Western Pygmy Perch (Edelia vittata)
2005October
November
December
2006February
March
June
August
n=12
n=54
n=19
n=18
155
NOT FLOWING
NOT FLOWING
Downstream
Upstream
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0
2
4
6
8
10 Downstream Migration
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
Western Pygmy Perch (Edelia vittata)
n=7
n=2
n=9
n=13
n=0
n=0
n=1
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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.
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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
Log conductivity Pearson Correlation .686
Sig. (2-tailed) .314
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 .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
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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
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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
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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
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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
Nightfish (Bostockia porosa)
2005October
November
December
2006February
March
June
August
2005October
November
December
2006February
March
June
August
DRY
DRY
DRY
NOT FLOWING
NOT FLOWING
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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
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0
2
4
6
8
10 Downstream Migration
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
Nightfish (Bostockia porosa)
n=1
n=1
n=2
n=3
n=5
n=0
n=3
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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.
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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) .314
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 .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
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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