APPLIED ISSUES Flow-related patterns in abundance and composition

APPLIED ISSUES

Flow-related patterns in abundance and compositionof the fish fauna of a degraded Australian lowland river

PAUL HUMPHRIES* , 1 , PAUL BROWN †, JOHN DOUGLAS †, ANDREW PICKWORTH†, 2 ,

RUSSEL STRONGMAN †, KYLIE HALL † AND LUCIANO SERAFINI*

*Department of Biological Sciences, Cooperative Research Centre for Freshwater Ecology, c/- Murray-Darling Freshwater Research

Centre, Monash University, Albury, NSW, Australia†Department of Primary Industries, Primary Industries Research Victoria, Alexandra, Vic., Australia

SUMMARY

1. A 7-year study was conducted in three hydrologically distinct sections within the highly

regulated, lowland Campaspe River to investigate the influence of hydrology on temporal

and spatial patterns in fish composition, abundance and recruitment. One section had

6 months, one section 2 months and one section no months of increased flow due to

storage releases. The fish fauna of the less regulated, nearby Broken River served as a

reference to which that of the Campaspe River was compared for the last 3 years of the

study to allow insight into the relative effects of hydrology, barriers to movement and

other environmental characteristics. The study included one high-flow year, a moderate-

flow year and five low-flow years.

2. A total of 16 fish species – 10 native and six alien – were caught in the Campaspe River,

although of the native species, only three are considered to have self-sustaining

populations. The remaining species are either itinerants or a result of stocking. Alien

species comprised approximately 64% of the total biomass of all fish caught.

3. Overall composition of the fish fauna did not differ significantly by year, but did by

section of river. Species richness and the abundance of most of the dominant species also

differed significantly by river section, but there was little inter-annual variation in the

abundance of any species, except for European perch and for common carp; the latter

showing an increase in abundance following a high-flow event during the spring of 2000 as

a result of recruitment.

4. Overall faunal composition was not influenced by hydrology. However, multiple

regression indicated that species richness, abundance of the dominant species and

abundance of young-of-year (YOY) of golden perch, European perch and common carp all

were influenced significantly by hydrological variables. The nature of the relationships

was dependent on river section and hydrological season (‘winter’ or ‘spring/summer’). Of

note was the result that the total abundance of fish and that of YOY common carp were

significantly positively related to the number of spells above the threshold for movement

upstream through the lower two weirs in the Campaspe River. Only one significant

Correspondence: Paul Humphries, School of Environmental Sciences, Institute for Land Water and Society, Charles Sturt University,

PO Box 789, Albury, NSW 2640, Australia.

E-mail: [email protected] address: School of Environmental Sciences, Institute for Land Water and Society, Charles Sturt University, PO Box 789,

Albury, NSW 2640, Australia.2Present address: Department of Sustainability and Environment, Arthur Rylah Institute for Environmental Research, PO Box 137,

Heidelberg, Vic. 3084, Australia.

Freshwater Biology (2008) 53, 789–813 doi:10.1111/j.1365-2427.2007.01904.x

� 2007 The Authors, Journal compilation � 2007 Blackwell Publishing Ltd 789

relationship between hydrological and fish-related variables was found for the upper river

section, whereas seven and five were found for the lower and middle sections respectively.

5. Comparisons with fish collected in the Broken River over 3 years suggest that the fauna

of the Broken River is in a more natural state than that of the Campaspe River. Since the

two rivers do not differ substantially in water quality, and since both contain significant

weirs, which act as barriers to movement of fish, flow regulation is most likely to be the

major reason for the poor state of the fauna in the Campaspe River.

Keywords: alien, Campaspe and Broken Rivers, flow regulation, hydrology, Murray-Darling Basin,recruitment

Introduction

Flow is the overriding force in rivers. Flow defines

river geomorphology and sediment transport, deter-

mines the type, amount and accessibility of habitat for

riverine animals and plants, it drives food webs

through transportation of carbon and it has a major

influence on animal and plant behaviour and life

histories (see Vannote et al., 1980; Frissell et al., 1986;

Junk, Bayley & Sparks, 1989; Calow & Petts, 1992;

Thorp & Delong, 1994; Matthews, 1998; Fausch et al.,

2002). The flow regime of a river can be described by

five major components: magnitude, duration, timing,

frequency and rate of change. These components

operate at a number of temporal and spatial scales,

and riverine biota have evolved in their context, and

must either take advantage of the predictable aspects

of the components, such as annual, widespread

flooding of forests in tropical South America, or deal

as best they can with the less predictable aspects, e.g.

summer spates or supra-seasonal droughts (Poff et al.,

1997; Lake, 2003; Richter et al., 2003). High flows, and

especially spates, seem to play a major role in

influencing the variability in fish assemblages, at least

in the short term (Oberdorff, Hugueny & Vigneron,

2001; Schiemer et al., 2001; Koel & Sparks, 2002; Li &

Gelwick, 2005).

River regulation is widespread throughout the

world and it typically alters one or more of the

components of a flow regime, depending on whether

the regulation exists for irrigation, hydroelectricity

generation, river transport or other purposes (Ward &

Stanford, 1979; Petts, 1984; Calow & Petts, 1992).

Riverine fishes are some of the more conspicuous

victims of river regulation, with flow alteration and

the structures which effect it, being implicated in

disrupting life histories, degrading habitat, impeding

movement, affecting food webs and so on (see Ward

& Stanford, 1979; Petts, 1984; Welcomme, 1985;

Walker, 1986, 1992; Matthews, 1998). The result of

this is, as a general rule, to alter the composition of

fish assemblages; with intolerant species declining in

abundance or becoming locally extinct and opportu-

nistic native and alien species often coming to dom-

inate (e.g. Gehrke et al., 1995; Aarts, Van den Brink &

Nienhuis, 2004; Lamouroux & Cattaneo, 2006). Barri-

ers to movement exacerbate the effects of flow

alteration by preventing movement into and out of

affected areas and preventing recolonization (Mat-

thews, 1998; Lucas & Baras, 2001).

Whilst many studies exist which highlight the likely

effects of river regulation on fish (see above reviews),

most have been of relatively short duration, which

limits their ability to draw meaningful conclusions.

Moreover, few are able to make definite links between

hydrology and characteristics of fish assemblages and

populations, such as composition, abundance/bio-

mass, recruitment and movement, because appropriate

spatial and/or interannual comparisons are unable to

be made (see Cattaneo et al., 2002; Daufresne et al., 2003

for notable exceptions). For example, although the

study by Gehrke et al. (1995) suggests that the more

altered the flow of a river is, the fewer natives species

and the greater the dominance by alien species, the

results are based on two sampling occasions (despite a

good geographic spread) and so questions remain

about temporal variation. It is only by conducting

multi-year studies, under a range of hydrological

conditions, such as floods, droughts and ‘average’

flows, that we are likely to be able to establish how

hydrology influences fish faunal characteristics (Lloyd

et al., 2003; Lytle & Poff, 2003). By so doing, this will

provide the type of knowledge needed for effective

management of regulated rivers.

790 P. Humphries et al.

� 2007 The Authors, Journal compilation � 2007 Blackwell Publishing Ltd, Freshwater Biology, 53, 789–813

Australian lowland rivers and their fish faunas, like

many throughout the world, are in a parlous state

(Murray-Darling Basin Commission, 2004). The highly

regulated Campaspe River, in northern Victoria, is

one example of a severely degraded river system,

with a fish fauna dominated by alien species and few

native species having self-sustaining populations

(Humphries & Lake, 2000; Humphries, Serafini &

King, 2002). The Campaspe River provides an oppor-

tunity to study the effects of flow alteration on a fish

fauna because, below the major regulating structure

(Lake Eppalock) there are three river sections, each

with its own distinct hydrology, all within about 175

river km from its junction with the Murray River at

Echuca. Lake Eppalock stores winter and early spring

runoff, releasing it at a later date, primarily for

irrigation purposes. Unless a major rainfall event

occurs, the ‘upper’ section of the Campaspe River

typically experiences highly regulated, enhanced

flows for 6 months over later spring-early autumn,

whereas the ‘middle’ section only receives enhanced

flow for about 2 months during autumn and the

‘lower’ section receives only minor ‘maintenance’

flows for most of the year.

We present here the results of a 7-year study of the

Campaspe River below Lake Eppalock, in which we

compare the fish faunas in the three hydrologically-

distinct river sections. We were thus able to investi-

gate the role of river section (with contrasting

hydrologies) and year (the period of the study

included one high-flow, one moderate-flow and five

low-flow years), focusing on components of the fauna

which we considered would give us insight into the

role of hydrology in structuring fish assemblages and

populations (species composition, abundance/bio-

mass and recruitment) and correlated these with

hydrological variables. To strengthen our study fur-

ther, we included, in the final 3 years of the study, a

comparison of the fish fauna of the Campaspe River

with that of the much less regulated nearby Broken

River. This has allowed us to speculate on how much

of an effect barriers to movement, since both rivers

contained significant weirs, and other environmental

variables had on characteristics of the fish faunas from

each river.

The current paper thus aims to (i) determine how

the composition, species richness, abundance and

biomass of the fish fauna of the Campaspe River

varied among the three hydrologically distinct sec-

tions of river and among the 7 years of the study, with

the prediction that the greater the degree of flow

alteration, the fewer species and the greater the

dominance of alien species; (ii) relate characteristics

of the fish fauna (specifically, composition, species

richness, abundance of dominant species and juvenile

recruitment) to hydrological variables (high, low,

average and threshold flows for fish passage up-

stream of weirs) of the Campaspe River among the

three river sections and for two seasons (‘winter’ and

‘spring/summer’), with the prediction that the fish-

related variables will respond more to high and

threshold flows because of greater ability for fish to

move between river sections during these times; and

(iii) compare the composition, species richness, abun-

dance and biomass of fish in the Campaspe River with

that of the less regulated and nearby Broken River,

with the prediction that there will be more native

species, and that they will comprise a larger propor-

tion of the fish fauna, in the Broken than in the

Campaspe River. We emphasize spatial and temporal

differences and also speculate on the proximate and

ultimate roles of flow in shaping the Campaspe River

fish fauna.

Methods

Study area and hydrology

The Campaspe River is located in the southern

Murray-Darling Basin and is a tributary of the Murray

River (Fig. 1). Since the early 1960s, c. 50% of the

mean annual discharge of about 2 · 108 m3 has been

stored in Lake Eppalock for later release downstream

(Fig. 2a). The river downstream of Lake Eppalock can

be divided into three sections, based on hydrology

and the presence of weirs: the ‘upper’ section from

Lake Eppalock to Campaspe Weir (c. 9 m high); the

‘middle’ section from Campaspe Weir to Campaspe

Siphon (c. 2 m high) and the ‘lower’ section from

Campaspe Siphon to the confluence with the Murray

River (Fig. 1). There is also a small, c. 1 m high,

gauging weir in the Campaspe River, near Echuca.

The entire river downstream of Lake Eppalock expe-

riences reduced duration of high winter flows due to

the capture of water (Fig. 2a). In addition, the upper

and middle sections of the river experience approx-

imately 6 and 2 months, respectively, of enhanced

summer flows because of irrigation releases. Most of

Regulated river fish fauna 791


this irrigation flow is extracted from the river at the

Campaspe Siphon and so the lower section has only

marginally enhanced flows at this time. Prior to our

study, Lake Eppalock filled and spilled approximately

every 2 years during which time high flows would

pass down the entire length of the river (Fig. 2b). This

only occurred once, early in the present study. Before

the construction of Lake Eppalock and the weirs (pre-

regulation), the Campaspe River would have ceased

to flow during the dry summer period in most years.

This no longer occurs.

Long (up to 1 km), deep (up to 8 m) and still or very

slow flowing natural pools are common in the upper

section of the Campaspe River and are separated by

relatively shallow (0.3–1.5 m), still to moderate veloc-

ity (0–0.5 m s)1) run habitats. The middle and lower

sections of the river have no large natural pools and

consist mostly of run habitat, characterized by alter-

nating shallow (<1 m) and deep (1–3 m) regions. The

river immediately downstream of Lake Eppalock is

typically 30–40 m wide, with high banks and few

anastomosing channels or oxbow lakes. Further

downstream, the river becomes less constrained

(40–50 m wide mostly), in places it has multiple

channels and is more likely to move out on to the

floodplain. The dominant instream structure is coarse

woody debris (or ‘snags’) mainly from riparian river

redgums, Eucalyptus camaldulensis (Dehnhardt) and

stands of aquatic macrophytes, mostly common reed,

Phragmites australis (Cav). Records indicate that the

Campaspe River once supported approximately 20

species, however, recent evidence suggests that the

fish fauna is now highly degraded, and dominated by

the alien species common carp, Cyprinus carpio L, and

European perch, Perca fluviatilis L (Humphries &

Lake, 2000; Humphries et al., 2002).

Between 1993 and 2002, approximately 182 000

golden perch juveniles (0.8–1.6 g) were released into

the Campaspe River below Lake Eppalock: 20 000–

45 000 were stocked each year except in 1996 and

1997. Official records indicate that stocking of Murray

cod juveniles in the Campaspe River below Lake

Eppalock only took place in 2001 (5000 upper, 10 000

lower section), 2002 (19 000 juveniles and 25 1 year

olds, middle section) and 2003 (10 000 upper and

middle sections).

The Broken River is a tributary of the Goulburn

River, which itself is a tributary of the Murray River

(Fig. 1). It was chosen as a reference river with which

to compare the fish fauna of the Campaspe River,

because it is less regulated than the Campaspe River,

with a smaller fraction of its mean annual discharge of

2 · 108 m3 diverted for offstream use and responds

more naturally to rainfall events in the catchment than

does the Campaspe River (Smith & Humphries, 1997).

The impoundments, Lakes Nillahcootie (built 1967)

and Mokoan (built 1971), are the primary regulating

bodies in the Broken River. Two weirs (Casey and

Fig. 1 Map of Campaspe and Broken Rivers, showing major

storages and delineating upper, middle and lower sections of

each river included in study.

0

5

10

15

0

5

10

15

Jan Mar May Jul Sep NovMonth

Dis

char

ge (

m3 s

–1)

Pre-dam

Post-dam

(a)

(b)

Fig. 2 Median mean monthly discharges for the (a) upper

section and (b) lower section of the Campaspe River prior to the

construction of Lake Eppalock (pre-dam, 1885–1908) and after

the construction of Lake Eppalock (post-dam, 1977–94).



Gowangardie Weirs, both c. 3 m high) downstream of

the major impoundments, whilst creating pools

upstream and inhibiting fish movement, have a

relatively small effect on the hydrology of the river.

The Broken River was similarly divided into three

sections: Benalla Weir to Casey Weir, the ‘upper’

section; Casey Weir to Gowangardie Weir, the

‘middle’ section and Gowangardie Weir to the

confluence with the Goulburn River at Shepparton,

the ‘lower’ section (Fig. 1). The Broken River channel

width is marginally smaller than the Campaspe

(typically 25–35 m) and has no large natural pools

comparable to those in the upper Campaspe River,

however, the run habitat is similar to the Campaspe,

comprising alternating shallow (<1 m) and deep

(1–3 m) areas with still to moderate velocities

(0–0.5 m s)1). Instream structure similarly comprises

snags, derived from riparian river redgums, and

aquatic macrophytes, dominated by common reed.

Historically, the Campaspe and Broken Rivers

would have had a similar suite of fish species

(Humphries & Lake, 2000). The native fish fauna of

the Broken River has no doubt also suffered as a result

of a variety of anthropogenic disturbances, however,

nowadays there are still approximately 12 native

species extant in the Broken River, with several large

and small native species present in significant

numbers (Humphries & Lake, 2000). Stocking of

golden perch (0.8–1.5 g) also occurred in this river

during the current study at the rate of, typically,

20 000 juveniles annually (Victorian Department of

Primary Industries, unpubl. data). In 1993 there were

no records of golden perch being stocked, and in 2002,

9000 juveniles and 25 1-year-old fish were stocked.

Collection and processing of fish

Fish were collected from two reaches, randomly

chosen from a range of possible reaches, on each

occasion, from within each section of the Campaspe

River bimonthly between October 1995 and June 2000.

Because of changes in funding, between August 2000

and February 2003 the sampling frequency decreased

to four times per year: February, June, October and

December. During the latter period, sampling also

included two randomly chosen reaches within each

section of the Broken River. The Campaspe and

Broken Rivers were sampled within the same week

on each occasion and following identical protocols.

Thus our sampling consisted of a total of eight

replicates per section per year, including four from

each reach. This frequency of sampling is twice and

sometimes four times that of most comparable studies

(e.g. Gehrke et al., 1995) and it encompasses the warm

and cool, wet and dry and non-breeding and breeding

times of the year.

Sampling over the first year of the study using large

and small fyke nets, bait traps, seines, dip nets and

back-pack and boat electrofishers indicated that a

combination of large and small fyke nets was able to

be used in a consistent manner, and was able to be

deployed in all river conditions and captured juve-

niles and adults of the large-bodied species and most

of the smaller-bodied species in similar proportions to

a combination of all the other methods trialled. Fyke

nets were not efficient in catching Australian smelt or

gambusia, which were better collected using light

traps and/or other active methods (see Humphries

et al., 2002 and P. Humphries & A. Richardson,

unpubl. data). Therefore, fish were collected using a

combination of seven large fyke nets (35 mm mesh,

0.5 m diameter mouth, 3 m long, 5 m central wing)

and three small fyke nets [4 mm mesh, 0.5 m mouth

(with 30 mm mesh at front to prevent large fauna

from entering), 1.3 m long, 3 m central wing]. Nets

were set facing downstream at an angle to the bank,

randomly along a 100–350 m reach, approximately

3 h before dusk and retrieved within approximately

4 h after dawn the next day.

Opportunistic electrofishing sampling by backpack

(Smith-Root model 15-C POW and model 12-A;

Smith-Root, Vancouver, WA, U.S.A.) and boat

(Smith-Root model 5.0 GPP; Smith-Root, Vancouver,

WA, U.S.A.) was undertaken between October 1995

and June 2000. However, because this method could

not be carried out consistently due to frequent

difficulties gaining access to the river, the results

from this sampling are only included in a description

of the presence of species in the river as a whole, over

time (Fig. 4) and were not included in any other

analyses.

Fish were anaesthetized, identified to species,

weighed to 1 g (if fish were less than 1 g, they were

pooled and the total weight of that species for a net was

determined) and measured to 1 mm. All fish, except

common carp (which, by law must be destroyed), were

then allowed to recover in clean water, before being

returned to the river. It is recognized that some small



species will not be sampled as efficiently by fyke nets as

other gear (see below in Discussion), but the consis-

tency of sampling for all reaches and sampling occa-

sions using fyke nets allows for meaningful

comparisons throughout the entire study.

Environmental and hydrological data

Duplicate measurements of temperature, dissolved

oxygen, turbidity, conductivity and pH were taken at

each reach on each sampling occasion using a Horiba�

Water Checker U-10 (Horiba, Kyoto, Japan).

Hydrological data were obtained from Goulburn-

Murray Water through gauging stations operated by

Thiess Environmental Services. Gauging stations are

located at Lake Eppalock, Campaspe Weir and

Campaspe Siphon on the Campaspe River (thus

providing flow records for each of the three sections

of the river) and at Benalla and Casey Weir on the

Broken River (only providing flow records for the

upper section and the combined middle and lower

sections) (Fig. 1).

Analysis of fish data

The occurrence of species of fish in the Campaspe

River over time was described by the presence or

absence of species derived from samples collected

using backpack and boat electrofishing and large and

small fyke netting. All other analyses were carried out

on fyke net data only (seven large and three small

fyke nets per reach), since these were employed

consistently throughout the entire study.

Relative contribution of species to the fish fauna

was used as an overall descriptor of the fauna and

was derived from fish abundance and biomass data

for each section of the Campaspe River, calculated

from the summed values of fish collected in two

reaches within that section (from 14 large and six

small fyke nets per section per sampling trip) for the

entire study period (October 1995–February 2003).

Relative contribution of species to the Broken River

fish fauna, between August 2000 and February 2003,

were calculated in the same way and were compared

with data from the Campaspe River obtained during

the same period.

An overall description of the fish fauna of the

Campaspe River over time and space was performed

using non-metric multidimensional scaling (NMDS)

analysis on fish abundance data collected using fyke

nets. Rare species were excluded from the NMDS; rare

species were those that occurred in samples only once.

Data were log10(x + 1) transformed and a Bray-Curtis

dissimilarity matrix calculated. Fifty random starts

were used. To determine whether fish assemblages

differed significantly with ‘Year’ and ‘Section’ two-way

analysis of similarity (ANOSIMANOSIM) was carried out. A

‘year’ was defined as being a spawning year: beginning

in August of 1 year and ending in June of the following.

NMDS and ANOSIMANOSIM were carried out using the

PRIMER V5 package (Clark & Warwick, 2001).

To determine if species richness and abundance

differed significantly over the 7-year study period and

among river sections in the Campaspe River, four of

the bimonthly sampling occasions per year were used

as replicates (June, October, December and February),

since these were sampled for the entire study period.

Two-way ANOVAANOVAs were carried out examining the

effects of ‘Year’ and ‘Section’ on species richness,

mean abundance of total fish, common carp, golden

perch, European perch and flathead gudgeon. These

four species were the only species collected in suffi-

cient abundance to allow such a comparison. Richness

data met the assumptions of ANOVAANOVA and so raw

values were used, whereas abundance data were

log10(x + 1) transformed to satisfy the assumptions of

ANOVAANOVA.

Recruitment

Recruitment was investigated by determining the

number of young-of-year (YOY) fish collected in any

1 year. A ‘recruitment season’ was assumed to begin

approximately 2 months after the commencement of

spawning (although, in the case of golden perch, this

was not possible, because no larvae were ever

collected), when fish would have become juveniles

and it is assumed that they would have already

suffered the bulk of mortality, and to finish before

spawning commenced in the following season. Thus,

the ‘recruitment season’ for common carp and Euro-

pean perch was designated from October to June and

for golden perch, from December to June. YOY carp

were designated as fish up to 125 mm (Brumley, 1996;

Villizi & Walker, 1999), YOY European perch as fish

up to 100 mm (Shafi & Maitland, 1971) and YOY

golden perch as fish up to 200 mm (Anderson,

Morison & Ray, 1992).



Relationships between hydrological and fish variables

The Echuca gauging weir is only about 1 m in height,

but its ‘drowning-out’ is a function of discharge of

both the Campaspe River and that of the Murray

River, since the waterlevel backs up the Campaspe,

when the Murray River runs high. Analysis of

hydrological data, consultation with Goulburn-

Murray Water hydrologists and personal observations

suggest that a discharge of approximately

23.15 m3 s)1 or above in the Campaspe River would

make upstream fish passage possible. The Campaspe

Siphon is constructed of a single, concrete apron,

rounded in section and set between relatively steep

banks. It is estimated that this structure, despite being

higher than the Echuca weir, is similarly ‘drowned-

out’ at approximately 23.15 m3 s)1, and personal

observations suggest that the discharge at which

upstream fish passage is possible would be at this

level or marginally lower. Thus, 23.15 m3 s)1 is taken

as the threshold level above which upstream fish

passage from the lower section to the middle section

of the Campaspe Rivers is possible. It is estimated

from field observations and confirmed by hydrolo-

gists from Goulburn-Murray Water, that upstream

fish passage through the 9 m Campaspe Weir would

be possible at around 185.18 m3 s)1, which is close to

minor flood level (c. 243.06 m3 s)1; B. Viney, pers.

comm.). It is at this discharge that there is sufficient

flow over and around the weir to provide a range of

velocities likely to allow fish passage. Thus,

185.18 m3 s)1 is taken as the threshold level above

which upstream fish passage from the middle section

to the upper section of the Campaspe Rivers is

possible. It is presumed, for the purposes of this

study, that downstream passage over all weirs is

possible at all times.

To relate the hydrology of the Campaspe River with

characteristics of the fish fauna (composition, species

richness, abundance and recruitment), a number of

hydrological variables were calculated (Table 1).

Analysis was conducted using the River Analysis

Package 2.0.1 (Marsh, Stewardson & Kennard, 2003).

Two periods of the year were chosen for separate

analysis, representing the ‘winter’ or non-growing

season (April–July) and the ‘spring/summer’ or

growing season (August–March), in a similar manner

to Cattaneo et al. (2002). The hydrology of each river

section – upper, middle and lower – was treated

separately. Hydrological variables were chosen to

take into account high (maximum flow, number and

duration of 10th percentile flows), low (minimum

flow, number and duration of 90th percentile flows),

median and variability of flows, as well as number

and duration of spells above threshold levels of

23.15 m3 s)1 (which is estimated as the flow above

which upstream fish passage is possible over the 1 m

Echuca gauging weir and the 2 m Campaspe Siphon,

see below) and 185.18 m3 s)1 (which is estimated as

the flow above which upstream fish passage is

possible over the 9 m Campaspe Weir).

Aspects of the fish fauna of the Campaspe River

were related to hydrological variables in two ways.

Firstly, a BIOENV analysis was performed on the

NMDS carried out earlier; BIOENV compares envi-

ronmental data, in this case the hydrological variables

described above, with the dissimilarity matrix derived

from the fish data by maximising a rank correlation

between their respective (dis)similarity matrices (PRI-

MER V5 package, Clark & Warwick, 2001). This was

done for the ‘winter’ and ‘spring/summer’ periods

separately. Secondly, a series of stepwise multiple

regressions was carried out to determine the effects of

the hydrological variables (as described above,

Table 1) on species richness, log10(x + 1) transformed

total abundance of all fish and the total abundance of

the dominant species (common carp, European perch,

golden perch, flathead gudgeon) and log10(x + 1)

transformed total abundance of recruits, i.e. YOY

common carp, European perch and golden perch. The

7 years were used as replicates. Each river section and

hydrological season (winter and spring/summer) was

analysed separately.

All analyses, except NMDS, ANOSIMANOSIM and BIOENV

were performed using Excel 2002 (Microsoft Inc.,

Sydney, NSW, Australia) and SPSS Version 14 (SPSS

Inc., Chicago, IL, U.S.A.).

Results

Environmental and hydrological variables

For virtually the entire seven and a half-year period of

the study, the Campaspe River experienced the failure

of normal winter rains (Fig. 3a). Only at the com-

mencement of the study, in the winter of 1996, and to

a lesser degree in the winter of 2000, was there

substantial runoff into the river, causing significant



rises in flow, not attributable to irrigation releases.

Irrigation releases took place in each year of the study,

generally between October and May in the upper

section of the river and for a shorter period in the

middle section. Releases from Lake Eppalock gener-

ated enhanced flow along the lower section over the

summer in the order of 0.35–0.46 m3 s)1, compared

with the 3.5–4.6 m3 s)1during this time in the upper

section.

The Campaspe River in the lower and middle

sections experienced zero flows on several occasions:

in the winter of 1996 and spring/summer of 1997 in

the lower section and in spring/summer and winter

in 1998 and winter of 1998 in the middle section

(Appendix). The upper section never experienced

zero flows. The Campaspe River reached the

23.15 m3 s)1 threshold three times in the spring/

summer of 1996 for a total duration of 34–35 days in

each river section and once or twice in the winter of

the same year, for a total of 13 days. This threshold

was also reached in the spring/summer of 2000, two

to three times, but this time only for a duration of

3–4 days. The threshold of 185.18 m3 s)1 was reached

only in the spring/summer of 1996 twice for a total of

3 days in the middle and upper sections.

Water temperature each year fell to a minimum of

7–8 �C usually in June and a maximum of 20–24 �C

usually in January (Fig. 3b). The upper section of the

Campaspe River experienced water temperatures

1–2 �C cooler than the lower and middle sections

during most summer months, whereas this difference

decreased or occasionally was reversed during the

winter months. There was a trend in the lower section

of the river for slightly higher temperatures in

summer and slightly lower temperatures in winter

compared with the middle section of the river.

Conductivity ranged from approximately 300 to

2000 lS cm)1 in the lower section, from 300

to 1300 lS cm)1in the middle section and from

300 to 1100 lS cm)1 in the upper section of the

Campaspe River between 1995 and 2003 (Fig. 3c).

There was typically an increase in conductivity from

the upper section to the lower section of the river. Most

notable, however, was the lower conductivity of the

water in the upper section, relative to the other two

sections.

Turbidity generally fluctuated between 10 and 50

NTUs during the study period, although there were

spikes of considerably higher turbidity at times

(Fig. 3d). In some cases these spikes were attributable

to rainfall events (e.g. in 2000), but at other times there

was no obvious cause. Turbidity in general increased

with distance downstream from Lake Eppalock.

Dissolved oxygen varied predictably with tempera-

ture, rarely dropping below 5 mg L)1 and rarely

exceeding 10 mg L)1 (Fig. 3e). Presumably, for this

reason, dissolved oxygen tended to be lower in

summer in the lower section than in the upper section

Table 1 Hydrological variables, their abbreviations and definitions, used in exploring relationships between characteristics of the

Campaspe River fish fauna and hydrology. The 23.15 m3 s)1 threshold is discharge above which it is estimated that fish can move

upstream past the lower two Campaspe River weirs and the 185.18 m3 s)1 threshold is the discharge above which it is estimated that

fish can move upstream past the upper weir

Hydrological variable Abbreviation Definition

Overall statistics

Maximum MAX Maximum flow during the 7-year study period

Minimum MIN Minimum flow during the 7-year study period

Median MED Median flow during the 7-year study period

Variability VAR Variability of flow during the 7-year study period ¼ range (10th–90th percentile)

divided by the median

No. low spells NSPELLLOW No. of spells below the 90th percentile for the 40-year flow regulation period

Duration of low spells DSPELLLOW Duration of spells below the 90th percentile for the 40-year flow regulation period

No. high spells NSPELLHIGH No. spells above the 10th percentile for the 40-year flow regulation period

Duration of high spells DSPELLHIGH Duration of spells above the 10th percentile for the 40-year flow regulation period

23.15 m3 s)1 threshold

No. spells NSPELL23 No. spells above 23.15 m3 s)1 for the 7-year study period

Duration of spells DSPELL23 Duration of spells above 23.15 m3 s)1 for the 7-year study period

185.18 m3 s)1 threshold

No. spells NSPELL185 No. of spells above 185.18 m3 s)1 for the 7-year study period

Duration of spells DSPELL185 Duration of spells above 185.18 m3 s)1 for the 7-year study period



and vice versa in winter. pH was generally between 7

and 8 in all sections of the Campaspe River during the

study and there were no consistent differences among

river sections (Fig. 3f).

Composition of the Campaspe River fish fauna

A total of 16 species, 10 native and six alien, were

recorded from the Campaspe River between October

5

6

7

8

9

O J A S D M A N F J O J A S D M A N F J O J A D

0

(f)

5

10

15 (e)

0

50

100

150 (d)

0500

1000150020002500

05

1015202530

(c)

(b)

1995 1996 1997 1998 1999 2000 2001 2002

(a)

pHD

isso

lved

oxy

gen

(mg

L–1)

Tur

bidi

ty (

NT

U)

Con

duct

ivity

(µS

cm

–1)

Tem

pera

ture

(°C

)D

isch

arge

(m

3 s–1

)

Date

0

10

20

30

40

50

60

Fig. 3 Discharge, temperature, conductivity, turbidity, dissolved oxygen and pH measurements taken for the upper (dotted line),

middle (dashed) and lower (solid) sections of the Campaspe River between October 1995 and February 2003. Vertical dashed line

represents when bimonthly sampling changed to sampling in October, December, February and June.



1995 and February 2003 (Fig. 4). Four native species,

flathead gudgeon (Philypnodon grandiceps [Krefft]),

Australian smelt (Retropinna semoni [Weber]), carp

gudgeons (Hypseleotris spp.; species have been com-

bined because of taxonomic uncertainties [Bertozzi

et al., 2000]) and golden perch (Macquaria ambigua

[Richardson]), and three alien species, common carp

(Cyprinus carpio L.), European perch (Perca fluviatilis

L.) and mosquitofish (Gambusia holbrooki [Girard]),

were collected consistently throughout the entire

study period. The native Murray cod (Macullochella

peelii peelii [Mitchell]) and the alien goldfish (Carassius

auratus L.) were collected less consistently, but on at

least half of the sampling trips. Several native species

were recorded only rarely.

A total of 1972 fish were collected over the study

period, with approximately 40% of them flathead

gudgeons, 19% European perch, 18% common carp

and 12% golden perch (Table 2). Overall, native fish

comprised a little more than half of all fish recorded.

By contrast, only about 1/3 of the total biomass of

370 kg of fish recorded was made up of native species.

Almost half of the total biomass was common carp,

approximately 33% was golden perch and 14% was

European perch.

More than twice the number of fish were recorded

from the lower and middle sections of the Campaspe

than from the upper section (Table 2). This was a

result of the relatively high abundance of golden

perch, common carp and European perch in the lower

section and a result of the contribution of flathead

gudgeon, primarily, and golden perch, secondarily, in

the middle section. Flathead gudgeon dominated the

abundance of fish recorded from the middle and

upper sections, whereas flathead gudgeon, common

carp and European perch contributed approximately

equally to the abundance of fish from the lower

section. Golden perch made up just over 10% in all

three sections of the river. Native species contributed

the least in the lower section, making up only 39% of

the abundance of fish recorded and the most in the

middle section, making up approximately 75% of the

total. Species richness declined from the lower section

to the upper section of the Campaspe River, with only

two native species recorded from the upper section.

Murray cod and carp gudgeons were absent from the

upper Campaspe section.

The biomass of fish was greatest in the lower

section of the Campaspe River, totaling approximately

162 kg, with the totals in the other two sections each

Native

Flathead gudgeonAustralian smelt

Carp gudgeonsGolden perch

Murray codSilver perch

Mountain galaxiasSpotted galaxiasMacquarie perch

Flatheaded galaxias

Alien

Common carpEuropean perch

Eastern gambusiaGoldfish

Brown troutWeatherloach

O D F A J A O D F A J A O D F A J A O D F A J A O D F A J A O D F A J A O D F A J A O D F

1995 1996 1997 1998 1999 2000 2001 2002 2003Date

Dis

char

ge (

m3

s–1)

0

10

20

30

40

50

60

Fig. 4 Occurrence of native and alien fishes in the Campaspe River, as recorded during fyke netting and electrofishing, superimposed

over discharge between October 1995 and February 2003. Gaps in the figure after June 2000 (dashed line) exist because bimonthly

sampling changed at this time to sampling in October, December, February and June.



approximately 100 kg (Table 2). Common carp con-

tributed the most biomass to the fauna in each river

section (44–48%), with golden perch second

(29–37%). The only other species to contribute more

than 10% was European perch. Native species com-

prised 33–39% of the total biomass of fish from each

reach. Common carp and European perch together

comprised approximately 60% in each reach.

Non-metric multidimensional scaling analysis and

ANOSIMANOSIM of the fish abundance data for the 7 years

and three river sections indicated that there were

different assemblages among sections (global

R ¼ 0.231, P < 0.01), but not among years (global

R ¼ )0.185, P > 0.05) (Fig. 5). Post hoc comparisons

showed that there was no difference in the assem-

blages between the lower and middle sections (R ¼0.086, P > 0.05), but there were differences between

the lower and upper sections (R ¼ 0.285, P < 0.05)

and the middle and upper sections (R ¼ 0.357,

P < 0.01).

1996

1997

1998

1999

2000

2001

2002

1996

1997

1998

1999

2000

2001

2002

1996

1997

1998

19992000

20012002

Stress: 0.2

Lower

Middle

Upper

Fig. 5 Non-metric multidimensional

scaling analysis plot of fish assemblage

data for the three sections and 7 years

from the Campaspe River.

Table 2 Percentage abundance and biomass, total abundance and biomass,% natives, species richness total and% species richness of

natives of fish collected in the Campaspe River between October 1995 and June 2003

Species

Lower Middle Upper Total

No. Biomass (kg) No. Biomass (kg) No. Biomass (kg) No. Biomass (kg)

Native

Flathead gudgeon 25.1 0.3 56.9 0.9 52.8 0.4 43.0 0.5

Golden perch 12.7 37.1 11.6 29.1 12.3 32.6 12.2 33.6

Carp gudgeons 0.7 <0.1 1.7 <0.1 1.0 <0.01

Murray cod 0.4 1.3 2.3 5.8 1.1 2.2

Australian smelt 0.1 <0.1 2.2 <0.1 0.9 <0.01

Silver perch 0.1 <0.1 0.1 0.1 <0.01

Flatheaded galaxias 0.1 <0.1 0.1 <0.01

Alien

Common carp 30.6 46.7 8.1 43.8 10.2 47.9 17.8 46.2

European perch 25.6 11.2 12.3 19.1 18.4 11.9 19.0 13.6

Goldfish 3.3 3.3 1.3 1.2 4.5 2.8 2.7 2.6

Eastern gambusia 1.1 <0.1 3.3 <0.1 1.8 <0.01

Brown trout 1.8 4.5 0.4 1.2

Carp/goldfish hybrid 0.1 <0.1 0.1 <0.01

Total 812 161951 778 104206 381 103068 1972 369225

Natives (%) 39.2 38.8 74.8 35.8 65.1 33 58.3 36.3

Species richness total 12 11 6 13

Species richness natives (%) 58.3 54.5 33.3 53.8



Species richness and abundance of dominant species

Species richness and the abundance of total fish and

flathead gudgeons varied significantly with section of

river, whereas abundance of common carp and

European perch varied with section and year (Table 3,

Fig. 6). In the case of species richness and all species,

the mean square was greatest for section. Interaction

terms for all variables were non-significant and

abundance of golden perch did not vary significantly

with either factor. There were more species in the

lower and middle sections than in the upper section

(Tukey’s test, P < 0.001 and P < 0.01, respectively),

but there were similar numbers of species collected in

the lower and middle sections. For total fish, common

carp and European perch, Tukey’s test indicated that

there were significantly more fish in the lower section

than in the upper section of the Campaspe River

(P < 0.01). There were also more total fish and

flathead gudgeons in the middle section than in the

upper section of the river (P < 0.05 and P < 0.01,

respectively) and more common carp and European

perch in the lower section than in the middle section

(P < 0.05 and P < 0.01 respectively). There was evi-

dence for a gradual, but consistent decline in abun-

dance of European perch from 1996 until 2002,

whereas the abundance of common carp declined

from 1996 to 1999, increased in 2000 and subsequently

declined again to February 2003 (Fig. 6).

Recruitment

Common carp, European perch and golden perch

were the only species which were caught consistently

and in sufficient numbers to adequately examine

patterns in population structure (0+ versus ‡1+) and

recruitment. There were almost no YOY carp collected

in the upper section of the Campaspe River through-

out the entire study, only a small number in the

middle section and highly variable, but sometimes

large numbers in the lower section (Fig. 7a). YOY carp

were highly abundant and dominated the carp pop-

ulation in the 2000/01 season and made up approx-

imately 50% of the fish collected in the 1996/97

season.

In a similar pattern to carp, there were virtually no

YOY European perch in the upper section and very

few in the middle section of the Campaspe River

throughout the study period (Fig. 7b). Only in the first

year of the study were YOY collected in the middle

section, and these made up approximately 1/3 of all

fish collected in that season. By contrast, YOY Euro-

pean perch were collected in most years in the lower

section of the river. Furthermore, apart from the

2000/01 and 2001/02 seasons, the abundance of YOY

European perch in the lower section was relatively

consistent among years.

There were small numbers of YOY golden perch

collected in most years in each of the three sections of

the Campaspe River during the study period (Fig. 7c).

Only in 1996/97 in the lower section were YOY

golden perch reasonably abundant and made up a

substantial proportion of all fish collected.

Relationships between hydrological and fish variables

The BIOENV analysis relating fish assemblage com-

position with hydrological variables, using all 7 years’

data, but for each section separately, indicated that

there were no significant relationships either for the

‘winter’ or the ‘spring/summer’ seasons (Spearman’s

r ¼ 0.127 and r ¼ 0.108 respectively). However, when

multiple regressions were carried out relating species

richness, the abundance of individual species and the

abundance of YOY common carp, European perch

and golden perch with the hydrological variables,

several significant relationships were found (Table 4).

The fish variables that were positively related to high

flow variables were golden perch, European perch

(lower section, winter), and common carp and species

Table 3 Mean squares and significance

levels for two-way A N O V AA N O V As of species

richness and abundance of total fish,

flathead gudgeon, golden perch, common

carp and European perch by ‘Section’ and

‘Year’ for the Campaspe River between

October 1995 and February 2003

Source of

variation d.f.

Species

richness Total

Flathead

gudgeon

Golden

perch

Common

carp

European

perch

Section 2 14.250*** 0.841*** 1.178** 0.207 0.950** 0.845***

Year 6 2.067 0.038 0.407 0.103 0.426** 0.272**

Section · Year 12 1.264 0.103 0.141 0.131 0.145 0.147

Error 63 1.31 0.111 0.206 0.082 0.135 0.087

**P < 0.01, ***P < 0.001.



richness (middle, spring/summer). The fish variables

that were positively associated with low flow vari-

ables were total fish and YOY common carp (lower

section, in winter), YOY golden perch (upper, winter)

and European perch (middle, spring/summer). Total

fish (lower, winter) and flathead gudgeon (middle,

winter) were significantly associated with variability

in flows, the former positively, and the latter nega-

tively. YOY golden perch (lower, winter) and total fish

(lower, spring/summer) were positively related to the

threshold flow for the lower two weirs (23.15 m3 s)1),

whereas for YOY common carp, the relationship was

less clear; abundance of this group was positively

related to the number of spells over the 23.15 m3 s)1

and negatively related to the duration of these spells

and maximum flow in the lower section in spring/

summer.

Comparison of the Campaspe and Broken River

environments: 2000–2003

The Campaspe and Broken Rivers experienced

drought conditions for most of the period between

October 2000 and February 2003 (Figs 3a & 8a). The

only time when significant rainfall and runoff

occurred was during the spring of 2000, when mean

monthly discharge in the Broken River peaked at

approximately 28.94 m3 s)1 and in the Campaspe

River at approximately 11.57 m3 s)1.

Mean monthly water temperatures were generally

similar for the Campaspe and Broken Rivers, although

the latter reached marginally higher levels in mid-

summer and mid-winter than the former (Figs 3b &

8b). Conductivity was always lower in the Broken

River than the Campaspe River (Figs 3c & 8c). There

was a gradual rise in conductivity over the 3-year

study period in the Broken River, however, levels

never reached 400 lS cm)1, whereas they were rarely

below 400 lS cm)1 in the Campaspe River, even in the

upper section. Turbidity, on the other hand, was often

higher in the Broken River than the Campaspe River

(Figs 3d & 8d): the 3-year mean turbidity in the lower

and upper Broken River was 51.0 ± 5.1 and 34.3 ± 1.8

NTU, respectively, whereas in the lower and upper

Campaspe River it was 39.1 ± 4.0 NTU and 23.1 ± 4.6

NTU respectively. Turbidity levels, like conductivity,

showed an overall rise during the study period.

Dissolved oxygen concentrations were comparable

in the Broken and Campaspe Rivers during the 3-year

comparison, dropping to approximately 5 mg L)1 in

mid-summer and reaching approximately 10 mg L)1

in mid-winter (Figs 3e & 8e). As with pH levels in the

Campaspe River, those in the Broken River were

never lower than 7 and rarely greater than 8 (Figs 3f &

8f).

Comparison of the Campaspe and Broken River fish

faunas: 2000–2003

A total of three native and four alien species were

recorded from the Campaspe River and a total of five

native and four alien species were recorded from the

Broken River between August 2000 and February 2003

(b) Total fish

0

0.5

1.0

1.5

2.0

(e) Common carp

0

0.5

1.0

1.5

2.0

(d) Flathead gudgeon

0

0.5

1.0

1.5

2.0

(c) Golden perch

0

0.5

1.0

1.5

2.0

(f) European perch

0

0.5

1.0

1.5

2.0

1996 1997 1998 1999 2000 2001 2002

Lowersection

Middlesection Upper

section

Year

Abu

ndan

ce o

f fis

h

0123456

Fre

quen

cy(a) Species richness

Fig. 6 Mean + 1SE of (a) species richness and log10(x + 1)

abundance of (b) total fish, (c) golden perch, (d) flathead

gudgeon (e) common carp and (f) European perch for the lower

(black columns), middle (hatched) and upper (white) sections of

the Campaspe River between 1996 and 2002.



(Table 5). All together, 657 fish, comprising 56.6%

natives, were recorded from the Campaspe River and

a total of 398 fish, comprising 85.7% natives, were

recorded from the Broken River during this time. The

dominant species by number in the Campaspe River

was the flathead gudgeon, with common carp a close

second. The Broken River fish fauna was dominated

by golden perch, with common carp and carp

gudgeon species ranked approximately equal second.

Flathead gudgeon was never collected from the

Broken River, and Murray cod, river blackfish and

crimson-spotted rainbowfish were never collected

from the Campaspe River.

Almost twice the biomass of fish was collected in

the Broken River than the Campaspe River during the

3 years of study (Table 5). By weight, the Campaspe

River fish fauna comprised 28.5% native species,

whereas the Broken River comprised 49.6% native

species. Carp comprised approximately half of the

biomass, with golden perch ranked second, in each

river. Whilst European perch ranked third in biomass

in the Campaspe, Murray cod ranked third in the

Broken River.

The contribution of native species to the abundance

of all fish was highest in the middle section, interme-

diate in the upper section and lowest in the lower

section of the Campaspe River (Table 5). This pattern

can be explained almost entirely by the relatively

large number of carp collected from the lower section

and the relatively large abundance of golden perch

collected from the upper section of this river. The

contribution of native species to the lower section of

the Broken River was also the lowest of all sections,

but was intermediate in the middle and highest in the

upper section. Native species always comprised more

than 75% of the fish fauna in sections of this river. The

increasing percentage of native species from the lower

to upper section of the Broken River was a result of

(a) Common carp

(b) European perch (c) Golden perch

0

20

40

60

80

100

120

140

160

0

20

40

60

0

20

40

60

≥125 mm

<124 mm

01020304050

01020304050

01020304050

≥101 mm

<100 mm

010203040

010203040

010203040

≥201 mm

<200 mm

Lower

Middle

Upper

1995

/96

1996

/97

1997

/98

1998

/99

1999

/00

2000

/01

2001

/02

2002

/03

1995

/96

1996

/97

1997

/98

1998

/99

1999

/00

2000

/01

2001

/02

2002

/03

1995

/96

1996

/97

1997

/98

1998

/99

1999

/00

2000

/01

2001

/02

2002

/03

Spawning season

Abu

ndan

ce o

f fis

h

Fig. 7 Proportion of young-of-year (white bars) and older (black bars) (a) common carp, (b) European perch and (c) golden perch

collected in the Campaspe River between the 1995/96 and 2002/03 spawning seasons. YOY were defined as carp <124 mm (Brumley,

1996; Villizi & Walker, 1999), European perch <100 mm (Shafi & Maitland, 1971) and golden perch <200 mm (Anderson et al., 1992).



greater abundances of golden perch and carp gud-

geons.

Percentage biomass of native fish in the Campaspe

River did not show the same trends as abundance; in

this case the greatest percentage biomass of natives

was recorded in the lower section (Table 5). The

overall pattern was dominated by common carp and,

to a lesser degree, golden perch, because of their

large size. A greater biomass of carp was collected in

the upper section of the Campaspe River than in the

other two sections combined. The percentage of

native fish contributing to the biomass of fish in

the Broken River followed a similar trend, albeit

lower, than that of abundance: lowest in the lower

section and highest in the upper section. Again, carp

and golden perch contributed the most to patterns in

relative biomass.

Discussion

The Campaspe River fish fauna and its condition

The 10 native species recorded in the Campaspe River

between October 1995 and February 2003 is almost

certainly not a true reflection of the resident native

fish fauna in this river. Only four of the 10 species

were recorded consistently and in abundance over the

7 1/2-year study. Of these four, flathead gudgeon,

Australian smelt and the carp gudgeon complex are

small, short-lived species known to spawn and recruit

every year (Humphries et al., 2002). The remaining

species, golden perch, is a large, long-lived species,

but is stocked most years in the Campaspe River in

large numbers (Department of Primary Industries,

Victoria, unpubl. data). Furthermore, there was no

Table 4 Results of multiple regressions

on log10(x + 1) transformed fish (depen-

dent) and hydrological (independent)

variables for ‘winter’ and and ‘spring/

summer’ for the Campaspe River

Season Section Fish variable R2 Predictor vars Coefficients SE

Winter Lower Total fish 0.795* Intercept 1.343* 0.119

DSPELLLOW 0.390* 0.101

VAR 0.209* 0.075

Lower Golden perch 0.716** Intercept 0.702*** 0.105

DSPELLHIGH 0.554** 0.138

Lower YOY Golden

perch

0.642* Intercept 0.167 0.117

NSPELL23 2.230* 0.650

Lower European perch 0.622* Intercept 1.087*** 0.080

DSPELLHIGH 0.347* 0.022

Lower YOY common

carp

0.620* Intercept )1.341 0.694

NSPELLLOW 3.151* 0.960

Middle Flathead

gudgeon

0.815** Intercept 2.437*** 0.164

VAR )0.854** 0.163

Middle YOY European

perch

0.884** Intercept 0.755** 0.131

NSPELLLOW )0.477** 0.072

MED )0.241* 0.072

Upper YOY Golden

perch

0.743* Intercept )0.940* 0.304

NSPELLLOW 1.783** 0.417

Spr/sum Lower Total fish 0.624* Intercept 1.812*** 0.059

NSPELL23 0.577* 0.189

Lower YOY common

carp

1.000*** Intercept 3.839*** 0.062

NSPELL23 7.863*** 0.049

DSPELL23 )1.429*** 0.013

MAX )1.214*** 0.022

Middle Common carp 0.770* Intercept )0.585 0.354

MAX 0.450* 0.107

Middle Richness 0.728* Intercept 0.750*** 0.025

DSPELLHI )0.077* 0.020

Middle YOY European

perch

0.996** Intercept )0.5469** 0.218

MED 2.749*** 0.095

MIN )0.406* 0.044

DSPELLLOW 0.427* 0.050

R2 ¼ adjusted R2, for predictor variable definitions see Table 1.

* P < 0.05, ** P < 0.01, *** P < 0.001.



evidence that this species spawned during the entire

study period (Humphries et al., 2002; P. Humphries,

unpubl. data). The fact that there was no effect of

section on the abundance of golden perch, whereas

there was for all other non-stocked dominant species,

suggests, perhaps, that regular stocking is maintain-

5

6

7

8

9

O D F J O D F J O D F

0

50

100

150

0

100

200

300

400

50005

1015202530

2000 2001 2002 2003

(f)

(e)

(d)

(c)

(b)

(a)

pHD

isso

lved

oxy

gen

(mg

L–1)

Tur

bidi

ty (

NT

U)

Con

duct

ivity

(µS

cm

–1)

Tem

pera

ture

(°C

)Dis

char

ge (

m3 s

–1)

0

5

10

15

Date

05

101520253035

Fig. 8 Discharge, temperature, conductivity, turbidity, dissolved oxygen and pH measurements taken for the upper (dotted line),

middle (dashed) and lower (solid) sections of the Broken River between October 2000 and February 2003. Note: discharge is presented

for the upper section (dotted line) and the middle and lower sections combined (solid line) of the Broken River, because of where the

river is gauged.



Tab

le5

Per

cen

tag

eab

un

dan

cean

db

iom

ass,

tota

lab

un

dan

cean

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ing this species throughout the river as a whole.

Considering that approximately 18–20 of the 34

Murray-Darling Basin native fish species probably

once inhabited this river (Humphries & Lake, 2000),

the extant native fish fauna of the Campaspe River is

thus extremely poor. Historically, this river was

known for its abundant Macquarie perch and Murray

cod populations (Anonymous, 1973; Langtry in

Cadwallader, 1977), but it is now virtually unheard-of

for the former, and uncommon for the latter, to be

caught by anglers.

A total of six alien species was recorded during the

study, and those collected consistently are also the

most common alien species encountered in south-

eastern Australia (Cadwallader, 1978; Arthington &

Mitchell, 1986; Koehn, 2002, 2004; Kennard et al.,

2005). Common carp and European perch comprised

approximately 64% of the biomass and 36% of the

abundance of fish collected overall; a figure compa-

rable to studies elsewhere in Australia where these

species occur (Gehrke et al., 1995).

Our results indicated that there were substantial

differences in the fish fauna of each of the hydro-

logically-distinct sections of the Campaspe River and

broadly confirm our predictions related to the degree

of flow alteration and richness and dominance of

native and alien species. Thus, species richness of

natives was greatest in the lower section, lowest in

the upper section and intermediate in the middle

section. These differences were a result of the

presence of carp gudgeons, Murray cod, Australian

smelt, silver perch and flatheaded galaxias in the

lower and middle section, but not in the upper

section. Parallel work on larval fish, using methods

more suitable for capturing Australian smelt, indi-

cated that this pelagic, shoaling species was as

abundant in the upper section of the river as it was

in the other two sections (Humphries et al., 2002). On

the other hand, from the results presented here and

from observations over many years, we believe that

the absence of the other species from samples in the

upper Campaspe is a true reflection of their absence

or rarity in that section (Humphries et al., 2002;

P. Humphries, unpubl. data). Alien species tended to

be more extensive in their spatial distribution in the

Campaspe River than did native species. Common

carp, European perch and goldfish occurred in each

section, albeit in decreasing abundance with increas-

ing distance upstream.

Fish fauna and hydrology

There are few studies in Australia or the rest of the

world where changes to the fish fauna of a river can

be attributed directly to flow alteration (Lloyd et al.,

2003; Lytle & Poff, 2003). The main reason for this is

because of the impracticality of conducting rigorously

designed – controlled and replicated – experiments in

anything but the smallest systems. Nevertheless, we

can gain substantial insight into the influence of flow

by comparisons across broad geographic areas in

streams which differ in their flow regimes and

associated characteristics (Lamouroux & Cattaneo,

2006). Similarly, in our study we have been able to

compare characteristics of the fish fauna of the

Campaspe River among three river sections that

experience contrasting hydrologies. We have also

been able to describe relationships between fish-

related variables and hydrological variables and to

contrast the Campaspe River and the similar, but less

regulated Broken River. An important point to note,

however, is that much of the study reported here

occurred during an extended dry period and that the

patterns observed were without doubt a function of

both natural climatic and anthropogenic influences.

Our analysis of the fish fauna during the 7 1/2 -year

study indicated that the lower section of the Campa-

spe River was consistently the most species rich; again

confirming our prediction that the greater degree of

regulation the fewer native species occurring, since

this section was the least regulated of the three. When

access to the Campaspe River from the Murray River

is possible, this means that this section will potentially

be more accessible than at least the upper section.

These patterns in species richness by section were,

however, not reflected in relationships between

threshold discharge levels for upstream movement

over weirs and species richness in the lower section,

although species richness was positively related to

high flow variables in the middle section of the river.

Thus, our prediction that fish-related variables, such

as richness, would respond to high or threshold flows

was not confirmed. The general lack of significant

relationships between hydrology and richness is not

entirely surprising, given the rarity of the upstream

connection between the Murray River and the lower

Campaspe and between the lower and middle Cam-

paspe (about a month in total in 1996 and for 3–4 days

in 2000) and between the middle and upper sections



(2–3 days in 1996) and because of the relatively small

pool of species in the river.

Irrespective of the potential for movement between

river sections, greater species richness in the lower

Campaspe River is consistent with the widely held

view of a positive relationship between species rich-

ness and stream order (see Matthews, 1986). How-

ever, what fish are responding to is the subject of

ongoing debate; it may relate to diversity of habitat

(Gorman & Karr, 1978), rates of immigration and

emigration (Power et al., 1988) or drainage basin size

or stream length, width or gradient (Lake, 1982;

Grenouillet, Pont & Herisse, 2004). In contrast to the

Campaspe River, despite the presence of two sub-

stantial weirs, there was no decline in number of

species evident with increasing distance upstream in

the Broken River. Indeed, our prediction that there

would be more native species, and that they would

comprise a larger proportion of the fish fauna in the

Broken than in the Campaspe River, was confirmed. It

is thus unlikely that the decline in species with

distance upstream from the Murray River confluence

can be explained solely by the presence of weirs in the

Campaspe River. We have little doubt, however, that

there will be some species, especially those thought to

move considerable distance as part of their normal life

history (Reynolds, 1983; Koehn, 1997; Koehn & Nicol,

1998; Koehn, Stuart & Crook, 2003), which will not be

in abundance above barriers without regular stocking.

The high degree of regulation in the upper section

of the Campaspe River has been proposed by

Humphries et al. (2002) as having a deleterious effect

on the fish fauna of this system. Differences in

physico-chemical variables between the Campaspe

and Broken Rivers, mainly turbidity and conductivity,

and between the upper and the middle and lower

sections of the Campaspe River, seem unable to

explain the differences observed. In addition, temper-

ature depression, as a result of low-level releases from

Lake Eppalock, is relatively minor and inconsistent,

compared with other systems, like the Goulburn and

Murray Rivers (McMahon & Finlayson, 1995), and is

also unlikely to explain the observed differences. As

circumstantial evidence for the impacts of flow alter-

ation, Humphries et al. (2002) cited the absence of carp

gudgeons, a species considered vulnerable to river

regulation (Gehrke, 1997), in the upper section of the

Campaspe River, the dominance of small, opportu-

nistic, short-lived native species which breed over a

protracted period and the success of generalist alien

species. These authors proposed that the enhanced

flows over the spring/summer period in the upper

section of the Campaspe did not prevent spawning for

most species but reduced the area of slackwater

rearing habitats. Recent experiments in a lowland

river, in which slackwaters were ‘destroyed’, through

diverting current into existing slackwater patches,

showed that simulating the effects of irrigation flows

displaced larvae from slackwaters (Humphries et al.,

2006). River regulation has also been shown generally

to affect recruitment in other rivers systems in the

world (Robinson, Clarkson & Forrest, 1998; Liebig

et al., 1999; Merigoux & Ponton, 1999; Schiemer et al.,

2001).

The Campaspe River’s fish fauna is, however,

depauperate throughout its length downstream of

Lake Eppalock; not just in the upper section, where

most of the irrigation releases occur. It is logical,

especially for highly mobile organisms such as fish,

and for rivers that are longitudinally connected, that

the effects of flow alteration on fish faunas will extend

beyond the immediate area that is heavily regulated.

Some clues to how flow affects this river’s fish fauna

may, perhaps, be gained from sporadic recordings of

species during our study and how they relate to flow

conditions. The only major high flow event which

occurred during the 7 1/2-year study was in the

winter/spring of 1996, although a brief period of

relatively high flow also occurred in late 2000. For

several weeks between August and October of 1996,

Lake Eppalock spilled, the river was very high and

filled billabongs and anabranches and broke its banks

in places, and this was the same time during which

we estimate that threshold levels of discharge were

reached sufficient for fish to move into both the lower

and middle sections of the river and, possibly, for 2–

3 days into the upper from the middle section.

Downstream movement, even from above Lake Ep-

palock, was possible during these high flow events.

During that time, or in the months following the high

flow period, several species were collected that had

not been recorded prior to this, which were mostly not

recorded for the rest of the study and which

responded to high flow events by moving consider-

able distances upstream or downstream. Therefore,

there is qualitative evidence that our prediction that

fish will respond to high or threshold flows through

movement over weirs may have some validity. Under



unregulated conditions, only small rises in flow

would have allowed unimpeded movement through-

out much of the length of the Campaspe River. Since

Lake Eppalock was built, however, movement be-

tween river sections would be limited predominantly

to when the storage filled and spilled; prior to 1996,

approximately every 2 years, but since that time,

never.

Despite the likely effect of high flow events on fish

movement, there was no quantitative relationship

between the overall composition of the Campaspe

River fish fauna and any hydrological variables,

which is contrary to our predictions. This was some-

what unexpected, considering the large inter-annual

differences in discharge during the study. Thus, the

composition was stable over a period, which in-

cluded, as stated above, a high flow year, a moderate

flow year and 5 years when flows were very low.

However, again, there is a relatively small suite of

species which is driving the overall composition, and

these are species – both native and alien – are known

to have broad habitat and water quality tolerances

and life histories which allow them to breed and

recruit under a range of conditions (Humphries et al.,

2002). There has been much effort expended on the

question of how stable fish assemblages are and the

mechanisms behind their variability (see e.g.

Grossman, 1982; Matthews, Cashner & Gelwick,

1988; Schlosser & Ebel, 1989; Grossman, Dowd &

Crawford, 1990; Poff & Allan, 1995; Grossman et al.,

1998). There seems to be general agreement, however,

that flow variability - high flows in general (and short

spates in particular) – affect fish assemblage variabil-

ity (Oberdorff et al., 2001; Schiemer et al., 2001; Koel &

Sparks, 2002; Li & Gelwick, 2005), although this

agreement is not universal (see e.g. Moyle & Vond-

racek, 1985). It appears that the nature of the differ-

ences among the three river sections of the Campaspe

and the nature of the species which remain in this

degraded system outweigh any among-year differ-

ences in their influence on characteristics of the fish

fauna.

When the abundances of individual species and life

stages were examined, however, several were signif-

icantly related to hydrological variables. For example,

the abundance of golden perch in winter in the lower

section was positively related to the duration of 10th

percentile flows and above, suggesting the potential

for movement upstream from the Murray River in

response to high flows. Total fish abundance in the

lower section in winter, on the other hand, was

positively related to the duration of 90th percentile

flows and a measure of variability in flow. The reason

for this is uncertain. Indeed, it is hard to come to

general conclusions regarding fish/hydrology rela-

tionships for the fish fauna, the river and hydrological

seasons. This could be due to the fact that the duration

of the study was still too short for robust investigation

of relationships, the fact that each section of river has

a distinct hydrology and therefore is probably oper-

ating differently and so we would expect relation-

ships between hydrology and fish to be different

among river sections, or that these types of rivers have

high inter-annual variability in flow and antecedent

conditions, perhaps extending for many years, play a

role in the abundances that we see in any one year.

An example, perhaps, of the complexities of fish/

hydrology relationships is of the recruitment of

common carp. Abundance of YOY carp showed two

peaks: a minor one in 1996/97, during a year of high

rainfall, high flows and extended periods of connec-

tion for the river system below Lake Eppalock and a

major one in 2000/01, when rainfall and flows were

much higher than in the last 3 years, but considerably

lower than in 1996. This resulted in the apparently

contradictory positive relationship between YOY carp

abundance and the number of spells of 90th percentile

flows in the lower section of the river. But this is

explainable by the fact that it was the 1996/97 and

2000/01 years which influenced the significance of the

relationship, and that in these two recruitment years,

YOY carp abundance was lowest during the higher of

the two flows and highest during the lower of the two.

Strong carp recruitment was also reported in major

floodplain wetlands of the Murray River in the 2000/

01 breeding season, in response to an environmental

water release (Brown et al., 2005; Crook & Gillanders,

2006). Indeed, this species seems to respond to

inundation of previously dry habitat by spawning in

many locations in the Murray-Darling Basin (King,

Humphries & Lake, 2003; Smith & Walker, 2004;

Driver et al., 2005).

In conclusion, we have found evidence that the

differences that exist in the fish fauna of the three

sections of the Campaspe River are likely to be due to

differences in hydrology and that the fish fauna of

this river as a whole is in a poorer state than the less

regulated Broken River. This adds weight to the call



for more sensitive management of rivers, especially

for rivers which are heavily regulated and which

have for decades been managed solely as irrigation

conduits. Providing periodic moderate-to-high flows

and threshold flows over barriers or – better still –

allowing fish passage through fishways or removal of

weirs altogether will mean that fish will be able to

move into and out or areas for life history purposes,

for the acquisition of food, to recolonize river sections

and to escape potentially harmful conditions, such as

blackwater events. Despite some progress in under-

standing, our 7 1/2-year study is apparently still of

insufficient duration for proper investigation of fish/

hydrology relationships. It is sobering to realize that

for this to be accomplished, riverine fish studies of

20+ years are probably needed. These are rare in the

world (although see e.g. Daufresne et al., 2003) and

entirely absent in Australia. With the likelihood of

reduced streamflows in south-eastern Australia and

increased temperatures associated with climate

change, it is all the more imperative that long-term

studies are initiated now in order to understand the

link between fish and flow and to make predictions

for the future.

Acknowledgments

We would like to thank the researchers who assisted

in various aspects of the field and laboratory work

associated with this study; especially David Crook,

Alison King, Jane Growns, Simon Lukies, Zeb Tonkin

and Helen Gigney. Rob Cook and Adam Richardson

were a constant source of critical comment and bad

jokes and Nicole McCasker provided helpful com-

ments on the manuscript. Sam Lake, Gerry Quinn,

Terry Hillman, Ben Gawne, Peter E. Davies, Angela

Arthington and John Harris provided support and

guidance, intellectually and administratively. Peter

Cullen and Barry Hart were, amongst others, instru-

mental in helping to get the project going and to keep

it going beyond the normal 3 years. Many landowners

on the Campaspe and Broken Rivers gave up their

valuable time to provide information and advice, as

well as much appreciated hospitality. We would

especially like to thank the Danahers and the Keats

for their consistent congeniality, tolerance and story-

telling. This study was funded jointly by the Cooper-

ative Research Centre for Freshwater Ecology, the

Commonwealth Department of Environment and

Heritage (through Environment Australia and Land

and Water Australia) and Goulburn-Murray Water.

Thiess Environmental Services kindly supplied

hydrological data and the Goulburn-Broken Catch-

ment Management Authority assisted in many ways.

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Documents

APPLIED ISSUES Flow-related patterns in abundance and composition