effects of flow on lateral interactions of fish and shrimps with off
TRANSCRIPT
WORLD’S LARGE RIVERS CONFERENCE
Effects of flow on lateral interactions of fish and shrimpswith off-channel habitats in a large river-floodplain system
K. Gorski • K. J. Collier • D. P. Hamilton •
B. J. Hicks
Received: 31 January 2012 / Accepted: 3 October 2012 / Published online: 4 December 2012
� Springer Science+Business Media Dordrecht 2012
Abstract Off-channel habitats play a crucial role in
the life-cycles of many riverine fish species, but lateral
movements of fish into these habitats are poorly
understood. We tested how flow dynamics affects the
movement of fish and shrimps between the main river
channel and different types of off-channel habitats: a
riverine lake and a wetland. Our study site was the
lower Waikato River, North Island, New Zealand,
where there are numerous off-channel habitats. Fish
were sampled using directional fyke nets. Shortfin eel
(Anguilla australis) migrated mostly into the wetland
at night, particularly during high river flows. Common
bullies (Gobiomorphus cotidianus) were most abun-
dant during the day and in low-discharge conditions,
moving mostly into the riverine lake, whereas fresh-
water shrimp (Paratya curvirostris) moved mostly
into the wetland. High numbers of non-native larval
common carp (Cyprinus carpio) moved out of the
wetland with retreating flood water. This study
emphasises the importance of lateral connectivity
and flooding in functioning of this river system where
numerous native fish, but also exotic fish, used off-
channel habitats. Floodplain management strategies
should promote ‘controlled connectivity’ measures
that provide access for native species at key times
while limiting opportunities for introduced species to
utilise their favoured off-channel habitats.
Keywords Fish movement � Habitat connectivity �Floodplain � Riverine lake �Wetland �Waikato River
Introduction
Floodplain wetlands adjoining large lowland rivers are
amongst the most biologically productive freshwater
ecosystems (Tockner et al., 2009). Seasonal flow and
flood pulses increase connectivity between various
components of riverine systems, expanding habitat
availability for aquatic organisms (Junk et al., 1989;
Tockner et al., 2000). Currently, large river–floodplain
systems that retain a high degree of natural function-
ality are rare in temperate regions, and most are highly
modified by river regulation, e.g. construction of dams
and dykes, changes in land use, and introductions
of non-native species (Bayley, 1995; Tockner &
Stanford, 2002; Nilsson et al., 2005). Off-channel
Guest editors: H. Habersack, S. Muhar & H. Waidbacher /
Impact of human activities on biodiversity of large rivers
K. Gorski (&) � K. J. Collier � D. P. Hamilton �B. J. Hicks
Environmental Research Institute—Te Putahi Rangahau
Taiao, University of Waikato, P. O. Box 3105, Hamilton,
New Zealand
e-mail: [email protected]
K. J. Collier
Waikato Regional Council, P. O. Box 4010, Hamilton,
New Zealand
123
Hydrobiologia (2014) 729:161–174
DOI 10.1007/s10750-012-1352-1
habitats such as floodplain wetlands and lakes can be
crucial in supporting feeding, spawning and nursery
areas for many riverine fish species (Junk et al., 1989;
Baber et al., 2002; King et al., 2003; Jimenez-Segura
et al., 2010; Gorski et al., 2011a; Magana, 2012).
Consequently, in many river systems, fish community
structure and production are directly related to the
quality and quantity of connections between main
river channels and off-channel floodplain habitats
(Welcomme, 1979; Moses, 1987; De Graaf, 2003;
Gorski et al., 2011b).
In European rivers, cyprinids have been shown to
migrate from the main river channel into off-channel
habitats, including tributaries (Nunn et al., 2010),
floodplain water bodies (Molls, 1999; Hohausova
et al., 2003) and temporarily inundated grasslands
(Cucherousset et al., 2007), especially with increas-
ing river discharge and during floods. Similar
phenomena have been observed in large tropical
rivers with highly predictable seasonal floods, where
the lateral migration of fish closely followed the
dynamic ‘pulsing’ of water levels (Junk et al., 1989),
enabling fish to access superior feeding and nursery
habitats as water levels rose and advanced over
terrestrial riparian habitats during seasonal floods
(Wantzen et al., 2002; Castello, 2008). In the North
American temperate Kankakee River, for example,
fish species adapted to seasonal flooding have been
shown to repeatedly seek out floodplain habitats
during high flows, whilst being forced to the main
channel during low flows (Kwak, 1988). The
importance of off-channel habitats during low flow
conditions has been stressed in recent studies from
the Murray Darling Basin in Australia, where high
numbers of both native and non-native fish moved to
accessible off-channel habitats during low water
levels (Lyon et al., 2010; Conallin et al., 2011).
During winter, when low water temperatures limit
metabolism and swimming performance, many tem-
perate fish species prefer lentic backwater conditions
to conserve energy (Lucas & Baras, 2001). Off-
channel habitats can also provide refuges for fish from
high water velocities during high flows (Schwartz &
Herricks, 2005), and allow fish to restore energy
reserves after spawning (Fernandes, 1997; Gorski
et al., 2010). However, organically enriched backwa-
ter and floodplain habitats may often suffer hypoxia,
forcing fish to move back to flowing water of the main
river channel (Knights et al., 1995).
To make informed decisions about the rehabilita-
tion of riverine fish production, it is essential to
understand the ecological role of off-channel habitats
for both native and introduced species (Galat et al.,
1998; Buijse et al., 2002). Compared to large-scale
longitudinal migrations within river corridors, how-
ever, lateral fish movement and migrations in lowland
rivers remain one of the most poorly understood
dispersal mechanisms in temperate freshwater eco-
systems (Lucas & Baras, 2001; Nunn et al., 2010).
This is particularly so in New Zealand and other
southern hemisphere temperate countries where the
native fish fauna is dominated by diadromous species
(McDowall, 1990), and studies on lateral movement
are scarce.
The Waikato River is New Zealand’s longest river.
Its lower reaches were historically characterised by
extensive river–floodplain interactions (Collier et al.,
2010a), and the river once supported the most
productive whitebait (Galaxias spp.) and eel (Anguilla
spp.) fisheries in New Zealand (Stancliff et al., 1988;
Chapman, 1996). Complex riverine habitats associ-
ated with floodplain wetlands and riverine lakes
provided important habitat for a range of species in
the Waikato River, including many native fish that are
now considered to be endangered (Collier et al.,
2010b). Before European settlement, floodplain areas
in the lower Waikato River extended to around
364 km2, but at present only about 53% of that area
remains due to implementation of flood protection
schemes and changes in land-use (Collier et al.,
2010a). Twelve introduced fish species now co-occur
with native species, with common carp Cyprinus
carpio (Linnaeus, 1758) often dominating fish bio-
mass in the lower river (Hicks et al., 2010).
In this study, we investigated movement of larval
and juvenile fish between the main river channel and
two types of lateral habitats (riverine lake and
floodplain wetland) in the lower Waikato River. Our
specific objectives were to: (1) quantify the abundance
of fish moving into and out of a riverine-lake and
wetland habitats in different seasons compared to
movements within the main river channel, and (2)
investigate the role of selected environmental cues
associated with movement into and out of off-channel
habitats for different fish species. We hypothesised
that seasonal variations in flow could play a crucial
role in triggering lateral movement of both native and
introduced fish from the Waikato River into off-
162 Hydrobiologia (2014) 729:161–174
123
channel habitats (Hohausova et al., 2003; Nunn et al.,
2010). We further hypothesised that high flows could
trigger movement of fish, so that shortfin eel, Anguilla
australis (Richardson, 1841), might exploit off-chan-
nel habitats for feeding as well as exposed floodplain
areas with retreating water, as shown for Anguill
anguilla (Linnaeus, 1758) in Europe (Lasne et al.,
2008). Small-bodied fish species such as ınanga
Galaxias maculatus (Jenyns, 1842) as well as fresh-
water shrimps Paratya curvirostris (Heller, 1862)
might be expected to move into the off-channel
habitats to avoid high water velocities in the main
channel during floods (Schwartz & Herricks, 2005).
Methods
Study area
The Waikato River flows in a northerly direction for
around 442 km from its headwaters above Lake Taupo
to the Tasman Sea at Port Waikato (Collier et al.,
2010b). It drains a total catchment of 14,443 km2 and
has a mean annual discharge at the mouth of approx-
imately 450 m3 s-1 (Brown, 2010). The catchment
has been significantly altered from its natural state,
mostly for agriculture (62%) and exotic forestry
(19%), as well as some urban development (Collier
et al., 2010b), whilst the upper river is punctuated by
eight hydro dams. A dam 152 km upstream from the
river mouth effectively acts as a barrier to the natural
upstream movement of aquatic fauna. Soils in the
Waikato River catchment are dominated by sediments
with low infiltration rates, and therefore the river
system is highly responsive to rainfall, with large peak
flood flows after heavy rain (usually in winter and
spring) and low flows after periods of low rainfall
(summer and autumn) (Brown, 2010).
This study was conducted in the Waikato River’s
lower reaches, where it forms a low-gradient river
accommodating extensive floodplains which are char-
acterised by peat wetlands and several riverine lakes,
although these interactions are now highly regulated
by a flood protection scheme which was initiated in
the 1950 and 1960s (Chapman, 1996). Lake Whangape
(‘Lake’) and Opuatia wetland (‘Wetland’) were
selected as off-channel habitats to quantify fish move-
ment to and from the river main channel at different
discharges (Fig. 1). These habitats are amongst the few
remaining which have relatively undisturbed connec-
tivity with the river main channel in the lower Waikato.
Lake Whangape has a surface area of 14.5 km2 and
muddy sediments, and is a turbid, hyper-eutrophic lake
with high productivity dominated by phytoplankton;
aquatic macrophytes are absent (Hamilton et al., 2010).
A stone weir constructed in the lake for water level
control limits connectivity with the river main channel
in low flows, but during moderate to high flows the weir
is fully submerged, allowing unrestricted fish move-
ment. Opuatia wetland covers approximately 9.5 km2
and is one of the few remaining wetlands retaining
dominance of native restiad rushes (Clarkson et al.,
2004), supported by a peat bog surrounded by minera-
lised margins (Beard, 2010). Water originating from
the peat bog may periodically induce hypoxia in the
outflow of the wetland (Kuder & Kruge, 2001). Some
flood protection works have been carried out in this
wetland, including construction of bunds along the
boundaries of willow and pasture areas (Beard, 2010).
Fig. 1 The study area indicating sampling sites (circled fish)
and its location in New Zealand
Hydrobiologia (2014) 729:161–174 163
123
Data collection
Water level and temperature were recorded at 1-h
intervals at the inlet to each off-channel habitat using
automatic data loggers (3001 Levelogger� Junior;
Solinst Canada, Ontario, Canada). Daily discharge data
of the Waikato River at Rangiriri (approximately 5 km
upstream from the main channel sampling site (Fig. 1);
37�25055.8800S, 175�7041.5000E) were obtained for the
sampling period from Waikato Regional Council,
Hamilton, New Zealand. In addition, spot water
temperature, dissolved oxygen and specific conduc-
tance were recorded approximately 1 m below the
water surface on each sampling occasion using hand-
held devices (YSI model 55 handheld DO meter and
YSI 30 meter; Yellow Springs Instruments, OH, USA)
for conductance and temperature, respectively.
Fish were sampled bi-monthly between 29 September
2010 and 16 September 2011 to encompass seasonal
variations and different water levels and flows. Sam-
pling was conducted at the Lake Whangape inlet
(37�25050.7900S, 175�4042.9000E), which was character-
ised by water depth 1–2 m, width c. 30 m in low flow
conditions, muddy sediment and aquatic macrophytes
absent, and at Opuatia wetland inlet (37�24037.5000S,
175�3028.5500E), where thedepth was 1–2 m, the width c.
20 m in low flow conditions, muddy sediment and about
10% areal coverage with aquatic macrophytes (mostly
hornwort Ceratophyllum demersum L.) (Fig. 1).
To compare movement patterns into and out
of the lake and wetland with those in the main channel
during each sampling, fish were also collected from
the shore of a mid-channel island (37�2500.1600S,
175�4015.1600E; Fig. 1), where the depth was 1–2 m
and sediments were sandy, while aquatic macrophytes
absent. On each sampling occasion, a set of two-
directional double-wing fyke nets (2.5 m wing span)
was set in each location over the same 24-h period. As
this study concentrated on small and juvenile fish, fine-
mesh (2 mm) nets were used. The nets were set at
similar depths in each location, facing both upstream
(‘in’) and downstream (‘out’) to catch fish moving ‘in’
and ‘out’ of the off-channel habitats. Nets were
checked close to dawn and dusk to give an indication
of diurnal movement patterns. For each sample, fish
were identified to species-level based on morpholog-
ical features and pigmentation (Koblitskaya, 1981;
McDowall, 1990). Fish were measured for total length
(±1 mm) for at least 100 individuals if available to
derive length–frequency distributions. For the less
abundant fish, all individuals were measured. Catch per
unit effort (CPUE) was calculated for day and night
samples, expressed as number of fish caught per hour.
Data analysis
We used permutational multivariate analysis of variance
(PERMANOVA) (Anderson, 2001; McArdle & Ander-
son, 2001) to determine differences in CPUE between
the main channel and off-channel habitats for different
species. This test was chosen because we wished to
assess the differences between habitats and seasonal
dynamics as well as their interactions, and CPUE data
did not meet normality assumptions for parametric tests.
PERMANOVA provides analysis of the variance of
data for a set of explanatory factors on the basis of
dissimilarity measures, thereby allowing a wide range of
empirical data distributions. Models were run based on a
Bray–Curtis dissimilarity matrix for the whole fish
community, and separately for the four most abundant
native fish species and freshwater shrimp based on
similarity among dates and sites. Data were square root-
transformed prior to analysis to reduce the effect of
outliers. For the two most abundant species—the
common bully Gobiomorphus cotidianus (McDowall,
1975) and shortfin eel—we compared size distributions
of individuals between habitats and directions of
movement using a Kolmogorov–Smirnov test.
Finally, to identify the relationship between move-
ment patterns and habitat type, flow magnitude, water
temperature and measured water quality variables
(dissolved oxygen concentration and conductance),
we performed redundancy analyses (RDA) (based on
correlation matrices) (Jongman et al., 1995; ter Braak
& Smilauer, 2002) on square root-transformed CPUE
data of the five most abundant species fish moving into
or out of off-channel habitats (river samples were
excluded). Global Monte Carlo permutation tests
(1,000 permutations) were performed to determine
the significance of the ordination at a = 0.05.
Results
Flow and water quality parameters
The river flow during the sampling period was
characterised by high discharge in spring 2010
164 Hydrobiologia (2014) 729:161–174
123
(September–October) and winter 2011 (May–August),
with a short (1-week) flood peak in summer (February
2011) (Fig. 2, top panels). Water temperature was
highest in the lake inlet and the lowest in the wetland
inlet (Table 1) over the period of sampling. During
spring flooding, water temperature gradually
increased in both the lake and the wetland, and
reached 20–24�C during the summer months (Janu-
ary–February), gradually decreasing during winter
high flows (Fig. 2, top panels). Daily fluctuations in
water temperature were about threefold larger at the
lake inlet compared to the wetland inlet (Fig. 2, top
panels). On average, during the sampling period,
oxygen saturation was high in the lake inlet (*102%)
and main channel (*92%) and low in the wetland
inlet (*38%), whereas specific conductance was
higher in both lake and wetland inlets (191 and
206 lS cm-1, respectively) compared to the main
channel (148 lS cm-1) (Table 1).
Fish movement patterns
During the entire period of sampling, we caught a total
of 2,856 fish and 1,834 freshwater shrimp (Table 2).
Highest numbers of fish were captured at the inlet to
the lake (1,506) with about half the number in the
wetland (837) and fewer in the main channel (513).
Freshwater shrimp were most abundant at the inlet to
the wetland (1,029), followed by the main channel
(539) and lake (266). The majority of fish species, as
well as the freshwater shrimp, moved in both direc-
tions at all sampling locations, but the overall direction
of movement varied between different habitats.
Overall, the majority of fish moved downstream in
the main channel (77%) or into the lake (69%),
whereas for the wetland, similar numbers of fish
moved in both directions.
The frequency and direction of fish movements
varied both temporally (on both diel and seasonal
scales) and between different off-channel habitats.
Comparisons were made of abundance over time
between the different habitats and directions of
movement for the four most abundant native fish
species, as well as the abundant freshwater shrimp
(Fig. 2). Similar sampling depths and method allowed
abundance comparisons between different sites and
indicated species-specific behaviours. The movements
of shortfin eels were mostly nocturnal, whereas
ınanga, common bully and common smelt moved
mostly during the day (Fig. 2). In contrast, the
freshwater shrimp showed less diurnal variation in
directional movement, with similar numbers during
both day and night. High river discharge in spring
triggered movement of shortfin eel into the off-
channel habitats at night, with numbers of eels moving
into the wetland about fivefold higher than those
moving into the lake (Fig. 2; Table 3). In contrast,
common bullies were most abundant during low
discharge in summer and at the river inflow into the
lake, moving in both directions but with more than
70% moving into the lake (Fig. 2; Table 3). Inanga
moved into both the lake and wetland in similar
numbers, and their abundances at the inlets were about
twofold higher than in the main channel. Common
smelt was most abundant in the main channel. We
observed about twofold higher abundances of fresh-
water shrimp in the wetland compared to the main
channel, with significantly more individuals moving
out of the wetland after high flows (Fig. 2; Table 3).
Abundances of freshwater shrimp in the inlet to the
lake were lower than those of the main channel.
We also observed significant numbers of intro-
duced fish species at inlets to both off-channel
habitats. Gambusia was the third most abundant
species in the lake inlet (after native common bully
and shortfin eel), and moved in both directions. It was
also present at the other locations, but in very low
numbers (Table 2). We recorded numerous larvae of
non-native common carp moving out of the wetland
(Table 2). One individual each of brown bullhead
catfish and rudd was caught moving out of the wetland
(Table 2). There were no differences in size distribu-
tion of shortfin eel between habitats (Fig. 3), but we
found some indication of slightly higher numbers of
smaller common bully moving into the lake compared
with moving out of the lake (Fig. 3; Table 2), although
these differences were not statistically significant.
Results of the redundancy analyses showed that
habitat type, flow, water temperature, dissolved oxy-
gen and specific conductance explained much of the
variation in the abundance of fish moving in both
directions (51 and 59% for fish moving into and out
of the off-channel habitats, respectively; Table 4). We
observed consistent patterns in species—environment
associations for some common species (Fig. 4).
Common bully and gambusia were positively associ-
ated with lake habitat, higher dissolved oxygen
concentration and higher water temperature (summer
Hydrobiologia (2014) 729:161–174 165
123
Main channel
0
6
6
12
12
6
12
6
12
Lake
0
6
12
Wetland
0
6
12Anguilla australis
0
2
2 2 2
0
2
0
2
Galaxias maculatus
CP
UE
(n
o h
-1)
0
20
20
40
40
20
40
20
40
0
20
40
0
20
40
Gobiomorphus cotidianus
0
2
2
4
4
2
4
2
4
0
2
4
0
2
4
Retropinna retropinna
Oct Dec Feb Apr Jun Aug
0
10
10
20
20
10
20
10
20
Oct Dec Feb Apr Jun Aug
0
10
20
NightDay
Oct Dec Feb Apr Jun Aug
0
10
20
Paratya curvirostris
6
12
18
24
30
Wat
er le
vel (
m)
1
2
3
4
5
Daily water temperature (mean ± range)Daily discharge / Relative water level
Tem
per
atu
re (
°C)
6
12
18
24
30
1
2
3
4
5D
aily
dis
char
ge
(m3 s
1 )
0
400
800
1200
In
Out
In
Out
In
Out
In
Out
In
Out
In
Out
In
Out
In
Out
In
Out
In
Out
In
Out
In
Out
In
Out
In
Out
In
Out
-
Fig. 2 Waikato River discharge at Rangiriri, and water level
and temperature at Lake Whangape and Opuatia wetland
between September 2010 and September 2011 (top). Movement
dynamics of fish and freshwater shrimp (bottom) in the main
channel as well as at inlets to Lake Whangape and Opuatia
wetland between September 2010 and September 2011
166 Hydrobiologia (2014) 729:161–174
123
season) for both ‘in’ and ‘out’ movements. In contrast,
shortfin eel and common smelt moved mostly into the
wetland, especially with higher flows and lower water
temperatures (spring). Common carp moved mostly
out of the wetland habitat, mostly with higher flows
(spring).
Discussion
We observed significant numbers of fish moving to
and from both the riverine lake and wetland habitats
investigated in this southern hemisphere large river,
supporting the conclusion that lateral connectivity
between the main river channel and off-channel
habitats is a key feature of ecological integrity in
riverine ecosystems (Copp, 1989; Junk et al., 1989;
Hohausova et al., 2003). Moreover, the present study
highlights the importance of different off-channel
habitats (i.e. lakes, wetlands) for fish productivity as
different native species varied in their use of riverine,
lake or wetland habitats. In this study, we refer to
the exchange of biota between the main river channel
and off-channel habitats as ‘movements’ rather than
‘migrations’, defined as synchronised movements that
are large relative to the average home range for a
species and occur at specific stages of the life-cycle
(Lucas & Baras, 2001). Although it is possible that
some species interact with off-channel habitats during
migrations, most of the movements in the present
study likely occurred over a small scale in response to
environmental factors associated with inundation of
lateral habitats.
Flow triggers the movement of native fish
Movements of shortfin eels and ınanga into the
wetland were driven mostly by changes in river
discharge, especially spring floods, supporting our
hypothesis that seasonal variations in flow can play a
crucial role in triggering lateral movement of fish.
Similar behaviour has been observed in Europe for
cyprinids, which move from the main river channel
into tributary (Nunn et al., 2010) or floodplain (Grift
et al., 2001; Hohausova et al., 2003) habitats at high
flows. Directional movement of shortfin eels is likely
to be for opportunistic feeding (Chisnall, 1989;
Chisnall & Hayes, 1991; Lasne et al., 2008), while
ınanga could be searching for refugia from high flow
velocities (Schwartz & Herricks, 2005) or alterna-
tively seeking shelter in wetland habitats where
predation pressure by larger fish is likely to be lower
than in the main channel (McDowall, 1990).
Aquatic insects and large-bodied zooplankton that
do not normally grow in flowing waters (Baranyi et al.,
2002; Kim et al., 2002; Collier & Lill, 2008) can
flourish in wetlands and floodplain retention zones
where they may serve as a suitable food source for
ınanga and other small-bodied fish species (McDo-
wall, 1990; Rowe et al., 2002). In tropical river
systems, with highly predictable flood pulses, feeding
migrations during floods are widely documented
(Benech & Penaz, 1995; Fernandes, 1997; Wantzen
et al., 2002; Castello, 2008). These lateral movements
between the main channel and riverine lakes and
wetlands have also been shown to play an essential
role in exchange of organic carbon between off-
channel and main river food webs (Burford et al.,
2008; Hunt et al., 2012). Conversely, in the smaller
Manu River in Peru, with more unpredictable, short-
duration flood pulses, fish moving into the off-channel
lake had full gut contents more often than fish leaving
the lake, suggesting the main channel can also be a
preferred feeding habitat (Osorio et al., 2011).
Common bully movements occurred predomi-
nantly during low flow conditions and higher summer
temperatures, when mostly juvenile bullies were
moving into the lake. This indicates that the produc-
tive Lake Whangape, and potentially other riverine
lakes with intact connections to the main river, may be
important for common bully which has an excellent
ability to maintain feeding in waters with low water
clarity (Rowe, 1999). Lakes such as Whangape may
also serve as a juvenile nursery. Interestingly, in
contrast to the main river channel and wetland, we did
not observe larger ([7 cm) common bullies at the lake
inlet, suggesting that the more structurally complex
main channel and wetland habitats are more suitable
Table 1 Mean (SE) for water quality parameters measured at
the study sites during sampling period (n = 17)
Location Temperature
(�C)
Specific
conductance
(lS cm-1)
Dissolved
oxygen
(mg l-1)
Main channel 17 (1.3) 148 (4.3) 7.2 (0.4)
Lake 18 (1.5) 191 (12.3) 8.0 (0.5)
Wetland 16 (0.7) 206 (6.3) 3.8 (0.5)
Hydrobiologia (2014) 729:161–174 167
123
Ta
ble
2N
um
ber
so
ffi
shsp
ecie
san
dfr
esh
wat
ersh
rim
pca
ug
ht
mo
vin
gin
toan
do
ut
of
the
mai
nri
ver
chan
nel
,an
dla
ke
and
wet
lan
do
ff-c
han
nel
hab
itat
so
ver
all
sam
pli
ng
dat
es
com
bin
ed
Sci
enti
fic
nam
eC
om
mo
nn
ame
InO
ut
Mai
nch
ann
elL
ake
Wet
lan
dM
ain
chan
nel
Lak
eW
etla
nd
No
.L
No
.L
No
.L
No
.L
No
.L
No
.L
Am
eiu
rus
neb
ulo
sus
(Les
ueu
r,1
81
9)a
Bro
wn
bu
llh
ead
catfi
sh–
–1
5.8
––
––
––
16
.6
An
gu
illa
au
stra
lis
(Ric
har
dso
n,
18
41)
Sh
ort
fin
eel
19
39
.4(4
.5)
13
13
9.9
(0.9
)2
55
29
.5(0
.8)
61
8.8
(8.5
)4
43
8.6
(1.3
)6
23
4.3
(1.8
)
An
gu
illa
die
ffen
ba
chii
(Gra
y,
1842)
Longfi
nee
l8
45.5
(2.1
)4
41.4
(2.3
)3
43.3
(6)
151.5
––
125.3
Ca
rass
ius
au
ratu
s(L
inn
aeu
s1
75
8)a
Go
ldfi
sh–
–9
5.7
(0.6
)–
––
–4
5.5
(1.4
)4
5.6
(1.4
)
Cyp
rinus
carp
io(L
inn
aeu
s,1
75
8)a
Co
mm
on
carp
––
17
.8–
––
–3
1.1
41
1.2
(0.0
3)
Ga
mb
usi
aa
ffin
is(B
aird
&G
irar
d,
18
53
)aG
ambu
sia
22
.9(0
.6)
36
3.1
(0.1
)–
–1
2.1
77
2.9
(0.1
)2
2.4
(0.2
)
Ga
laxi
as
ma
cula
tus
(Jen
yn
s,1
84
2)
Inan
ga
10
5.7
(0.2
)1
85
.8(0
.2)
18
7.5
(0.3
)4
4.4
(1.4
)2
15
.5(0
.3)
66
.5(0
.5)
Go
bio
mo
rph
us
coti
dia
nu
s(M
cDo
wal
l,1
97
5)
Co
mm
on
bu
lly
35
5(0
.7)
83
42
.4(0
.1)
12
34
.3(0
.2)
37
13
.1(0
.6)
29
63
(0.1
)3
05
4.7
(0.2
)
Ret
rop
inn
are
tro
pin
na
(Ric
har
dso
n,
18
48)
Co
mm
on
smel
t4
56
.2(0
.2)
15
.71
58
.1(0
.4)
11
6.1
(0.2
)2
66
.5(0
.3)
––
Sca
rdin
ius
eryt
hro
phth
alm
us
(Lin
nae
us,
17
58)a
Ru
dd
––
––
––
––
––
11
1.2
Pa
raty
acu
rvir
ost
ris
(Hel
ler,
18
62)
Fre
shw
ater
shri
mp
24
79
23
91
29
21
74
63
8
Av
erag
e(S
E)
tota
lle
ngth
(L)
of
spec
ies
caug
ht
isal
sosh
ow
na
Intr
odu
ced
spec
ies
168 Hydrobiologia (2014) 729:161–174
123
Table 3 PERMANOVA results conducted on CPUE for the fish community as well as four most abundant native fish and native
freshwater shrimp individually
Fish considered Source df SS Pseudo-F P
Community (all fish species) Location 2 7,556.4 5.5792 0.001
Date 5 8,860.6 2.6168 0.001
Location 9 date 10 10,482.0 1.5479 0.023
Residual 36 24,379.0
Anguilla australis Location 2 1,662.9 6.3287 0.004
Residual 36 4,729.7
Galaxias maculatus NS
Gobiomorphus cotidianus Location 2 4,649.0 13.914 0.001
Date 5 4,547.4 5.4441 0.001
Location 9 date 10 5,427.6 3.2489 0.002
Residual 36 6,014.1
Retropinna retropinna NS
Paratya curvirostris Location 2 958.0 4.0972 0.006
Date 5 2,687.6 4.5978 0.001
Location 9 date 10 8,588.8 7.3467 0.001
Residual 36 4,208.7
df Degrees of freedom, SS sums of squares, Pseudo-F distance-based pseudo F statistic, P probability values (obtained using 999
permutations of residuals under a reduced model)
Main channel
<10
10-1
920
-29
30-3
940
-49
50-5
960
-69
70-7
9
0
20
20
40
40
60
60
20
40
60
LakeAnguilla australis
<10
10-1
920
-29
30-3
940
-49
50-5
960
-69
70-7
9
Wetland
<10
10-1
920
-29
30-3
940
-49
50-5
960
-69
70-7
9
In
Out
In
Out
In
Out
Length class (cm)
<11-
1.92-
2.93-
3.94-
4.95-
5.96-
6.97-
7.98-
8.99-
9.9
10-1
0.9
11-1
1.9
12-1
2.9
Fre
qu
ency
(%
)
0
20
40
60
<11-
1.92-
2.93-
3.94-
4.95-
5.96-
6.97-
7.98-
8.99-
9.9
10-1
0.9
11-1
1.9
12-1
2.9 <1
1-1.
92-
2.93-
3.94-
4.95-
5.96-
6.97-
7.98-
8.99-
9.9
10-1
0.9
11-1
1.9
12-1
2.9
In
Out
In
Out
In
Out
Gobiomorphus cotidianus
Fig. 3 Length–frequency relationships of the two most abundant native species, shortfin eel (Anguilla australis) and common bully
(Gobiomorphus cotidianus), for each location and movement direction
Hydrobiologia (2014) 729:161–174 169
123
for adults of this species which can use aquatic
vegetation as a spawning substrate (McDowall, 1990).
Habitat complexity may also account to some
degree for the strong preference of freshwater shrimp
for wetland habitats with abundant vegetation
(Carpenter, 1982). Vegetated wetland habitats can
provide shelter from predation (Jordan et al., 1996;
Banha & Anastacio, 2011), as well as detritus and
periphyton as a source of food (Azim, 2005). Indeed,
shrimps moved in large numbers into and out of both
of the off-channel habitats, mainly during low flows
and high summer temperatures, suggesting dynamic
interactions between river and off-channel habitats for
this species, depending on environmental cues.
The role of temperature and water quality
As ectotherms, fish are generally more active at the
higher end of their preferred thermal optimum (Lucas
& Baras, 2001). This would explain the frequent
movements to off-channel habitats that we observed
during high discharge in spring, but not during winter
Table 4 Eigenvalues and cumulative percent variance explained
(in parentheses) from redundancy analyses (axes I–III) of habitat
type, flow magnitude and temperature explaining the abundance of
moving fish
Direction Pa Axes
I II III
In \0.01 0.450 0.036 0.015
(45) (48.6) (50.1)
Out \0.01 0.375 0.119 0.048
(37.5) (49.4) (54.3)
a Based on 999 permutations (test of significance of the first
canonical axis vs. all canonical axes gave the same results)
-1
0
1
-1 0 1
AX1
AX
2
G. cotidianus
G. maculatus
R. retropinna
A. australis G. affinis
Lake
Temperature
In
Wetland
Flow
Dissolved oxygen
Specificconductance
-1
0
1
-1 0 1
AX1
AX
2
G. cotidianus
G. maculatus
A. australis
G. affinis
LakeDissolved oxygen
Out
Wetland
Flow
C. carpio TemperatureSpecificconductance
Fig. 4 Redundancy
analyses of fish CPUE of
different species explained
by habitat type, flow
magnitude, temperature and
selected water quality
variables. The greater the
similarity in length and
direction of the vectors,
the stronger the association
between the abundance
of particular species and
associated environmental
characteristics
170 Hydrobiologia (2014) 729:161–174
123
when water temperatures remained low. Off-channel
habitats inundated during spring floods are often
warmer than the main river channel and thermally
heterogeneous (Gorski et al., 2010), suggesting inun-
dation may trigger movements in search of optimal
temperature regimes (Lucas & Baras, 2001). In
support of the role of thermal cues, adult barbel
Barbus barbus (Linnaeus, 1758) were shown to
progressively shift their diurnal pattern of feeding in
order to move to the foraging places at the time of the
day when water temperature is the closest to their
thermal optimum (Baras, 1995). In contrast to
Hohausova et al. (2003), who showed that water
quality parameters had little influence on fish move-
ment into off-channel habitats in the River Morava
(Czech Republic), we observed that variations in
specific conductance and dissolved oxygen between
different off-channel habitats could partly explain fish
movement into and out of these habitats. This finding
indicates that, after the governing roles of flow and
temperature are accounted for, other environmental
characteristics that define off-channel habitats (i.e.
water quality) may also play a role in initiating fish
movement. In support of this, North American
centrarchids overwintering in backwater lakes on the
upper Mississippi River were shown to move out of
lentic areas when oxygen levels dropped below
2 mg l-1 (Knights et al., 1995). Similarly, higher
numbers of common bullies moving into the lake
habitat in our study could, to some extent, reflect a
preference for turbid waters (Rowe, 1999). Factors
stimulating fish migration and movement are complex
(Lucas & Baras, 2001), with multiple cues working in
concert, and movement occurring when factors pro-
moting residency are outweighed by those stimulating
movement, irrespective of the physiological or envi-
ronmental nature of those cues (Ovidio et al., 1998).
Management implications
This study emphasises the importance of lateral
hydrologic connectivity and seasonal flooding of off-
channel habitats in the functioning of this southern
hemisphere temperate large river system, as demon-
strated by the numerous native fish using the lake and
wetland during the flood and at low flows. Therefore,
management strategies that promote connectivity
within lowland river–floodplain ecosystems and reha-
bilitate (semi-)natural flow dynamics are likely to
maximise habitat availability and feeding opportunities
for key life stages of native fish as well as providing
refugia at important times of year. Similar findings have
been shown for large European rivers (Lasne et al.,
2007), where numbers of native species increased with
increasing connectivity. Furthermore, body condition
of European eels Anguilla anguilla (Linnaeus, 1758)
has been shown to decrease with decreasing lateral
connectivity (Lasne et al., 2008), potentially because
inundated terrestrial habitats provided food of better
nutritional quality (Van Liefferinge et al., 2012). A
similar reliance on lateral connectivity with wetlands is
supported for shortfin eels in the lower Waikato River
(Chisnall & Hayes, 1991).
However, high numbers of non-native larval com-
mon carp moved out of the wetland with retreating
flood water, and the introduced gambusia was
recorded in both off-channel habitats through the
year. Maintenance of high flows and artificial floods
may potentially be important for preservation of native
fish communities in river systems in which most of the
introduced fish species are adapted to lentic conditions
(Bernardo et al., 2003). In the lower Waikato River,
however, flooded wetland habitats appear to serve as
superior spawning habitat for phytophilic common
carp whose larvae were highly abundant moving out
of the wetland with receding spring floods, as has
also been observed for this species in the Australian
Murray River (Stuart & Jones, 2006). Indeed, adult
common carp were recorded to move frequently to off-
channel habitats during spring spawning time in both
the Australian Murray River (Jones & Stuart, 2009)
and the lower Waikato River (Daniel et al., 2011).
Therefore, to be successful, management aimed at
enhancing ecological integrity must consider the
potential negative and ongoing implications of non-
native fish movement and reproduction in off-channel
habitats, which our study has shown can provide
important nurseries for invasive common carp. Para-
doxically, main channel–off-channel connections can
serve as natural movement bottlenecks for such
species and therefore may provide opportunities for
targeted control of non-native invasive fish species
during movement phases. Appropriate management
of floodplain ecosystems may therefore involve
implementing ‘controlled connectivity’ measures that
provide access for native species at key times while
limiting opportunities for introduced species to utilise
favoured off-channel habitats.
Hydrobiologia (2014) 729:161–174 171
123
Acknowledgments We thank Courtney Kellock, Warrick
Powrie, Ray Tana, Michael Pingram and Dudley Bell
(University of Waikato) for assistance during field sampling.
Funding for this work was provided by the Strategic Investment
Fund of the University of Waikato.
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