Population assessment of Trout Cod and sympatric
fish species within the closed section of
Seven Creeks during 1997.
S.R.Saddlier and D.J.Harrington
December 1997
Marine and Freshwater Resources Institute
123 Brown St. Heidelberg, 3084
TABLE OF CONTENTS
page no.
List of Figures
ii
List of Tables
iii
Summary
iv
Introduction
1
Methods
Sampling sites
Sampling methods
4
4
4
Results
5
Total Numbers of Fish Captured
5
Native Freshwater Fish
Trout Cod
Freshwater Blackfish
Macquarie Perch
Mountain Galaxias
Australian Smelt
Southern Pigmy Perch
7
7
7
8
8
8
8
Decapod Crustacea
Spiny Freshwater Crayfish
Yabby
9
9
9
Introduced Freshwater Fish
Brown Trout
English Perch
Carp
Mosquitofish
9
9
10
10
10
Trout Cod length-frequency distribution (sites combined)
Trout Cod length-frequency distribution at individual sites
15
15
Discussion
Current survey results
Comparison with 1991 data
20
20
23
Acknowledgements
24
References
25
i
LIST OF FIGURES
page no.
Figure 1.
Map of the Goulburn River system, with Seven Creeks highlighted in
yellow (map taken from Tunbridge and Glenane, 1994).
2
Figure 2.
Upper section of Seven Creeks, showing associated tributaries and sections
where fish surveys were conducted between 28 April and 18 June 1997
3
Figure 3.
Total numbers of each fish species captured from Seven Creeks during 1997.
6
Figure 4.
Total numbers of Trout Cod captured from each site within Seven Creeks
during 1997.
6
Figure 5.
Density of each fish species (fish per 100m) captured from sites C&D
during 1997.
11
Figure 6.
Density of each fish species (fish per 100m) captured from site E during 1997.
11
Figure 7.
Density of each fish species (fish per 100m) captured from site F during 1997.
11
Figure 8.
Density of each fish species (fish per 100m) captured from site G during 1997.
12
Figure 9.
Density of each fish species (fish per 100m) captured from site H during 1997.
12
Figure 10.
Density of each fish species (fish per 100m) captured from site I during 1997.
12
Figure 11.
Density of each fish species (fish per 100m) captured from site J during 1997.
13
Figure 12.
Density of each fish species (fish per 100m) captured from site K during 1997.
13
Figure 13.
Density of each fish species (fish per 100m) captured from site L during 1997.
13
Figure 14.
Density of each fish species (fish per 100m) captured from site M during 1997.
14
Figure 15.
Length-frequency of Trout Cod captured from all sections (combined data)
16
Figure 16.
Length-frequency of Trout Cod captured from site H
17
Figure 17.
Length-frequency of Trout Cod captured from site I
17
Figure 18.
Length-frequency of Trout Cod captured from site J
17
Figure 19.
Length-frequency of Trout Cod captured from site K
18
Figure 20.
Length-frequency of Trout Cod captured from site L
18
Figure 21.
Length-frequency of Trout Cod captured from site M
18
Figure 22.
Estimated Trout Cod density (fish/100m) calculated at each site
for 1991 and 1997.
19
ii
LIST OF TABLES
page no.
Table 1.
Presence ( ) or absence (-) of fish species captured at each of the
10 sites surveyed in Seven Creeks during 1997 (shading indicates
native fish species)
iii
5
SUMMARY
A total of 12 species of freshwater fish were captured from the 10 sections surveyed
within Seven Creeks, including six species of native freshwater fish, two species of
native decapod crustacea and four species of introduced freshwater fish.
Of the
native fish, Trout cod Maccullochella macquariensis represented the most abundant
species with a total of 412 fish captured from all sites, followed (in decreasing
abundance) by Freshwater blackfish Gadopsis marmoratus (231 fish), Macquarie
perch Macquaria australasica (103 fish), Southern pygmy perch Nannoperca
australis (17 fish), Mountain galaxias Galaxias olidus (12 fish) and Australian smelt
Retropinna semoni (1 fish). Two species of decapod crustaceans were also captured,
including a total of 50 Spiny freshwater crayfish Euastacus armartus and 13
specimens of the Yabby Cherax destructor.
Four species of introduced freshwater
fish were also captured, including Carp Cyprinus carpio (75 fish), Brown trout Salmo
trutta (69 fish), English perch Perca fluviatilis, (56 fish) and one specimen of the
Mosquitofish Gambusia holbrookii.
Distribution of Trout Cod varied significantly over the length of the survey area. No
Trout cod were captured from the upper reaches of the study site (sections C, D, E, F
and G), while progressively higher densities of Trout cod were observed further
downstream of these sites, ranging from 1.1 fish per 100 metre section at site H to the
highest density of 22.1 fish per 100 metre section at site L. A strong correlation was
observed between increasing Trout cod density and progressive distance downstream
from site H.
However, this correlation does not apply to the lowest site (site M)
where Trout cod density decreases from 22.1 fish/100m to 3.8 fish/100m.
Trout cod length-frequency distribution data indicate that very strong recruitment
occurred in the 1996 spawning season, with fish within the 50 - 80mm length class
comprising 48% of the total numbers of Trout cod captured. Length-frequency data
also suggests that recruitment over the past three spawning seasons has been
consistent, as indicated by a broad distribution of fish ranging from 100 - 200 mm in
length. Although age-length data is not available for Trout cod collected from Seven
iv
Creeks, year classes (determined from length-frequency graphs) appear to indicate that
fish ranging from 100 - 200 mm in length correspond to 1+ to 2+ age classes.
Information collected from Seven Creeks during the current survey indicate that of all
the trout cod captured, those which are presumed to be of a sexually mature length
constitute only 9% of the entire catch and represent a total of 35 fish.
Assuming a
sex ratio within the population of 1:1, a total of 35 mature size fish corresponds to
approximately 17 potential spawning pairs captured. This number of mature size fish
is in contrast to that of a survey conducted in 1991 where a total of 42 fish were of a
mature size, representing 25% of the entire Trout cod population captured.
v
INTRODUCTION
The headwaters of Seven Creeks originate in the Strathbogie Ranges approximately
130 km NNE of Melbourne, initially flowing South-West through predominantly
granitic country for a distance of approximately 35 km before heading NNW through
the township of Euroa to meet with the Goulburn River approximately 5 km upstream
of the township of Shepparton (Figure 1).
The upper reaches of Seven Creeks supports the only viable Victorian population of
the nationally endangered Trout Cod Maccullochella macquariensis which was
translocated from the Goulburn river in 1921-22 (DCNR 1995).
This population is
restricted to a relatively small section of Seven Creeks which extends between Polly
McQuinns Weir, downstream to the crossing of Galls Gap Road below Watchbox
Creek, covering a distance of approximately 11 kilometers (Figure 2). The majority
of this section of Seven Creeks has a riparian zone which is fenced off to cattle access,
or is protected within the Gooram Falls Reserve apart from a section extending
approximately 2 kilometers downstream from Polly McQuinns Weir.
As one of the actions recommended by the National Trout Cod Recovery Team, a fish
population survey was conducted in this section of Seven Creeks between 28 April
and 18 June 1997 to determine the current population status of this species, as well as
the status of other fish species present in this section of Seven Creeks.
1
Figure 1.
Map of the Goulburn River system, with Seven Creeks highlighted in yellow
(map taken from Tunbridge and Glenane, 1994).
2
Figure 2.
Upper section of Seven Creeks, showing associated tributaries and sections
where fish surveys were conducted between 28 April and 18 June 1997
3
METHODS
Sampling sites
A total of ten sampling sites were surveyed within Seven Creeks following
nomenclature used by Anderson (1991).
The study area extends between Polly
McQuinns Weir, downstream to the crossing of Galls Gap Road below Watchbox
Creek, covering a distance of approximately 11 kilometers (Figures 1 and 2).
Sampling methods
The fish fauna of Seven Creeks was assessed using two fish sampling techniques. At
shallow sites which were easily wadeable, fish were sampled using a fully portable
Smith-Root Model 12 backpack electrofisher. Electrofishing was the preferred
sampling technique due to its relative lack of species selectivity. Sites F, H and I
contained waters which (due to depth) could not be electrofished effectively. At these
sites, single wing fyke nets were used. Fyke nets are more selective for benthic
species which move around the margins of waters where they are likely to be
captured. Because of this requirement, catch results from fyke nets may not accurately
reflect actual ratios of all species within a given area and must be interpreted with
caution.
4
RESULTS
Total numbers of fish captured
A total of six species of native freshwater fish were captured from Seven Creeks
during this survey (table 1). These species include Trout cod Maccullochella
macquariensis which represent the most abundant species with a total of 412 captured
from all sites (Figure 3). Freshwater blackfish Gadopsis marmoratus (231 fish) were
the next most abundant species, followed by Macquarie perch Macquaria australasica
(103 fish). The remaining three species of native freshwater fish were represented by
low numbers of fish, with 17 specimens of Southern pygmy perch Nannoperca
australis, 12 specimens of Mountain galaxias Galaxias olidus and a single specimen
of Australian smelt Retropinna semoni captured. Two species of decapod crustaceans
were also captured, including a total of 50 Spiny freshwater crayfish Euastacus
armartus and 13 specimens of the Yabby Cherax destructor.
Four species of
introduced freshwater fish were also recorded, including Carp Cyprinus carpio (75
fish), Brown trout Salmo trutta (69 fish), English perch Perca fluviatilis, (56 fish) and
one Mosquitofish Gambusia holbrookii.
SPECIES
C/D
E
F
G
Trout cod
-
-
-
-
Site
H
I
J
K
L
M
Macquarie perch
Freshwater blackfish
-
Mountain galaxias
-
-
-
-
Australian smelt
-
-
-
-
-
-
-
-
Southern pygmy perch
-
-
-
-
-
-
-
-
-
-
-
-
Spiny freshwater crayfish
-
-
-
-
Yabby
-
-
-
-
-
-
-
-
Brown trout
-
-
English perch
-
-
-
-
-
-
-
-
Carp
-
-
-
-
-
-
-
-
-
Mosquito fish
-
-
-
-
-
-
-
-
-
Upstream------------------------------------Downstream
Table 1. Presence ( ) or absence (-) of fish species captured at each of the 10 sites surveyed in
Seven Creeks during 1997(shading indicates native fish species)
5
6
Native Freshwater Fish
The density (represented as number of fish per 100 metre section of stream) of
individual fish species captured at each site is presented in Figures 5 - 14.
Trout Cod
A comparison of Trout cod density at each site indicates a surprising lack of fish in the
upper reaches of Seven Creeks. Trout cod were not recorded at sites C/D, E, F or G.
Site H (immediately downstream of site G) supports low numbers of Trout cod (1.1
fish/100m) while 10.3 fish/100m were captured from site I (figure 4).
This
progressive increase in density continues in a downstream direction until a maximum
density of 22.1 fish/100m was observed at site L. The lowest site (site M) support far
lower densities of Trout cod with 3.8 fish/100m being captured. This site is unique
within the study area in supporting moderate densities of Carp (2.74 fish/100m) which
were not recorded from any other sites within the survey. A comparison of the habitat
at sites throughout the study area indicates that this lowest site is in a more degraded
condition compared to sites upstream, with large amounts of sand being present and
subsequently less variation in instream habitat.
Freshwater Blackfish
Freshwater blackfish were captured from all sites apart from site J. The lowest three
sites (sites K, L and M) support similar densities of this species with 3.6, 3.1 and 3.5
fish/100m respectively, while sites further upstream (G, H, and I) possess lower
densities of blackfish (0.44, 1.67 and 2.0 fish/100m). The three sites situated highest
in the study area (C/D, E and F) were surveyed predominantly using fyke nets,
combined with a low level of electrofishing where possible.
Fyke nets are
particularly effective for benthic species such as blackfish and consequently results
may reflect higher densities of this species at 5.3, 6 and 4.4 fish/100m at sites C/D, E
and F respectively.
7
Macquarie Perch
Macquarie perch were also distributed throughout the study area, being captured at
densities ranging from 0.17 fish/100m at site I to 6.2 fish/100m at site F. Generally,
the density of Macquarie perch was high in the lower reaches of the survey area (sites
M, L and K) with 1.0, 2.1 and 1.7 fish/100m being captured, dropping in the mid
reaches (sites J, I, H and G) to 0.7, 0.2 and 0.3 fish/100m respectively.
The upper
sites (sites C/D, E and F) provided relatively high catch levels of 2.7, 3.2 and 6.2
fish/100m, although, as was the case for Freshwater blackfish, the predominant use of
fyke nets may be the reason for recording higher densities.
Mountain Galaxias
Very low numbers of Mountain galaxias were recorded at only four of the ten sites
surveyed, including the lowest sites, L and M where densities of only 1.3 and 0.2
fish/100m were observed(figures 13 and 14). One specimen was captured at site H
and site I, corresponding to densities of 0.04 and 0.2 fish/100m respectively (figures 9
and 10).
Australian Smelt
One Australian smelt was captured at the lowest site (site M), corresponding to a
density of 0.04 fish/100m.
Southern Pygmy Perch
Southern pygmy perch were restricted to the upper two sites, where a total of 15 fish
were captured from site E (a density of 6.0 fish/100m) and a further 2 fish were
captured from the highest site surveyed (site C/D), at a density of 1.33 fish/100m.
8
DECAPOD CRUSTACEA
Spiny Freshwater Crayfish
Spiny freshwater crayfish Euastacus armartus were captured from sites H, K, L and
M.
Densities varied significantly across the survey area, with low numbers being
captured from the lowest sites within Seven Creeks (sites K, L and M) where 0.4, 1.0
and 0.1 fish/100m were captured, compared to the higher density (1.8 fish/100m),
observed at site H.
Yabby
The Yabby Cherax destructor was only captured from the lowest site (site M), at a
density of 0.5 fish/100m.
Introduced Freshwater Fish
Brown Trout
Brown trout were ubiquitous throughout the survey area, apart from site F where none
were captured. Densities were highest at those sites situated furthest downstream
where 1.0, 2.3 and 0.4 fish/100m were captured from sites M, L and K respectively,
and from those sites situated furthest upstream (sites C/D and E), where 10 and 1.6
fish/100m were captured.
Far lower densities of brown trout were observed in the
mid reaches of the survey area (G, H, I and J) where 0.2, 0.2, 0.5 and 0.3 fish/100m
were captured respectively.
9
English Perch
The distribution of English perch is restricted to below Gooram Falls (sites L and M),
with high numbers of this species being captured from the lowest site (site M) at a
density of 1.9 fish/100m. Site L supports lower numbers of this species, being
captured at a density of 0.8 fish/100m.
Carp
Site M was the only site in which Carp were captured during this current survey. As
with English perch, it appears Gooram Falls may present a barrier to the upstream
movement of this species. The slower moving waters found in site M also appear to
be more suitable to this species which tends to prefer pools and deeper slow moving
waters which are found at site M.
Mosquito Fish
Only one specimen of Mosquito fish was recorded in this survey at site H.
10
11
12
13
14
Trout Cod Length-Frequency Distribution (sites combined)
The length-frequency distribution of Trout cod (all sites combined) is presented in
Figure 15. High numbers of Trout cod from the smallest length class were observed,
with fish within the 50 - 80 mm length class comprising 48% of the total number of
Trout cod captured (192 fish). Fish within this first year class (representing ages of
approximately 6 - 7 months), average a length of approximately 64 mm and are quite
distinctly separated from the following year class of fish which are approximately 18
months of age.
Fish within this 1+ age class range from a length of 103 mm to
approximately 160 mm, although a small number of larger individuals from this group
appear to merge with smaller individuals of the next (2+) year class. Trout cod from
larger length classes (3+ and greater) are less distinct again and no conclusion can be
drawn from the population structure in the absence of verified age data.
Trout Cod Length-Frequency at Individual Sites
The length-frequency distribution of Trout cod at individual sites are presented in
Figures 16 - 21.
Results indicate that 0+ Trout cod constitute the greatest proportion
of the total captured populations at sites H, I, J and K, comprising 88%, 58%, 59%
and 81% of total Trout cod numbers at each site respectively.
Sections downstream
of site K (sites L and M) exhibit decreasing proportions of this length class, with 0+
fish comprising 35% of the entire population sampled at site L and 13% at site M.
The distribution of 1+ Trout cod within Seven Creek exhibits very different
characteristics to that of 0+ fish. Very low proportions of 1+ fish were present within
the mid-sections of the study area. The proportion of 1+ fish at sites H, I, J and K
were 8%, 9%, 6% and 9% respectively, whereas at sites L and M, this proportion
increased to 19% and 29%.
15
Trout cod which fell into the size range of 100 mm - 250 mm (i.e. those individuals
which were at least 2+ years of age but which are presumed to be sexually immature)
were absent from catch results obtained from the highest site supporting a population
of Trout cod (site H). This size class was represented at sites I and J by 22% and 31%
respectively, before dropping to only 7% at site K.
Higher proportions of these
immature size fish were present at sites L and M where they comprise 32% and 45%
of the entire Trout cod population captured.
The remaining fish (representing size ranges of 251 - 590 mm) captured at each site
are presumed to be sexually mature (Cadwallader, 1977). These fish comprise a very
small proportion of the entire Trout cod population at each site, including 4% at site
H, 11% at site I and 3% at sites J and K. Slightly higher proportions were observed
at site L and site M where 14% and 13% were captured respectively.
16
17
18
19
DISCUSSION
Current survey results
There was a clear increase in the density of Trout cod moving downstream from site H
to site L (1.1 to 22.1 fish/100m), however at the lowest site (site M), a density of only
3.8 fish/100m was recorded. No fish were captured above site H.
Habitat within the section of Seven Creeks above Gooram Falls (above site H) is
predominantly characterised by large pools, which are either sand based where water
velocities are low, or granite based where velocities are high. These pools are most
often linked by either rock (granite) chutes and falls, or by riffle sections possessing a
boulder/cobble base.
This substrate variation provides extensive habitat diversity for
aquatic fauna within this section of Seven Creeks.
This habitat diversity does not
exist within the study area below Gooram Falls (site M), where due to a combination
of reduced stream fall and poor land management practices (which have recently been
addressed by local LandCare groups), high levels of sand have entered the system,
filling pools and generally covering the substrate.
Presumably this lack of habitat
diversity affects the distribution of trout cod, a species which establish well defined
territories (Cadwallader and Gooley, 1984) and appears to be highly dependant upon
adequate habitat availability in Seven Creeks.
Drifting Trout cod larvae were first observed in Seven Creeks on 14th December 1995
(S. Saddlier, pers. obs. 1995) which indicates spawning may have occurred from late
November to early December. Assuming that the time of spawning does not vary
dramatically from year to year, young of the year Trout cod (having an average length
of 64 mm) captured between 28 April and 18 June would therefore represent fish of
approximately 5 - 6.5 months of age.
This approximate age for length information
varies slightly in comparison to data collected on the age of juvenile Trout cod from
the Murray River (assessed at the National Ageing Facility at Queenscliff), which
calculates juveniles of the same length (64mm) at 121 days (approximately 4 months).
20
This size for age contrast may indicate a variation in growth rates between the two
sites, or may indicate that the time of spawning at Seven Creeks varies substantially
from year to year.
Further conclusions may be drawn from information which is
currently being produced at the National Ageing Facility at Queenscliff, where
specimens of juvenile Trout Cod captured from Seven Creeks during this survey are
being aged.
Although very little age-length data is available for Trout cod collected from Seven
Creeks, year classes (determined from length-frequency graphs) appear to indicate that
the high proportion of fish within the entire population from this smallest length class
(50 - 80 mm) reflect strong recruitment in the 1996 spawning season.
This length-
frequency data also suggests that recruitment over the past three spawning seasons has
been consistent, as indicated by the broad distribution of fish ranging from 110 - 260
mm in length.
Little information is available on the size of trout cod at maturity, particularly for fish
in the wild. However Trout cod captured from the Murray River at Yarrawonga
during 1949-50 were in spawning condition at 254 mm in length (Cadwallader, 1977).
During the current survey in Seven Creeks of the total numbers of trout cod captured,
those which are greater than 254 mm in total length constitued only 9% of the entire
catch and represented a total of 35 fish.
Assuming a sex ratio within the population
of 1:1, a total of 35 mature size fish corresponds to approximately 17 potential
spawning pairs captured.
This number of mature size fish suggests a very small
breeding population of Trout cod is present, particularly considering that this
population is distributed over a stretch of approximately six km of Seven Creeks and
is to a large extent “compartmentalised” as a result of the presence of natural instream
barriers which prevent the upstream movement of this species.
The distribution of other fish species varied markedly throughout the study area.
Other native species include Macquarie perch and Freshwater blackfish which were
ubiquetous in catch results, although higher densities were observed in the higher
sections surveyed.
21
These higher densities may in-part be attributed to the use of fyke nets as the dominant
sampling technique, as this method is particularly effective for catching both
Macquarie perch and Freshwater blackfish. Fyke nets were used in these sections due
to a general change in habitat conditions, with an increase in larger, deeper pools,
making electrofishing very difficult and relatively inneficient.
This habitat is
favourable to species such as Freshwater blackfish (Jackson, 1978) and Macquarie
perch (Cadwallader, 1981), giving rise to the increased abundance of these species in
catch results from the higher sections surveyed.
However, without standardised
sampling throughout the sections, quantitative assessments of the densities of these
two species should be interpreted with caution.
Introduced species also show marked variation in densities, with English perch and
Carp only recorded below Gooram Falls.
Gooram Falls represents a barrier to the
upstream movement of these species, effectively isolating them from waters above the
falls area.
22
Comparison with 1991 data
A survey of the fish fauna of the upper Seven Creeks area was conducted during 1991
by staff of the Kaiela Fisheries Research Station (Anderson, J.R. 1991). This survey
was conducted as part of an ongoing monitoring program, as well as an attempt to
determine the impact which bush fires (which occurred during late December 1990)
may have had on the instream fauna of Seven Creeks.
Although it is difficult to
draw conclusions based on a comparison of the total numbers of each fish species
captured during the two sampling events due to variations in electrofishing and netting
efficiencies, useful comparisons can be made on the relative proportions of fish
species captured from each section and in particular on the relative proportions of
each length class of Trout cod captured throughout the survey.
Preliminary comparisons indicate that while Trout cod densities were similar at sites
G - J during both surveys (Figure 22), sites situated further downstream (sites K, L
and M) exhibited marked variation.
Highest Trout cod densities were observed at
site J during the 1991 survey, progressively decreasing with increasing distance
downstream, while in the 1997 survey, densities progressively increased to a
maximum at site L, before decreasing dramatically at the lowest site (site M). This
trend appears to reflect a downstream movement of the Trout cod population, with the
highest densities currently being observed at sites which in 1991 supported relatively
low proportions of Trout cod.
23
ACKNOWLEDGEMENTS
Assistance in the field was provided by P. Fairbrother, T. Glenane, J. Lieschke, J.
Mahoney and D. O’Mahony. Thanks also to Bill O’Connor and Pam Clunie for their
valuable comments on the report.
24
REFERENCES
Anderson, J.R. 1991 (Draft Report) Status of the protected population of Trout Cod
(Maccullochella macquariensis) and other native fish in the upper reaches of Seven
Creeks, Victoria, in 1991. Kaiela Fisheries Research Station, Flora and Fauna
Division, Dept. of Conservation and Environment, Victoria.
Cadwallader, P.L. (1977) J. O. Langtry’s 1949-50 Murray River Investigations.
Fisheries and Wldlife Paper, Victoria. No. 13, 70pp.
Cadwallader, P.L. (1981) Past and present distributions and translocations of
Macquarie perch Macquaria australasica (Pisces : Percichthidae), with particular
reference to Victoria. Proceedings of the Royal Society of Victoria. 93: 23-30.
Cadwallader, P.L. and Gooley, G.J. (1984). Past and present distributions and
translocations of Murray Cod Macculochella peeli and Trout Cod Macculochella
macquariensis (Pisces : Percichthyidae) in Victoria. Proc.R.Soc. Vic. 96 : 33-43.
Department of Conservation and Natural Resources
Maccullochella macquariensis. Action Statement No. 38.
(1995).
Trout
Cod
Jackson, P. D. (1978) Benthic invertebrate fauna and feeding relationships of brown
trout Salmo trutta Linnaeus, and river blackfish Gadopsis Marmoratus Richardson,
in the Aberfeldy River, Victoria. Australian Journal of Marine and Freshwater
Research. 29: 725-742.
Tunbridge , B.R and Glenane, T.G. (1982) Fisheries Value and Classification of
Fresh and Estuarine Waters in Victoria. Fisheries and Wildlife Division, Ministry
For Conservation, Arthur Rylah Institute for Environmental Research.
25