Evaluating the potential of the Nagambie Lakes for golden

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					No. 4, September 2007                                                                            ISSN 1833 - 7066

Evaluating the potential of the Nagambie Lakes
for golden perch and Murray cod.
The Nagambie Lakes, just an hour’s drive north                  raised fish may not always be advantageous.
of Melbourne, has the potential to be a favourite
haunt of recreational anglers targeting native
fish.
To maximise this potential Fisheries Victoria and the
Nagambie Angling Club tried to establish a self-sustaining
(reproducing) native fishery. They did this by releasing
around 440,000 small fish, mostly golden perch, into the
lake system from 1979 to 1994. But the fish would not
cooperate and little evidence of them still remain!
Formed to regulate irrigation supplies for Shepparton,
Central Goulburn, Rochester and the irrigation system of
the Waranga Basin, this lake has a range of deep channel
and shallow backwater habitats, which were thought to be
suitable for native fish.
To work out what the Nagambie Lake system was lacking
from a fish’s perspective, researchers from the Arthur
Rylah Institute for Environmental Research decided to go
right to the source and ask the fish!
Thirty-two Murray cod and fifteen golden perch were
enlisted, fitted with radio tags and released into the middle
of the Lake system at Picnic Point, Kirwins Bridge and
Bazley Island (see map in next column).
With the aid of five radio tracking logger stations set up
through out the lake, the scientists were able to see what
the fish were doing and where they were going during the
ten-month study.
                                                                Map showing locations of research sites
The response of the Murray cod to being released into the
Nagambie Lakes was to stay put!                                 The golden perch, sourced from the lower Goulburn River
                                                                below Goulburn Weir, adapted much better to the lake
The hatchery reared Murray cod tended to be fairly
                                                                environment than did the Murray cod.
sedentary and perhaps failed to come to terms with a
natural lake environment. Many died during the course of        Golden perch were highly mobile throughout the course
the study. While predators (most likely pelicans),              of the study, most undertaking long upstream and
probably ate many, the researchers felt that the Murray         downstream migrations. Only one fish remained in the
cod’s hatchery upbringing compromised their ability to          location where it was released. Many fish swam more
escape from predators and even to hunt for food. This           than 3 km to explore downstream gates and several left
finding indicates that the stocking of larger, hatchery         the lake system escaping through control gates on
irrigation channels.                                         food species that were available for golden perch and
                                                             Murray cod within the lake system. Crustaceans such as
Interestingly, there was one control gate through which      yabbies, freshwater prawn and shrimp and small fish such
golden perch would not venture even though many fish         as flat-headed gudgeon, carp gudgeon and smelt presented
approached it on many occasions. It is possible that gate    a smorsgeboard of choice for both golden perch and
configuration and associated features, such as turbulence    Murray Cod.
and noise, can greatly influence the decision of golden
perch looking to exit large impoundments via irrigation      The food available to golden perch and Murray cod within
release points.                                              the Nagambie Lakes system was less abundant than in the
                                                             lower Goulburn River.
Both the golden perch and Murray cod released into the
lakes were strongly associated with the main river channel   By asking the fish, scientists were able to identify the
and were found 90% and 70% of the time respectively in       following factors that probably prevented Murray cod and
the deeper water. In this deeper water, both golden perch    golden perch from successfully establishing self-
and Murray cod were always found close by some form of       sustaining populations in the Nagambie Lakes system:
in-stream structure, most often large woody debris.           •    Fish were moving upstream into the river and
Neither the Murray cod nor golden perch released into the          downstream via irrigation channel outlets;
Nagambie Lakes used backwater habitats to any great           •    The limited extent of deep-water habitat with in-
extent, possibly because these habitats were too shallow           stream structures such as large woody debris;
due to the accumulation of sediment.                          •    Cold incoming water causing rapid temperature
                                                                   fluctuations in spring and summer; and
In addition to finding out what the fish were doing, the
researchers also looked at environmental conditions           •    A lack of connectivity between the backwater and
within the Nagambie Lake system.                                   the deep-water channel habitats, thereby reducing
                                                                   access to potential spawning and nursery habitat.
A series of continuous temperature loggers were installed
at a number of places around the lake they collected other   Recreational Fishing Licence revenue funded this research
information on a monthly basis, which further described      project.
the quality of the lake for golden perch and Murray cod.     For further information about this project please contact
Both Murray cod and golden perch spawn when water            Justin O’Mahony, at Arthur Rylah Institute for
temperatures are around 23°C. The researchers found that     Environmental Research on (03) 9450 8600.
water temperatures suitable for spawning were achieved       Contact the FRAC Secretariat during business hours on
in the backwater habitats during summer but not in the       9658 4369.
deeper water channel habitats where the released fish
spent most of their time.
The researchers also noticed that while the water
temperatures began to increase from mid-September,
releases of irrigation water over the summer months
caused water temperatures across the lakes system to
drop. During the study, in January 2003, water
temperatures across system decreased by 6 to 9°C over
eight days.
Unseasonal temperature fluctuations like these are likely
to further reduce the ability of golden perch and Murray
cod to successfully reproduce within the Nagambie Lakes.
The scientists also described the quantity and variety of

				
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