Land and Water Link
September 2002
 Plastic
'Plants' Help Native Fish
Artificial plants are being introduced to various sites along Victoria's
Broken River to test the significance of submerged plants in improving
food and habitat availability for native fish populations. The plastic
plants mimic ribbon weed (Vallisneria spp), a common water plant
native to Australia.
CSIRO Land and Water researchers from the Murray-Darling
Freshwater Research Centre based in Albury are installing these artificial
plants in sections of the river as part of their quest to determine factors
that might be used to boost numbers of larval and juvenile fish.
As Dr Chester Merrick explains, 'One possible contribution to the decline
in native fish populations may be via the loss of submerged aquatic plants.
We are testing this possibility by using artificial plants to replicate
and increase the amount of the river plant life that is vital to sustaining
native fish populations.'
Continuing river degradation has contributed to the widespread loss of
underwater plants from many Australian lowland rivers, and this in turn
is thought to have had an impact on both fish reproduction and the survival
of young native fish.
Dr Merrick explains that numerous changes to our riverine systems have
adversely affected aquatic plant life. 'Eroding riverbanks have created
large sand 'slugs' that move down the river and bury the plants. Increasing
turbidity or muddiness has reduced the amount of light available for plant
growth on the riverbed, and higher nutrient loads have caused excessive
algal growth on the underwater plants, which can smother and kill them.'
Changes in seasonal flow patterns and water quality brought about by river
damming and regulation are known to have impacted on native fish populations
in many lowland rivers. However the precise mechanisms behind the impacts
are not fully understood.
'Lowland river rehabilitation often involves restoring critical habitat
for fish, and despite a perception that snags are the most important type
of fish habitat, fish are also found near underwater plants', says Dr
Merrick. 'Through this research, we are trying to ascertain the importance
of the part they play.'
Submerged aquatic plants offer young fish shelter from currents and predators.
In addition, the plant leaves and stems offer a stable surface for algal
growth, which in turn is a crucial part of the aquatic food chain.
The research team is using plants made from plastic because there are
not enough natural submerged plants available. Artificial plants will
allow experimental replication and easy manipulation of characteristics
such as patch size and stem density as changes in riverine primary productivity,
invertebrate numbers and larval and juvenile fish numbers are measured.
Researchers installed the artificial plants into sites on the Broken River,
where they already know there are populations of 10 native and four introduced
fish species, and fish spawning times are well understood. Samples of
the larval and juvenile fish associated with the artificial plants will
be compared to control samples taken from unvegetated areas immediately
upstream.
According to Dr Merrick, 'The project should show us the linkages between
submerged plants and fish numbers. We hope to use this knowledge to improve
river management practices for lowland rivers, so as to better sustain
fish and submerged plants.'
The project is funded by the Natural
Heritage Trust through the AFFA
Murray-Darling Fish Rehabilitation Program and by the Goulburn-Broken
Catchment Management Authority.
For further information
Contacts:
Contact
Dr Chester Merrick
Ph: 02 6058 2362
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