Six rivers within the upper Mumbidgee catchment were sampled for larval and juvenile
fish. The rivers represented both regulated and unregulated flow regimes and varied widely in
size. There was wide variation in the larval fish communities supported by each river, both in
terms of the species diversity and total abundance of fish sampled. The highly regulated reach
of the Mumbidgee River sampled during this study had the highest numbers of native
species and native individuals of any river sampled.
In the two rivers selected for further study, the Murmmbidgee and Goodradigbee, there was a
high level of inter-annual consistency in the species composition within the reaches sampled,
despite considerable change in the temperature and flow regimes of both rivers. This indicates
that at least some spawning of those species sampled may occur each year, regardless of
environmental conditions. Estimates of the relative abundance of each species sampled
changed markedly between years, and it is argued, on the basis of growth information
contained in the otoliths, that differential survival of larvae and juveniles was largely
responsible for this shift in relative abundance.
Otolith microstructure provided information on the date of spawning and early growth patterns
of all species sampled in the upper Mumumbidgee catchment. In addition to determining the
age and thus 'birth-date' of an individual, the effect of a particular event or series of events has
on growth, and subsequent survival, is permanently recorded in the otolith microstructure.
This enables accurate back-calculation and correlation to management actions or natural
events. No other research tool has this ability to retrospectively assess, on a daily basis, the
impacts of management actions on condition and subsequent survival of fish larvae.
Species sampled could be separated into three groups based on spawning requirements; those
linked with flow, those linked with temperature and generalist species that appear to have river
independent cues, such as photoperiod or moon phase.
Patterns in growth rate during the early life history stages enabled quantification of the
consequences of variation in environmental conditions on the survival and recruitment of
various species. Growth was not always highly correlated with water temperature, in fact, for
mountain galaxias, high temperatures appear to negatively affect larval condition and
subsequent survival. Conversely, carp exhibited a strategy more consistent with common
perceptions, with growth and survival increasing with increasing temperature.
The study uncovered spawning and growth patterns that were unexpected. Age analysis of
western carp gudgeon demonstrated that they had undertaken a mid-winter spawning, when
the water temperature in the main channel was far lower than that at which spawning was
previously recorded for this species. Redfin perch from the unregulated Goodradigbee River
exhibited growth rates exceeding the published upper limits for this and other closely related
species. This growth could not be correlated with either temperature or flow, indicating that
there are additional factors that dominate growth rates of redfin perch in the Goodradigbee
River.
The proportion and abundance of native species alone is not necessarily indicative of a
'healthy' or pristine system; some native species may be positively affected by river
regulation, at least as juveniles. Comparison of the current larval fish community with likely
pre-European fish communities does provide an indication of change to the system. The
results of this study suggest that larval fish growth rates can be strongly influenced by
environmental conditions, thus providing a powerful tool for monitoring future change and the
factors which cause it.
This study has demonstrated the value of larval and juvenile fish age and growth information,
derived from otolith microstructure techniques, for many aspects of river management.
Current river management priorities for which these techniques provide unique information
include the determination of environmental flow regimes and the control of undesirable exotic
species such as carp.
| Identifer | oai:union.ndltd.org:ADTP/218976 |
| Date | January 2003 |
| Creators | Peterson, Kylie, n/a |
| Publisher | University of Canberra. Resource, Environmental & Heritage Sciences |
| Source Sets | Australiasian Digital Theses Program |
| Language | English |
| Detected Language | English |
| Rights | ), Copyright Kylie Peterson |
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