The lower Lachlan catchment provides a unique opportunity for
implementation of a carp (and other pest fish) control program in
the Murray-Darling Basin. Firstly, the density of carp in the
Lachlan catchment is one of the highest in any catchment in New
South Wales, and is probably one of the most abundant carp
populations in Australia. Secondly, the carp population in the
lower Lachlan is supported by two known and two other potential
carp recruitment hotspots: the Great Cumbungi Swamp, Lake Brewster,
Lake Cargelligo and Lake Cowal, each having features amenable to
trialling of control options. Thirdly (and most importantly),
the Lachlan is typically an endorheic system (largely isolated from
the remainder of the Murray-Darling Basin) and only ever connects
with the Murrumbidgee River during periods of exceptionally high
flow (1 in 20 year floods). As a result, the carp population
within the Lower Lachlan catchment is not exposed to continual
immigration from carp populations in other catchments.
The initial two years of this project are focusing on
benchmarking the status of the carp population and the aquatic
ecosystem in the lower catchment. Benchmarks are being established
for the size of the carp population, relative level of carp
recruitment from each hotspot, and the status of water quality
parameters, riverbank stability, aquatic vegetation cover,
macro-invertebrate and native fish community composition and social
attitudes towards carp.
A number of replicate carp exclosures are also
being established to quantify the impact of carp on aquatic
vegetation (as well as macro-invertebrates and native fish)and the
expected rate of ecosystem recovery. This aspect of the
project will also provide a visible focal point for demonstration
of the outcomes of carp control to the community.
A large number of carp will be tagged and released to enable
mark-recapture estimates of population size so that the
effectiveness of subsequent carp removal activities can be gauged
on the proportion of the population removed.
Carp removal activities implemented from year
three onwards (the implementation phase) will be focused on the
recruitment hotspots and include:
- exclusion of adult carp from hotspot locations
- trapping of carp dispersing from hotspot locations
- removal of migrating carp in riverine fishway traps
- removal of carp from freshwater lakes using
attractants/traps
- commercial harvest from freshwater lakes
- recreational harvest through community based carp fish-out
competitions and general recreational fishing activities
- the implementation of daughterless carp gene technology when/if
it becomes available for field application, and
- any other control options provided through the freshwater
products and strategies program as they become available.
Progress update:
Carp tagging continued through
October to December, with 1,579 tagged carp in the Lachlan at the
end of December. Of these, 12 had been recaptured by recreational
fishers and 16 by project officers during electrofishing
operations.
Construction of three exclosure
cages has begun. Two sites have been selected as suitable for
installation of the cages with a third site yet to be chosen.
Aerial mapping of the Lake
Cowal/Bland Creek sub-catchment was completed in November. The
exercise determined that 219.36 km of waterway contained water (10%
of the stream network) consisting of 145 isolated remnant
waterholes. The next step is to contact relevant landowners to
determine whether these ‘wetted’ habitats have dried
out completely at any time during the past few years. If the number
of separated wetted habitats that have remained wet throughout the
drought is reasonably finite, carp eradication attempts in the
sub-catchment are very feasible.
A team of project participants
led by SARDI trialled carp traps within the inlet and outlet
channels at Lake Brewster, the inlet channel to Lake Cargelligo and
in the Great Cumbung Swamp in October. The team included staff from
SARDI, the Lachlan CMA, State Water, K & C Fisheries,
Kingfisher Research and NSW DPI.
124 young-of-year carp were
sampled from potential hotspot locations in November. These fish
will be used to quantify the otolith microchemical signatures of
each potential hotspot for subsequent assessment of the relative
importance of each hotspot for recruitment into the carp population
of the lower Lachlan catchment as a whole.
Project collaborators:
NSW Department of Primary Industries (NSW
DPI)
South Australian Research and Development
Institute (SARDI)
Victorian Department of Sustainability and the Environment
(VIC DSE)
Lachlan Catchment Management Authority (LCMA)
State Water Corporation
K. & C. Fisheries Global Pty Ltd
Kingfisher Research Pty Ltd
