Young-of-year common carp (Cyprinus carpio) nursery sources in and around Koondrook-Perricoota Forest following 2016 flood
Duncan, M., Martin, K., Rogers, T. and Gillanders, B., 2017. Young-of-year common carp (Cyprinus carpio) nursery sources in and around Koondrook-Perricoota Forest following 2016 flood. Report to Forestry Corporation and Murray-Darling Basin Authority, 30p.
Koondrook–Perricoota Forest (KPF) is located on the Murray River floodplain upstream of Barham in NSW. It spans approximately 33,000 hectares and is one of six Living Murray icon sites due to its significant wetland and creek ecosystems. These ecosystems are highly reliant on floodwaters with flooding being historically more common than under current regulated conditions. Recently, a range of environmental works and measures have been completed that enable the KPF to be flooded without the need for an overbank flow. This can potentially have a range of positive and negative outcomes for fish populations (and for other environmental values such as the River Red Gum community in the forest). The creation of shallow wetland habitat may provide ideal spawning conditions for native small-bodied fish. Similar conditions are also favoured by the introduced common carp and there is a risk that inundating a large area of wetland and creek habitat will allow common carp to successfully spawn and recruit. Consequently, KPF could potentially act as a major source population of common carp that could colonise the Murray River following environmental watering.
An earlier study calculated the ages of young-of-year carp collected in KPF following a managed flood event in 2014 and determined that they were from reproductive events that occurred within the forest after connectivity to the Murray River was lost. Here we expand on that work and use otolith (ear bones) chemistry to determine if common carp originating from KPF colonised the Murray River as young-of-year (YOY) fish following a natural flood in 2016. Larval fish were sampled from within KPF and in the surrounding rivers in order to determine if the forest had a unique chemical signature that differentiated it from other areas. Young-of-year carp were sampled during autumn 2017 and the chemical signature from near the core of their otoliths was matched to the larval chemical signatures in order to estimate where they were spawned using discriminant-based analysis. Results clearly showed that common carp YOY collected in the Murray River did not originate from reproductive events in KPF. Furthermore, only a single YOY collected inside KPF originated from KPF, all others originated from natal locations outside of the forest. The findings of this study strongly suggest that the larval carp within the KPF had a very poor survival rate, most likely due to acidic and anoxic water associated with the flood. Combined results from the 2014 work and this study suggest that regular small-scale managed floods that do not inundate large areas of leaf litter may result in more successful recruitment of common carp than much larger floods that inundate areas that have been dry for several years.