FRDC is leading a National Carp Control Plan (NCCP) to ensure maximum success of the CyHV-3 virus. The objective of the present proposal is to inform resource allocation for CyHV-3 release planning, clean-up and management of potential ecological impacts, and provide a robust estimate of carp abundance and biomass in a broad range of aquatic habitats, reaches and river basins in eastern Australia. As part of this program it is underrating an assessment of Carp biomasses (NCCP: Preparing for carp herpesvirus: a carp biomass estimate for eastern Australia) based on data collected at various points in time.
Carp are highly fecund and adaptable and therefore their populations are extremely dynamic. This means that any static population estimate at any particular point in time can quickly change, and therefore must be used cautiously. It also means that overall populations can vary widely: data from river surveys in the mid-Murray (relatively stable habitats) varied by about 200% pre-, during and post drought. Less stable habitats would be likely to have higher levels of population variability. By their very nature, population assessments can only be undertaken at individual sites at particular points in time and there is the need for adjustments to this data to provide more accurate estimates of populations for any other point in time.
Carp population dynamics are driven by very large recruitment events and there are three factors that influence recruitment events:
1. flows (hydrology); and
2. access to habitats (often also dictated by flows)
3. existing population structure
Carp populations are particularly responsive to conditions conducive to recruitment, especially when there are successive events that cumulatively drive populations. Therefore, these aspects need to be taken into account to guide management and allow predictions to be made as to actions and likely outcomes. The carp biomass estimate currently being undertaken will give a point-in-time estimate for July 2018. This will need to be adjusted for any release date beyond 2018. Data collected should allow for examination of the existing population structure, which can then be added into the model for future predictions.
This study was undertaken by the Arthur Rylah Institute for the Department of Environment, Land, Water and Planning. Carp (Cyprinus carpio) is Australia’s most invasive pest fish. To facilitate more effective management, the Australian Government is considering release of a Carp herpesvirus (CyHV-3) (‘Carp virus’), as a potential biological control agent. This required an estimation of Carp biomass across Australia. This Carp biomass estimate provided static ‘points-in-time’ (for May 2011 and May 2018) derived from available historic catch data collected over the past 20-years. As Carp populations can respond rapidly to hydrological conditions, especially flood events that provide access to preferred spawning habitats and can lead to significant recruitment, there is a need to consider likely population outcomes from subsequent hydrological conditions. Multiple wet years can lead to large population growth and multiple dry years leading to population stagnation or decline. Hence, the static 2011 and 2018 biomass estimates cannot specifically be applied to future scenarios when the Carp virus may be released. The use of a dynamic Carp population model was recognised as a method that could provide future estimates of biomass, taking into account likely several possible hydrological scenarios for the time of future virus release. The aim of this project was to modify and apply the existing Carp population model to provide forward temporal estimates of likely Carp biomass and numbers for a range of hydrological scenarios for the year 2023, using the static estimate for 2018 provided from the Carp biomass project.