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.

The National Carp Control Plan (NCCP), operating within the Fisheries Research and Development Corporation (FRDC), is developing a plan for the potential release of the virus known as Cyprinid herpesvirus 3 (CyHVto control invasive common carp, Cyprinus carpio, in Australian freshwater environments.
If the carp virus is approved for release, major carp mortality events are likely and the degradation of carp carcasses is likely to release a considerable amount of nutrients into the water column. Given the enormous biomass of carp in the Murray Darling Basin it is unlikely that this biomass will all be removed in a ‘clean-up’. Consequently, a strategy will be required to ensure this increase in nutrients does not become problematic. Of particular concern is ensuring that these nutrients do not fuel cyanobacterial blooms, which can compromise water quality by the production of toxins, and compounds that taint the taste and odour of water.

Preliminary work has been carried out at the University of Adelaide measuring the remobilisation rate of phosphorus from decaying carp tissue. This work needs to be expanded and incorporated into prediction of phytoplankton growth in the Murray Darling System to determine how this will support algal growth. Nutrients will interact with flow to determine phytoplankton abundance, species dominance and succession. The bloom forming cyanobacteria in the Murray Darling Basin tend to dominate under warm, stable stratified conditions. Consequently flow can be used as a strategy to ensure mixed conditions in the rivers and a greater likelihood that nutrients will be directed into phytoplankton species other than cyanobacteria.