Continental threat: How many common carp (Cyprinus carpio) are there in Australia?. (February 2021)

• Record Type: Journal Article
• Authors: Stuart, I.G.; Fanson, B.G.; Lyon, J.P.; Stocks, J.; Brooks, S.; Norris, A.; Thwaites, L.; Beitzel, M.; Hutchison, M.; Ye, Q.; Koehn, J.D.; Bennett, A.F.
• Is Part Of: Biological conservation. Volume 254(2021)
• Publication Date: 2021-02
• Subjects: Common carp -- Cyprinus carpio -- Invasive species -- Density -- Biomass -- Pest management; Conservation of natural resources -- Periodicals; Nature conservation -- Periodicals; Ecology -- Periodicals; Environment -- Periodicals; Environmental Pollution -- Periodicals; Electronic journals; 333.9516
• DOI: 10.1016/j.biocon.2020.108942
• Languages: English
• ISSNs: 0006-3207

Abstract

Abstract: Common carp ( Cyprinus carpio ) are one of the world's most destructive vertebrate pests. In Australia, they dominate many aquatic ecosystems causing a severe threat to aquatic plants, invertebrates, water quality, native fish and social amenity. The Australian Government is considering release of cyprinid herpesvirus-3 (CyHV-3) as a control measure and consequently a robust, continental-scale estimate of the carp population and biomass is essential to inform planning and risk management. Here, we pioneer a novel model-based approach to provide the first estimate of carp density (no/ha) and biomass density (kg/ha) at river reach/waterbody, basin and continental scales. We built a spatial layer of rivers and waterbodies, classified aquatic habitats and calculated the area of each throughout the range of carp in Australia. We then developed a database of fishery-independent electrofishing catch-per-unit-effort (CPUE) for habitat types, containing catch information for 574, 145 carp caught at 4831 sites. Eastern Australia accounted for 96% of carp biomass and 92% of the total available wetted habitat area (16, 686 km 2 ) was occupied. To correct these data for variable detection efficiencies, we used existing electrofishing data and undertook additional field experiments to establish relationships between relative and absolute abundances. We then scaled-up site-based estimates to habitat types to generate continental estimates. The number of carp was estimated at 199.2 M (95%Crl: 106 M to 357.6 M) for an 'average' hydrological scenario and 357.5 M (95%Crl: 178.9 M to 685.1 M) for a 'wet' hydrological scenario. In eastern Australia, these numbers correspond with biomasses of 205, 774 t (95%Crl: 117, 532–356, 482 t) (average scenario) and 368, 357 t (95%Crl: 184, 234–705, 630 t) (wet scenario). At a continental scale the total biomass was estimated at 215, 456 t for an 'average' hydrological scenario. Perennial lowland rivers had the highest CPUE and greatest biomass density (up to 826 kg/ha) and the modelled biomass exceeded a density-impact threshold of 80–100 kg/ha in 54% of wetlands and 97% of stream area in large lowland rivers. The continental-scale biomass estimates provide a baseline for focusing national conservation strategies to reduce carp populations below thresholds needed to restore aquatic ecosystems at a range of spatial scales. Graphical abstract: Distribution and predicted density of non-native common carp Cyprinus carpio on the Australian continent. Up to 96% of common carp occur in eastern Australia where the modelled numbers, for fish >150 mm long, fluctuated between 199.2 M (95%Crl: 106 M to 357.6 M) for an 'average' hydrological scenario and 357.6 M (95%Crl: 178.9 M to 685.1 M) for a 'wet' hydrological scenario. The biomass density (kg/ha) of common carp exceeded the accepted biodiversity-threat threshold of 80–100 kg/ha in 54% of wetlands, 70% of stream area for rivers, and 97% of stream area in large (>40 m wide) lowland rivers. Unlabelled Image Highlights: We collated data from 4831 sites to estimate Australia's carp population. Eastern Australia, accounted for 96% of carp biomass and 92% of aquatic habitat area was occupied. Estimated abundance is 199.2M and 215, 456 tonnes in an average hydrological scenario with higher numbers in a wet scenario. Carp exceed the threshold for biodiversity impact in 54% of wetlands, 70% of rivers and 97% of large lowland rivers. We provide a baseline for focusing management efforts and restoring aquatic ecosystems.