Managing invasive carp (Cyprinus carpio L.) for habitat enhancement at Botany Wetlands, Australia

Abstract

Abstract In Australia, the carp Cyprinus carpio L. is regarded as a threat to the native fish and the aquatic environment. In recent years, Botany Wetlands, a significant coastal wetland in the Sydney region, has been invaded by the undesirable cyprinids, carp and goldfish (Carrasius auratus L.). In 1996 a cyprinid removal programme commenced at Botany Wetlands with the objective of managing the invasive species, increasing fish diversity, reducing cyanobacterial blooms and hence enhancing the aquatic habitat. Using electrofishing and gill netting, 4073 carp and 261 goldfish, amounting to 10 117 kg of cyprinid biomass were removed between 1996 and 2004. The captured carp ranged from 60 to 835 mm. Males matured before females. Carp between 350 and 680 mm in length grew at the rate of 1.66±0.38 g day−1. The success of the programme was monitored by assessing four indicators related to carp populations and two related to habitat. The former included the pattern of length–frequency distribution, mean weight per size class, condition factor (CF) and the catch per unit effort (CPUE), and the latter the Secchi disc transparency and cyanobacterial counts. After 8 yr of removal, the plots of carp length–frequency distribution flattened, CF decreased from 2.86 to 1.82 and CPUE decreased from 97 kg day−1 to 50 kg day−1. A 10‐fold decrease occurred in cyanobacterial counts and the Secchi disc transparency increased by 20%. More than 20 000 fingerlings of native Australian bass Macquaria novemaculeata (S.) have been introduced to the wetlands, increasing the potential for juvenile carp predation and biodiversity. Copyright © 2005 John Wiley & Sons, Ltd.