Population dynamics of invading freshwater fish: Common carp (Cyprinus carpio) in the Murray-Darling Basin, Australia

There is much interest in managing invasive freshwater fish, but little is known about the dynamics of these populations following establishment. We used annual commercial catch-per-unit-effort data at multiple spatio-temporal scales to test hypotheses about the population dynamics of invading common carp (Cyprinus carpio) in the Murray-Darling Basin, Australia. We hypothesised that following establishment of the Boolara strain of this species in the Murray-Darling Basin in 1961/1962: (1) carp would undergo exponential or logistic-type population growth; and (2) carp population growth rates would be highest following over-bank flood events that provided extensive off-channel spawning and feeding habitats. The logistic (w_i = 0.73) and delayed-logistic (w_i = 0.27) models best explained the population dynamics of common carp in the Murray-Darling Basin during 1962/1963-2001/2002; there was negligible support for exponential growth (w_i ≤ 0.01). Although we cannot exclude the possibility that floods may have been important in the early years of the invasion we found little evidence that carp population growth rates increased following flood events. Our logistic-type model-based estimates of the maximum annual population growth rate (r_m; 0.378 and 0.384) indicate that >0.315 or 0.319 of the adult population would need to be removed annually to achieve eradication. We conclude that the rapid spread of the Boolara strain of common carp through the Murray-Darling Basin was facilitated by high initial population growth rates. More generally, we suggest that the lag period between an invader establishing and increasing to high abundances will be characterised by logistic-type population growth. We encourage others to investigate the long-term population dynamics of invading freshwater fish using time series and models such as those reported here.