A simple model for predicting ecological impacts of introduced aquatic organisms: a case study of common carp, Cyprinus carpio L., in the Sepik‐Ramu River Basin, Papua New Guinea

Practical models for predicting the impacts of introduced biota are urgently required to assess the benefits and risks of introductions. The simple method described predicts the ecological consequences of an introduction through potential competition between species based on elementary niche classifications. The model's predictions are tested against field data for common carp, Cyprinus carpio L., which escaped from fish farms during a study of the feasibility of fish stock enhancement in a large river basin. Recorded effects of carp are based on pre‐ and post‐carp gillnet catches, observations of local villagers, socio‐economic censuses and other sources of data. The predicted ecological interactions of common carp are in broad agreement with those recorded. The method can assist pre‐introduction assessments and is particularly useful where limited data exist. In this particular study, common carp have contributed significantly to an improved capture fishery by fortuitous accident; production from aquaculture was negligible. High niche overlap between carp and certain resident fish species is predicted and this may be of more consequence in highland than lowland regions. Organisms introduced/transferred for aquaculture should be assessed within a much wider forum. The intended impacts of an introduction/ transfer, which in the case study were entirely erroneous, is an area in need of considerable attention.