Invasive Species Compendium

Detailed coverage of invasive species threatening livelihoods and the environment worldwide

Abstract

Rotenone policy support and capacity development. Part 1: Impact and recovery of biota in one river and two dams following alien fish removals using rotenone.

Abstract

This technical report aims to: (i) provide data on ecosystem responses of one river and two dams following Rotenone treatment to guide national policy on the use of Rotenone for non-native fish removals; (ii) monitor rates of recovery of fish communities in the Rondegat River continuously to determine when complete recovery has occurred by testing the hypothesis that native fish communities rebuild to approximate those in the non-invaded zone of the river within 5 years after the first treatment; and (iii) assess the recruitment and recovery rates of invertebrate communities to the removal of alien fishes using Rotenone in two off-channel dams. The findings of the long-term monitoring included: (i) no smallmouth bass have been detected following the Rotenone treatment and it is considered to have been successful. (ii) Native fish rapidly colonised the reach where smallmouth bass had been eradicated. The densities of the three cyprinid species in the rehabilitated area are beginning to resemble those in the control area. (iii) A catastrophic invertebrate-drift event occurred during the application of Rotenone to the Rondegat River. The effect was immediate, with the number of invertebrates in the drift climbing two orders of magnitude above natural background drift levels, which remained constant at the monitoring site in the control area throughout the Rotenone treatment. Following the end of Rotenone treatment, drift rapidly declined to near-pre-treatment levels. (iv) Stone and kick sampling of aquatic invertebrates were conducted to quantitatively sample invertebrates such that the impact of the Rotenone treatment on invertebrates could be made based on quantitative assessments of species numbers and diversity. (v) Results from assessments based on the most sensitive taxa, commonly referred to as EPT (Ephemeroptera, Plecoptera and Trichoptera) demonstrated a rapid recovery following treatments.