Forgotten Secrets of Invasive Fish Eradication

Authors: David Ward

Year: 2018

Abstract

Prior to the widespread use of rotenone as a tool for eradication of invasive fishes, extensive research was conducted on other chemical methods for removal of aquatic nuisance species. Most of this 1950’s to 1960’s research was quickly forgotten by biologists and managers as rotenone became the tool of choice for use in fish renovation projects. I evaluated two of these forgotten methods (pH manipulation using soda ash and oxygen depletion using sodium sulfite) for their effectiveness at eradicating invasive Green Sunfish, Lepomis cyanellus. Effective dosages for both chemicals were quantified in the laboratory followed by field trials conducted in two small research ponds. Soda ash was dispensed at 0.95 g/L to rapidly increase pH to >10.5. This sudden change in pH was effective at removing all Green Sunfish from two small ponds with pH returning to baseline conditions within 4 days. Sodium sulfite dispensed at 0.8 g/L rapidly decreased dissolved oxygen to < 1 mg/L causing fish to gulp at the surface and allowing them to be captured with a hand net. These tools may have advantages over other fish removal methods in that water quality conditions quickly return to baseline conditions (<48 hours for sodium sulfite and <96 hours for soda ash) with no harmful residues or other negative environmental impacts. Additional tools for control of invasive aquatic species are sorely needed and although these particular tools may only be effective in small isolated bodies of water, the addition of any new tool for invasive fish management is helpful in the ongoing battle to prevent extinctions of southwestern native fishes.