Ammonia as a tool for removal of invasive crayfish

Authors: Susan Wood, David Ward

Year: 2022

Abstract

Among the most destructive of aquatic invasives are multiple species of crayfish, several of which have been introduced globally. Across the southwestern US, introduced crayfish have negatively impacted native species due to their opportunistic feeding habits and ability to travel between isolated aquatic systems. Efforts to manually remove crayfish from invaded habitats have met with limited success. With increasing numbers of invasive species in aquatic systems comes a growing need for additional removal methods. The use of ammonia has shown promise as an alternative chemical removal technique for invasive fish. An ammonia-based tool could be a cost-effective way to eradicate invasive crayfish and support conservation of native aquatic species while utilizing natural nitrogen cycling to return an ecosystem to baseline conditions. To evaluate the use of ammonia as a tool for controlling invasive crayfish, specifically Northern Crayfish (Faxonius virilis) and Red Swamp Crayfish (Procambarus clarkii), we have used laboratory experiments to quantify lethal concentrations. Preliminary trials indicate that doses lethal to fish (21mg/l Total Ammonia Nitrogen (TAN) at a pH over 8) are ineffective in causing mortality for F. virilis. Concentrations approaching 50 mg/l TAN at a pH over 9.5 will kill crayfish if dissolved oxygen levels are also lowered using sodium sulfite. This combination of ammonium sulfate, sodium sulfite, and sodium carbonate to increase pH, achieves 100% mortality of F. virilis in 24 hours in a laboratory setting. Additional laboratory trials with P. clarkii, as well as field trials for both species, will be conducted to further investigate the potential for ammonia as a crayfish removal and management tool.