Dissolved Oxygen Depletion for Invasive Fish Eradication

Authors: David Ward, Shaula Hedwall

Year: 2024

Abstract

Sodium sulfite is a powerful oxygen scavenger that is used to preserve meat and dried fruit and is generally recognized as safe by the EPA. It can also be used to remove oxygen out of a pond or stream, causing fish to come to the surface. We conducted 3 experimental treatments in 2024 to evaluate sodium sulfite as a fish management tool. Bulkhead Cove (0.8 hectare pond in California) adjacent to Lake Havasu, Piute Springs (0.4 cfs stream section) of the Little Colorado River, on the Navajo Nation, and pools (non-flowing) within Leonard Canyon immediately below Knoll Lake Dam, AZ were all treated with sodium sulfite to remove invasive fishes. Sodium sulfite dispensed at 0.16 g/L decreased dissolved oxygen to zero in less than 30 minutes in all treatments causing fish to gulp at the surface and allowing them to be captured with a hand net. Non-native green sunfish (Lepomis cyanellus), common carp (Cyprinus carpio), black bullhead (Ictalurus melas), channel catfish (Ictalurus punctatus), and fathead minnow (Pimephales promelas) were all killed while native speckled dace (Rhinichthys osculus) and humpback chub (Gila cypha) were able to be captured and revived in fresh water. Oxygen depletion may have advantages over other fish removal methods in that water quality conditions quickly return to pre-treatment conditions (a few hours to several days, depending on dosing) with no harmful residues and minimal impact to non-target species or the environment. Salinity increased by 0.1 ppt and sulfates increased by approximately 50 mg/l above baseline conditions in each treatment. In each case, water remained within drinking water standards during and following fish removal! Additional tools for control of invasive aquatic species are sorely needed and although this tool may only be effective in small ponds and streams, the addition of any new tool for invasive fish management is helpful in the ongoing battle to prevent extinction of southwestern native fishes. Moving from experimental use to a licensed and registered piscicide appears possible but will only be achievable with significant support from regulatory and wildlife management agencies.