Fish and Game to monitor impacts to fisheries from quagga mussel treatment

Quagga mussels have once again been detected in the Snake River near Twin Falls. The new detections were a result of extensive proactive monitoring done by the Idaho State Department of Agriculture (ISDA), the state agency responsible for invasive species monitoring and management. 

While ISDA detected fewer mussels in 2024 than in 2023, the second treatment to eradicate mussels is a critical step to stop further spread.

ISDA began the 2024 chelated copper treatment on Tuesday, October 8, 2024. 

Using experience gained from the 2023 treatment, Fish and Game fisheries biologists are preparing for additional fish mortality throughout the treatment area, especially in the section of river upstream of the Twin Falls power plant that was not treated in 2023. 

Pre-treatment surveys 

Prior to the treatment, Fish and Game fisheries biologists have conducted pre-treatment surveys in the river, upstream of the Twin Falls power plant, to collect fish community composition and biological data within the reservoir section of the new treatment area. 

These data will also allow the department to determine the success of fisheries recovery efforts in the future.

Similar pre-treatment surveys were conducted in 2023 both in and outside the treatment area of the Snake River.

White sturgeon mortality

White sturgeon are not native upstream of Shoshone Falls and have not been previously stocked within the new treatment portion of the river. It is possible for white sturgeon to move downstream from other stocked locations, so, white sturgeon mortality is possible but unlikely. 

The Department is not expecting much additional white sturgeon mortality within the 2023 treatment section of the Snake River. It is assumed that white sturgeon mortality approached 100% during the 2023 chelated copper treatment. 

Since the 2023 treatment, no white sturgeon were released or translocated in the reach between Pillar Falls and Centennial Park, so biologists do not expect much, if any, additional white sturgeon mortalities associated with the 2024 treatment within the lower reach.