Northern pike (Esox lucius) are a nonnative invasive fish species that threaten California’s aquatic resources. California has been working to eradicate the fish from Lake Davis.
After a recent successful treatment of the creeks flowing into Lake Davis, the California Department of Fish and Game plans to begin a second stream treatment on Monday, Sept 24. The reservoir treatment is scheduled for Tues Sept 25 and Wed Sept 26. The reservoir is anticipated to be at 41,000 to 42,000 acre-feet at that time. The project uses a liquid rotenone formulation, CFT Legumine.
Releases from the dam into Big Grizzly Creek will be shut off for five days when the reservoir treatment begins. Current plans call for the dam to remain closed for up to 45 days to allow the rotenone formulation compounds to degrade naturally in the reservoir. One day recently, DFG crews netted about 200 trout in Big Grizzly Creek immediately below the dam and moved them further down the creek where incoming springs will provide sufficient habitat after flow from the dam is shut off. About half the fish were 8 inches or larger in size, and about two thirds were brown trout, and the remainder rainbow.
After the first treatment in the creeks upstream of Lake Davis, several hundred dead pike were observed - mostly young-of-the year, one-year-old fish, and a few 2-year olds. In some areas, pike were the only fish found – demonstrating how pike can dominate an ecosystem. This summer, DFG field crews did intensive electrofishing in the creeks to reduce the numbers of pike and help keep them from spreading further up the streams. Nearly two thousand pike were removed by that control method.
Northern pike are top predators with long torpedo shaped bodies built for speed. Their camouflaged coloration enables them to hide in aquatic vegetation and ambush their prey. Once a pike is about 8 inches long, it primarily feeds on other fish which it grasps in its wide mouth. Pike are also highly fecund; for each pound body weight, a female can lay 10,000 eggs.
The dead fish pose no danger to wildlife, such as herons and coyote, which are scavenging in the area. The water is safe for wildlife to drink.
The stream treatments are carried out using 5-gallon drip stations in flowing water, while crews using backpack sprayers and trailer-mounted spray rigs treated standing water and backwater areas. Screens are placed at the mouths of the tributaries to prevent any pike from re-entering the creeks.
Post-treatment stocking will begin when Lake Davis is free of any of the rotenone formulation compounds, which is anticipated to occur before the reservoir freezes over.
The majority of the stocking will occur in Spring 2008, with several hundred thousand fingerling, sub-catchable, catchable, and bonus size rainbow trout, along with fingerling brown trout.
In addition to the information provided in the EIR/EIS for the project, an analysis of the seven lots of rotenone being used in the project has been conducted.
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