Bass invaded Fossil Creek sometime last year when flood waters caused a breach of the barrier intended to keep non-native fish out of the pristine stream.
Photo by Pete Aleshire.
The Arizona Department of Game and Fish in September will use a fish-killing poison to kill non-native bass that have invaded about 2.6 miles of Fossil Creek — perhaps the premier native fish refuge in the state.
Game and Fish and the U.S. Fish and Wildlife Service will hold a public hearing in Camp Verde on Aug. 29 starting at 5 p.m. to get public reaction on plans to use the chemical rotenone in the stretch of the creek upstream from its junction with the Verde River.
“The whole point of the meeting is to advise the public of the proposed treatment of a portion of Fossil Creek,” said Game and Fish Program Manager Scott Rogers. “We will have representatives there providing information about the proposed treatment, length of time it will take and answer questions the public may have.”
The bass invaded the clear, travertine-tinted, spring-fed stream sometime last year, when flood waters left sand and boulders piled up on the downstream side of a fish barrier intended to keep bass, catfish, carp and other non-native fish out of the pristine stream.
Game and Fish employees discovered bass a short distance above the breached barrier last year. That triggered a request to the U.S. Forest Service for permission to build a temporary fish barrier upstream until Game and Fish and the U.S. Fish and Wildlife Service could repair the main barrier. However, the Forest Service enforced rules against using heavy equipment in a wildness area, which delayed the installation of the second temporary barrier by several months.
Subsequently, biologists discovered about a dozen bass more than a mile above the temporary barrier. They caught most of those bass, but several vanished.
“The whole point of the meeting is to advise the public of the proposed treatment of a portion of Fossil Creek.”
Game and Fish Program Manager
All that led to the current proposal to use a plant-derived poison that suffocates any creatures that breathe through gills.
Game and Fish had for more than a year suspended use of rotenone, the most common chemical used to kill off fish in a stream. Several studies had raised questions about how fast the chemical dissipated, especially when used in streams that provide drinking water. Fossil Creek empties into the Verde River, which runs downstream into reservoirs that provide drinking water to Phoenix. However, the chemical typically dissipates quickly.
Game and Fish lifted the moratorium on use of rotenone after a scientific committee came up with upgraded guidelines for its use.
Game and Fish biologists recommended the effort to kill any non-native fish that have invaded the lower reaches of the creek to protect one of the premier refuges for native fish in the southwest.
The spring-fed flow of Fossil Creek was for a century diverted down a flume to spin the turbines on a hydro-electric power plant, which helped feed the electrical needs of Phoenix in the 20th Century. However, Arizona Public Service seven years ago agreed to decommission the power plant and return the flow of the creek to the streambed.
Game and Fish used electro-shocking to remove as many native fish in the creek as possible, including headwater and roundtail chub, sonoran suckers, several minnow-like dace and others. Most of those fish are endangered as a result of a century of dams and diversions that have transformed almost every stream and river in the southwest.
Biologists killed off all the non-native fish like catfish, bass, red shiners, carp and others that had come to dominate the stream, before finally returning both the native fish they had removed and the full flow of the spring to the creekbed.
The native fish have thrived in the deep, crystal clear pools of the resurrected stream. An estimated 20,000 headwater chub alone now live in the creek, with large populations of half a dozen other native fish.
The invasion of the voracious smallmouth bass and any other fish that managed to surmount the damaged fish barrier could threaten a rare native fish success triumph.