Despite diligent monitoring, no signs of invading bass have showed up since the Arizona Game and Fish Department used chemicals to route invaders in the final two-mile stretch of Fossil Creek last year.
“We’ve continually done surveys in Fossil Creek since the renovation and we have not seen any smallmouth bass upstream of the barrier,” said Game and Fish Fisheries Branch Chief Chris Cantrell.
On the other hand, the populations of native fish appear to have fully recovered from the chemical treatments of the stream.
Smallmouth bass somehow got over a fish barrier intended to keep non-native fish in the Verde River from invading Fossil Creek, now one of the premier native fish refuges in the Southwest.
A flood piled up boulders and sediment on the downstream side of the fish barrier, allowing the bass to get past the barrier and swim upstream into the pristine waters of the spring-fed Fossil Creek.
Game and Fish biologists and volunteers had removed all the non-native fish from Fossil Creek more than five years ago before Arizona Public Service decommissioned a historic power plant and returned the water to the streambed. Game and Fish then returned to the resurrected creek some of the native fish species driven to the brink of extinction elsewhere by a combination of dams, water diversions and the introduction of non-native fish — like trout, catfish, bass and bluegill.
Trailhead parking limits
The Coconino National Forest this week imposed a weekend parking limit on the popular Fossil Springs Trailhead just outside of Strawberry. The area has room for 30 cars, but on Memorial Day weekend, 100 people parked there for the arduous hike down to the creek.
Rim Country Search and Rescue hauls injured and overwhelmed hikers out almost every weekend.
The reinvasion of the creek by the voracious bass at first went unnoticed for a while in 2010. But biologists monitoring the creek eventually glimpsed the predatory bass in the crystal clear pools. After a delay of almost six months as Game and Fish labored to cope with the Forest Service restrictions on construction projects in wilderness areas, Game and Fish repaired the fish barrier.
Then last September a six-man crew spent weeks netting perhaps 100 to 300 native fish to move upstream, before using a chemical to kill all the fish remaining in the final 2.5 miles of the stream before it merges with the Verde River.
The cost of “renovating” the stream topped $200,000, but biologists figured it offered the only hope of preventing the hungry bass from gobbling up most of the young, predatory headwater and roundtail chub within a couple of years, not to mention the desert suckers, Sonoran suckers, razorback suckers, longfin dace, spikedace, loachminnows and Gila topminnows.
The team spent weeks using nets and electroshock to remove the bass seen above the barrier. They spent hundreds of additional man-hours hiking and snorkeling upstream to look for any bass that had escaped. An official with the project said simply looking down into the pools remains the best way to spot the bass, which are clearly visible in water that remains so transparent you can see to the bottom of 20-foot-deep pools.
The crew put out about 100 fish traps, baiting with food used in hatcheries. They killed the bass they captured, but put the native fish in backpack buckets outfitted with battery-operated bubblers and hauled them out the 1.5 miles back to the road. The buckets could carry about 10 grown fish or about 20 small fish. In that manner, the crew moved as many as 300 native fish upstream above the bridge below the power plant site.
Crews used Rotenone to effectively suffocate the remaining gill-breathers. Laboratory tests have shown that the chemical can cause Parkinson’s-like symptoms in laboratory animals. However, the concentrations used to kill the fish in a stream remain far below those levels. The chemical breaks down quickly into harmless byproducts. In addition, the crews released a second chemical that neutralized any lingering traces once it had killed all the fish in that 2.5-mile stretch of stream.
The biologists got there just in time, since many of the bass they captured had already spawned.
Cantrell said no one has seen a trace of bass above the fish barrier since the project concluded.