Smallmouth bass have invaded the lower reaches of Fossil Creek, posing an acute new danger to efforts to make the travertine-rich, spring-fed creek a refuge for dwindling native fish.
This summer, Coconino National Forest officials noted dozens of bass lazing about in pools upstream from concrete fish barriers intended to keep non-native predatory fish found in the Verde River from swimming upstream into Fossil Creek.
State and federal wildlife agencies spent millions of dollars getting rid of non-native fish that once dominated Fossil Creek.
The creek has become one of the most healthy and diverse refuges of native fish since the return of the full flow of the spring to the creek five years after the decommissioning of a century-old hydro-electric plant.
Biologists laboriously electro-shocked, collected and moved into tanks native fish like the Sonoran sucker, headwater chub and Verde chub. Then they poisoned the remaining pools to get rid of species like bass, catfish and sunfish — introduced fish that dominate almost every other stream and river stretch in Arizona.
Crews built a concrete fish barrier near where Fossil Creek empties into the Verde River, in hopes of keeping the non-native fish out.
The summer’s discovery suggests that tactic failed.
The discovery of dozens of small bass in pools 300 feet upstream from the barrier prompted additional searches.
Biologists with the Arizona Game and Fish Department found smaller numbers of bass as much as a half mile upstream from the fish barrier.
Biologists speculate that a 2010 flood lodged several large boulders up against the fish barrier, then deposited sediment up against the downstream side of the barrier. That might have allowed ambitious bass to jump the barrier.
The fish barrier lies in a wilderness area, which complicated efforts to get equipment into the site to remove the boulders. A preliminary effort to remove the rocks floundered this summer, so crews installed a new, temporary fish barrier upstream from the existing structure.
U.S. Bureau of Reclamation officials said that they probably won’t repair the existing barrier and get additional barriers in place until sometime next year.
Once crews complete the barriers, biologists may have to once again remove the native fish and poison out the remaining non-native fish in that lower reach of the river to again safeguard the booming native fishery.
The U.S. Forest Service, meanwhile, continues to work on a master plan for development of the creek, which attempts to balance recreation with the needs of the wildlife — especially native fish.
Preliminary plans call for limiting access to the stream during the summer, when thousands of people crowd into the canyon and splash about in deep, crystal clear pools swarming with native fish.
The Forest Service would ban parking during peak periods and instead contract for a shuttle bus to get people down into the canyon.
The plan mostly emphasizes recreation, on the assumption that the weekend swarms of humans along the stretch of road-accessible stream won’t harm the native fish and other endangered species making a recovery in the resurrected creek, like the Chiricahua leopard frog.
Up until now, the native fish have done so well in Fossil Creek that the Arizona Game and Fish Department has experimented with a catch-and-release fishery, which allows anglers to fish for the native fish that dart about in every major pool.
Fish like the headwater chub and the roundtail chub, also known as the Verde trout, once wriggled through most of the lower-elevation streams in Arizona, including the Colorado River.
Ideally adapted to the flood-prone, warm, muddy, fickle nature of Arizona streams and rivers, many had lifestyles that ranged from small tributaries to the headwaters of the Colorado River.
Historical accounts suggest the native fish teemed in the Salt and Verde rivers in such numbers that early farmers would pitchfork them out of irrigation ditches to serve as fertilizer on their crops.
A century of dams, water diversions and competition from voracious introduced fish and other invaders like crayfish and bullfrogs has driven the native fish from most of their former haunts and on the road to extinction.
Bass and trout are skilled and aggressive predators, who are generally involved in systems that have a much greater diversity of fish and rougher competition for food. In many cases, they breed at different times of the year from the native fish so that their youngsters gobble up the eggs and emerging fry of the native fish.
Moreover, reservoirs that contain floods and release cold, clear water off the bottom of great lakes has put the flood-adapted native species at a great disadvantage against predators like bass and trout.
Many of the native fish have thrived in Fossil Creek since the