Fossil Creek Bass Pose Threat

Game and Fish may use chemicals to kill non-native fish

Small mouth bass


Small mouth bass


Arizona Game and Fish officials think they rounded up most of the non-native smallmouth bass that have invaded the native fish refuge of Fossil Creek — but they’re not absolutely sure.

As a result, the Game and Fish Department is now considering a plan to use a fish-killing chemical to remove non-native fish from the lower reaches of the travertine-tinted, spring-fed creek.

“We’ve pretty thoroughly surveyed all the pools, to the point of exhaustion for the people doing it,” said Game and Fish Fisheries Branch Manager Kirk Young. “We’re working through the process of deciding whether to use Rotenone right now — but obviously Fossil Creek is a very high priority for us.”

The current closure of Fossil Creek may provide the perfect opportunity to “renovate” the stream and remove any bass or other non-native fish that might have gotten past both permanent and temporary fish barriers after a flood left a pile of sand and boulders on the downstream side of the fish barrier installed five years ago. The barriers were intended to keep bass, catfish, sunfish and other non-native fish from moving from the Verde River up into Fossil Creek. Game and Fish undertook an expensive project to remove all the non-native fish from Fossil Creek about five years ago before the removal of a hydroelectric plant returned the water to the streambed.

The creek flows for 16 miles from a gushing spring to its junction with the Verde River and deposits an estimated 13 tons of travertine along its bed every day. The stream now harbors one of the best refuges for native fish in the state, with two types of chub, two types of suckers and several smaller fish thriving there, with a diversity of native fish rivaled only by little Aravaipa Creek in southeastern Arizona and the Little Colorado River deep in the Grand Canyon.

Young said crews removed about a dozen bass from several locations, using a combination of electro shocking, netting and fishing. At least one bass the crews spotted escaped, although Young speculated that the bass might have died anyway due to the repeated exposure to an electrical current that normally stuns fish.

Young said he still doesn’t know whether the bass found came upstream from the Verde River around the compromised fish barriers or whether someone planted the non-native fish above the barrier. He said he also doesn’t know for sure how long the bass had been living above the barrier — and whether any managed to lay eggs before the roundup.

As a result, Game and Fish may decide to remove native fish and then use Rotenone to kill any remaining fish in several miles of stream above the now-repaired fish barrier.


Arizona Game and Fish officials are in the process of trying to rid Fossil Creek of the smallmouth bass that threaten the endangered, native fish living in the spring-fed creek.

The Arizona Game and Fish Department has just lifted a self-imposed moratorium on the use of the fish-killing chemical made from a substance found in the roots of plants that can prevent fish from absorbing oxygen through their gills. After animal tests showed that the chemical can cause Parkinson’s-like symptoms in lab animals at extremely high doses, the manufacturer curtailed all uses except for killing fish in ponds and streams. Those concentrations far exceed human exposures, but the Environmental Protection Agency (EPA) concluded it didn’t have good enough data to set firm maximum exposure limit in humans. As a result, the adopted standard is about 10 times more restrictive than the lab animal tests suggested is necessary.

Game and Fish set up a panel of experts to review use of the chemical. They came out with a new set of rules based on guidelines issued by the EPA. The EPA set concentration limits based on the finding that the chemical breaks down quickly, doesn’t accumulate in the tissues of fish or other animals and isn’t readily absorbed through the skin.

The Game and Fish Committee adopted those standards and added the need for additional assessments any time the use of the chemical might affect groundwater or drinking water, as it could along a stream like the East Verde where wells supplying subdivisions are most likely directly connected to the stream flow.

Fossil Creek flows down a deep canyon, with no connection to any drinking water supplies until after it flows into the Verde River.

The appearance of the bass above the fish barrier has posed an alarming threat to the native fish that now populate every crystal-clear pool along the creek.

Last year fish biologists discovered a flood had piled up rocks and sand below the fish barrier. Shortly after that, biologists spotted several small bass in several different pools just upstream from that first barrier.

Game and Fish built another temporary barrier about 1.5 miles upstream to keep those bass from spreading, while they worked through federal wilderness restrictions to get permission to repair the original barrier.

Then in April, biologists discovered nine bass about two miles upstream from the temporary barrier. The biologists captured eight of those bass, but at least three escaped.

They returned several weeks later to conduct a survey both upstream and downstream from that pool and captured one additional bass.

“These bass were just hanging out — they weren’t making any effort to hide, so they were pretty easy to see.”

They surveyed all the way down to the temporary barrier as well as a shorter distance upstream, said Young.

Game and Fish hopes to team up with some university researchers to run tests on the bass they removed to see if the chemical isotopes in their scales might reveal where they came from. “If they came from the Verde River, they would have an isotope signature similar to the fish in there now. If they came from somewhere else — Minnesota, Roosevelt Lake, wherever — the isotope might tell us.”

Game and Fish has established a unique, fall fishery to let catch-and-release anglers with barbless hooks try to catch some of the creek’s 20,000 headwater and roundtail chub. The stream also now harbors sonoran suckers, desert suckers, razorback suckers, longfin dace, spikedace, loachminnow and Gila gopminnow’s — almost all of them either threatened or endangered species.


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