Biologists see a unique opportunity to re-intro endangered species to the Verde (Web only feature)

“Stocking razorback suckers in Stillman Lake is not going to make pumping the Big Chino go away,” said David Weedman, Aquatic Habitat Coordinator for Arizona Game & Fish Department.

Don't you love it when a biologist speaks in absolutes? Of course, he was speaking about human behavior, not about what the fish might do, but still, it's a lot different than the noncommittal “our research shows” or “based on historical evidence” or “the data indicate” that we usually hear from scientists. Refreshing.

Weedman's absolute came at the Monday, March 26 public meeting hosted by AZG&F and US Fish & Wildlife Service to explain their proposed project to remove non-native species from Stillman Lake and introduce natives like the endangered razorback sucker and the Verde trout, a “species of concern” on the edge of the endangered species list.

Stillman Lake, about 20 acres in size and no more than 10 feet at its deepest, is located at the confluence of Granite Creek and the very upper end of the Verde River. The lake, in fact, is actually within the riverbed and is the first navigable water on the Verde; Sullivan Lake above that is really little more than marsh most of the time. This is where USGS research shows the top of the Big Chino aquifer flows out of the ground at the head of the Verde River, entering Stillman at two cubic feet per second. And this flow, the data indicate, will cease at some point in the future after Prescott and Prescott Valley begin pumping massive quantities of groundwater from the Big Chino, drying up both Sullivan and Stillman. Unless, of course, political opinion is more accurate than unbiased scientific analysis and pumping six billion gallons of water each year from the Big Chino really won't impact anything at all.

Weedman's comment dashed any hopes that another endangered species in the Verde River might stop that pumpage. Introducing an endangered species into Stillman Lake will be no additional speed bump for the cities' plan because, Weedman said, the Verde River is already designated as critical habitat for the razorback sucker and, just recently, the upper Verde received a designation as critical habitat for the endangered spikedace minnow. That's enough to  require the cities to file Environmental Impact Statements for their proposed pumpage, should USF&WS decide that data indicate it may adversely impact Big Chino flows to the river. 

Stocking via 'natural flush'

Today, about 98 percent of the fish in Stillman Lake are non-natives. Some, like the flathead catfish, were probably illegally introduced; others, like the sunfish, smallmouth bass and carp, may have migrated there, either up the Verde River (seems unlikely) or down from Granite Creek (not much less unlikely). The non-natives are very successful at out-competing and eating the natives. Yet, the lake's relative isolation and infrequent connection to the Verde River make it an ideal spot for a novel method of reintroducing natives to the Verde via Stillman through natural flood events.

The Stillman Lake project is really an experiment, though one that biologists believe has a high likelihood of success, if you leave out the part about the USGS study showing the cities' proposed pumpage eventually drying up the lake. The idea is to use Stillman as a safe haven for the native species to grow; natural flood events every few years will “flush” them out of the lake and into the Verde River, simultaneously triggering spawning behavior.

Native species like Verde trout and razorback suckers evolved to take advantage of such flooding events which, incidentally, non-native fish don't handle so well. The flooding of 2004-2005 pretty well proves the concept at Stillman Lake and the upper Verde. For years before that flood, electroshock surveys turned up no Verde trout or razorback suckers in the river immediately below Stillman Lake, though biologists counted bucketsful of non-native smallmouth bass and an alarming infestation of “river roaches”- crayfish. The spring after that flood uncounted numbers of fry appeared in the upper Verde below Stillman Lake, and this year that section of river is home to swarms of 6- to 10-inch Verde trout. The flushing-and-spawning phenomenon is apparently at work here.

 
Click photo to enlarge (you may need to hold the ctrl key if you have a pop-up blocker).

One way or another

Biologists propose two alternatives to renovating Stillman Lake. One is to bulldoze away the natural earthen berm that makes Stillman a lake and let most of it drain into the Verde, then go in with nets and electroshockers to remove the fish. Non-native sportfish (catfish, bass) would go to other appropriate locations for angling; natives would go back into the renovated lake. The second, preferred alternative is to net and electroshock the natives and hold them while poisoning the lake; the dead non-natives would be scooped up and buried on-site. Unfortunately, neither method is effective in eradicating non-native bullfrogs and crayfish.

The first alternative, which they call “mechanical,” has some major disadvantages. First is the cost; at one-half to three-quarters of a million dollars, it's about 10 to 15 times more expensive than simply poisoning the lake. Second, the berm is a natural formation created by sediment discharge from Granite Creek entering the river; it works beautifully, so why mess with something that ain't broke and you might not be able to replicate? Third, in addition to breaching the berm, engineers would have to bring in pumps capable of gulping 52,000 gallons per hour in order to stay ahead of the flow of water continually entering Stillman from the Big Chino. Fourth, they have to make sure all that water from breaching and pumping doesn't damage the river channel. Fifth, they'd have to go back at least twice a year to mechanically (electroshock and net) remove non-natives because this method isn't anywhere near as effective as poisoning

“Poisoning,” by the way, is not a term that officials like to use; they prefer “piscicide” and “toxicant” and the more vague “renovate.”

So, renovating Stillman Lake with a piscicidal toxicant looks like the way to go. Biologists would use either antimycin or rotenone; both toxicants derive from natural sources (a fungus or a root, respectively), bind to organics and break down into harmless chemicals within hours. Water flows out of Stillman by, essentially, soaking through the bottom of the berm, which is covered in organic materials, so that the toxicant would break down long before leaving the lake. Even so, biologists would put sodium or potassium permanganate into the Verde just below the berm; this chemical causes the toxicant to break down in a matter of minutes, rather than hours, and is itself harmless to aquatic life. This renovation method would cost between $25,000-$50,000 and would require perhaps two re-treatments in 10 years to keep non-native numbers down.

That's assuming no one deliberately and illegally re-introduces non-natives to the renovated lake. AZG&F would augment the renovation with educational programs explaining the need to keep Stillman strictly native.

Right now Stillman is open to the public but access is through private property or a long walk across State Trust Land or a three-mile hike from the Upper Verde River Wildlife Area downstream, so it doesn't get  a lot of angler action. AZG&F would most likely leave that situation just like it is, neither encouraging or discouraging fishing at Stillman. 

USF&WS wants your opinion on this. You can read the draft environmental assessment of the proposed project on-line at http://www.fws.gov/southwest/es/arizona/, and then submit your comments by April 25. Send them to: U.S. Fish and Wildlife Service, Attn: Stillman Lake, 323 North Leroux, Suite 101, Flagstaff, Arizona 86001. You can also fax them to (928) 266-1099 or e-mail to This email address is being protected from spam bots, you need Javascript enabled to view it