An official count of the endangered Moapa dace took place earlier this month showing that the number of dace is rising steadily. Photo by Vernon Robison.

By Vernon Robison

Moapa Valley Progress

The number of tiny Moapa dace swimming in the headwaters of the upper Muddy River continues to increase moderately, according to a survey of the dace taken earlier this month. The August dace count turned up a total of around 713 dace in the system. That is up from last year’s 697 and 508 in 2009.

The survey, conducted by experts from the U.S. Fish and Wildlife Service (USFW) and the Southern Nevada Water Authority (SNWA), takes place twice a year in February and August. It covers 16 reaches of the Warm Springs system.

At each count, a group of about a dozen fish biologists and their assistants gather at the lower end of the system. They then systematically snorkel through the shallow streams on hands and knees, or on their bellies where necessary, in an attempt to count every dace in the system. Careful records are kept on how many fish are seen and their location in the stream.

The Moapa Valley Wildlife Refuge was established in 1979 to protect the Moapa dace which lives only in the headwaters of the Muddy River at Warm Springs. Photo by Vernon Robison.

The highest concentration of dace are still being observed within the boundaries of the Moapa Valley Wildlife Refuge. The Refuge was established in 1979 to protect the dace which was federally listed as an endangered species in 1967.

In the upper reaches of the Plummer Springs, the area of the Refuge’s dace observation window, experts counted 206 dace, down from 393 last August. Still the Plummer Springs source had 108 fish, up from 90 last August. The Apcar Springs stretch, also inside the Refuge, had 67 dace up from 20 last year.

The dace was found to be significantly on the rise within the SNWA property just below the Refuge. In the Plummer Stream reaches, at total of 140 dace were found; up from 69 last year.

Also watched very closely has been the count in the lower Pederson outflow on SNWA property. This outflow was newly created by SNWA crews in 2008 in an effort to restore the stream to its original channel. This month’s count showed 88 dace in that stretch; up from 84 last year and up from only 51 in 2009.

USFW officials say that these continued strong numbers indicate that, despite the major wildfire in the Warm Springs area last summer, the dace population is holding its ground.

Fortunately, last year’s fire took place down-wind from the Refuge where the largest population of dace exist. Experts think that the Refuge provided a safe place for the fish to flee in order to avoid the affects of the fire.

The dace were not so lucky in 1994 when a previous fire engulfed a stand of palm trees in and around the Refuge itself. The population was nearly exterminated then when ash and smoldering palm fronds fell into the water, raising water temperatures and affecting oxygen levels. Only 30 of approximately 1,000 dace in a 250 yard stretch of the Refuge area springs survived.

A more mysterious drop in the dace count occurred suddenly in 2008 when the dace count plummetted from 1,172 in February 2007 to only 459 in the same month of 2008. Officials say they can’t fully account for the dramatic drop. But many locals believe that it was due to over-agressive USFW habitat restoration efforts at the Refuge which were going on during that time.

This month’s good news of rising dace counts was, however, laced with some bad news as well. During the count, scientists identified non-native tilapia living in the South Fork area just below Baldwin Springs. Experts had been trying to eradicate the tilapia from the whole system because the invasive species acts as a predator to the dace. In recent months officials had thought that the eradication efforts had been successful.

“Unfortunately, they found 15 fish in that one stretch only,” said SNWA Warm Springs Conservation Area manager Robert Johnson. “Fish were observed at all different life stages which means that they are successfully breeding in the area.”

Officials plan to treat the stretch, which currently contains no dace, with the chemical Roterone. This chemical, which has been successfully used to kill off tilapia in other stretches of the stream, will be applied early next month, Johnson said.

“We just apply the chemical into every input source of the system to try to expose all the tilapia to it,” Johnson said. “Then we place a detox station in the stream below to remove all of the chemical from the water downstream.”