There's a new kid in town at Rose Creek Reservoir at Hawthorne Army Depot, in Hawthorne, Nev. A fish called the Lahontan tui chub has taken up residence.
Back in 2006, a group of biologists developed a cooperative, extensive monitoring effort of the ecosystem of Nevada's Walker Lake. The lake's ecosystem was threatened due to decreasing water volume.
At about the same time, Karie Wright, Fisheries Biologist with the Nevada Department of Wildlife, began testing endangered tui chub populations to determine any genetic uniqueness. "Out of several tui chub populations tested, the Walker Lake Lahontan tui chub had the greatest genetic diversity, or in layman's terms, it was very healthy, and was the best candidate for preservation," said Wright. By 2008, Wright had targeted the tui chub of Walker Lake for the purpose of establishing a refuge population for this native fish.
But upstream water diversions continued to decrease Walker Lake's volume. When lake volume decreases, total dissolved solids' concentration increases. TDS is directly related to the purity of water and affects everything that consumes, lives in or uses water. The TDS issue at Walker Lake resulted in an increase in saline, or salt levels, which was leading to increasingly toxic living conditions for the tui chub. The exact level of toxicity at Walker Lake that would kill the tui chub population was not known. So the bottom line was to find a refuge very soon.
The search for a refuge began in 2008. Wright was exhausting all of her prospects when her boss asked about Rose Creek Reservoir at Hawthorne Army Depot. Wright contacted John Peterson, Natural Resources, at Hawthorne. "Immediately, John was interested in what we were doing and in helping our cause," Wright stated. "He truly has an interest in helping fish and wildlife in the state."
Less than three miles west of Walker Lake, Rose Creek Reservoir covered three to four acres, stored approximately 50 acres per foot of water, and was about 40 feet deep in the center. The water clarity was high, there was little underwater vegetation, no vegetation on its banks, and minimal sedimentation. No other fish species lived in Rose Creek Reservoir, and testing showed an abundance of food available for the tui chub including various phytoplankton and zooplankton (microscopic plants and animals). The only potential predators would be fish-eating birds and bears. In light of the plethora of positive factors, Rose Creek Reservoir was chosen as the refuge for the Lahontan tui chub.
In October 2009, 176 tui chub from Walker Lake were successfully transplanted into Rose Creek Reservoir. For identification purposes, all of these fish were given a right ventral fin clip. The initial mortality rate of the chub acclimating to the fresh water appeared to be about ten to fifteen percent.
But by the summer of 2010, no adult chub or offspring was observed. Wright said, "They were not observed. That doesn't mean they are not there. I marked them, so follow-up netting should confirm this. Or they could have died. They were moved after spawning and a hot summer in the bad conditions at the lake. They were mostly in poor condition and may not have survived the acclimation to the fresh water."
On 23 June 2010, 88 actively-spawning tui chub were netted from Walker Lake, and given a left ventral clip. The object was to plant pregnant chub so that even if they could not survive the fresh water acclimation, they might spawn before dying and the offspring would survive in the fresh water.
They were placed in a tank of a 50/50 mixture of fresh/lake water and held overnight for acclimation to fresh water, like that of Rose Creek Reservoir. But ammonia that had accumulated on the bottom of the fish tank was dispersed into the water column during aeration and created a fatal mixture that killed all of the fish.
A week later, on 1 July 2010, 170 tui chub were netted at Walker Lake, given a left ventral clip, and because of time constraints, were directly transplanted to Rose Creek Reservoir without acclimation.
On July 20 a trap net was set for surviving adults, and on July 22, eight adults with a left ventral fin clip were captured in the net. All appeared to be in good health and were given a partial clip to their anal fin to identify them. A multitude of young tui chub were observed along the shoreline of Rose Creek Reservoir. The new kids had most definitely arrived!
What is expected to happen to the Lahontan tui chub at Rose Creek Reservoir between now and the spring of 2011' "Hopefully, they have a happy winter in the refuge," said Wright. "It does not freeze, so they should be OK. In the spring, I will augment the population with more Walker Lake chub, if they are still there."
Also in the spring, Wright will use a tank of Walker Lake water to conduct an experiment on re-acclimating adult chub. "Even though the fish went to the fresh water OK, they may not go back to the salty water OK. But the experiment may show a TDS level that we should shoot for when reintroducing the chub," said Wright.
It is necessary to continue augmentation of the chub at Rose Creek Reservoir with adult Walker Lake chub so that the genetic ability to acclimate to salty water is not lost. If Walker Lake has a great flood season, it could gain 20 feet, and the salinity would greatly decrease. Then some of the refuge chub could possibly be reintroduced to Walker Lake.
Even if the saline levels of Walker Lake decrease after a positive flood season, "...without a consistent water source for the lake, it is still important to have this population of tui chub secured at Rose Creek Reservoir," said Wright. "We are very optimistic, after fostering such great working relationships with Hawthorne Army Depot, that the tui chub refuge will be a great source for a dying lake population of fish."
It's obvious the "new kids" will play a vital role in propagating a refuge population of the native Lahontan tui chub in Rose Creek Reservoir at Hawthorne Army Depot.
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