ST. GEORGE — Eight months after being drained and chemically treated to eliminate three fish species that had been illegally introduced into Kolob Reservoir, wildlife officials made a visit this week to look for remaining signs of the unwanted fish.
“We were successful as far as we can tell,” Richard Hepworth, aquatics manager for the Utah Division of Wildlife Resources, said Thursday.
In early September 2018 it was announced by the DWR and Washington County Water Conservancy District that Kolob would be drained and subject to rotenone treatment. This was in response to discovering that three species of fish – yellow perch, green sunfish and bluegill – had been illegally stocked in the reservoir by an unknown party.
Two of the illegal fish posed a particular threat to the trout stocked at the reservoir by DWR, Hepworth said. The fish were also considered a threat to the endangered fish in the Virgin River should they somehow make it into the river system
“Moving fish around can cause a lot of problems and cost a lot of money,” Hepworth said.
According to the DWR, among the problems the transplanted fish can create involve outcompeting native fish for food sources, carrying parasites and pathogens that can harm native fish, preying on native fish, and surviving and reproducing to the point of becoming an invasive species.
The dumping of illegal fish, usually pets like gold fish, into outdoor bodies of water is illegal under state law. It has also led to the DWR’s “Don’t ditch a fish” campaign which usually takes the form of a warning sign posted next to a pond or other body of water.
The reservoir was subsequently drained. Remaining areas were treated with the rotenone, a natural product derived from the roots of South American plants. It’s specifically toxic to gilled organisms because it interrupts oxygen uptake from the water at the cellular level. It also completely decomposes without leaving any harmful residue.
With the above average snowpack that Southern Utah and much of the state experienced over the winter, Kolob Reservoir refilled and soon it came time for wildlife officials to check it for any signs of the illegal fish.
Hepworth and his people went out on the water Monday and Tuesday with nets in order to catch any fish, but ultimately pulled out empty nets. On Wednesday and Thursday, they began restocking the Kolob reservoir with trout.
Anglers shouldn’t get too excited about the news though, at least not yet.
“Fishing will be a little bit tough this first year” after restocking, Hepworth said.
Food for the reintroduced fish will be plentiful so not as many may be drawn to an angler’s bait. This will change in time, however.
“Fishing should be back to normal by next year,” Hepworth said.
In 2015, Gunlock Reservoir had to be drained and rotenone-treated due to illegally-stocked fish.
Wildlife and water officials have also had to deal with illegal smallmouth bass introduced at the Quail Creek Reservoir. While efforts to remove the fish have helped keep the population from expanding, rotenone treatment remains a possibility.
“Visitation to our reservoirs has increased significantly, and we’re happy to see so many guests using and enjoying the reservoirs for a variety of recreational purposes,” said Ron Thompson, water district general manager. “But we have to remember that the primary purpose of a reservoir is to store the water that’s needed for our residents and businesses. Actions that interfere with this primary purpose are disconcerting.”
The DWR, water district and sportsman groups have offered a $3,000 reward for information leading to the conviction of the parties responsible for illegally stocking the fish at Kolob.
If convicted, consequences could include paying the cost to treat the reservoir, which is estimated to run between $15,000 and $20,000, according to the DWR.
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