DWR to poison the Virgin and lower Santa Clara Rivers to eradicate non-native fish

DWR Aquatic Biologists, Native Woundfin project March, 2011 | Photo courtesy of DWR

WASHINGTON COUNTY – The Utah Division of Wildlife Resources, in coordination with the Washington County Water Conservancy District and the U.S. Fish and Wildlife Service, is conducting a treatment project to benefit and protect native fish species in the Virgin and Santa Clara rivers.

With the winter flooding 2010 / 2011, certain barriers that the DWR had previously installed to prevent the non-native fish from invading the rivers upstream were washed out. One example is the concrete barrier that DWR had installed below the I-15 river overpass just North of Bloomington Walmart. As a result, the non-native fish have made their way upstream and are overtaking habitat needed for the native fish.

Red Shiner and Fathead Minnow have therefore expanded in the Virgin River drainage. Red Shiner moved upstream during last winter’s flooding and Fathead Minnow invaded the lower Santa Clara River from nearby ponds.

In areas where these fish have become abundant, native fish populations have declined. Past treatments have been successful in preventing invasive fish species from spreading upstream. The present project is intended to remove Red Shiner and Fathead Minnow and thereby increase available habitat for native fish.

The Santa Clara River was treated as originally scheduled Oct. 3-8, 2011, said Melinda Bennion, Native Aquatic Biologist with the DWR. But treatment of the Virgin River was delayed due to too high water flow in the Virgin earlier this month. She said that treatment of the Virgin is contemplated sometime this week (probably Wednesday, depending upon pending assessment of current flow and other conditions).

Red Shiner | Courtesy of Utah Division of Wildlife Resources

The project includes using rotenone to chemically treat the Virgin River and the lower Santa Clara River in order to remove two invasive fish species (Red Shiner and Fathead Minnow).

The Virgin River treatment section starts at the Johnson Diversion in St. George and ends downstream at the State Line Barrier near the Arizona border. The Santa Clara River treatment section begins near the town of Santa Clara and ends at the confluence of the Virgin River.

Prior to the rotenone treatment, native fish were salvaged from the treatment sections. Salvaged fish were moved to adjacent sections of the river that will not be treated.

Rotenone, the chemical used to treat the river, is a natural product derived from the roots of South American plants. Rotenone completely decomposes without leaving any harmful residues and is specifically toxic to fish. “It kills everything,” said  DWR Biologist Brooke Cox.

“Everything” actually means everything with gills, explained Bennion.  Rotenone poses no threat to other wildlife, birds, livestock, or humans at the applied concentrations. DWR has used rotenone as a fish toxicant on many projects and has not encountered any problems with its use concerning human safety, recreation, irrigation or livestock.

“It is only harmful to fish,” said Bennion. “The concentrations we use  are 3 parts per million, safe for cattle, people, and other animals; concentrations are high enough to kill the fish, it interacts with the way we take in oxygen, if you [or animals] don’t have gills it will not affect you.” She added, with obvious humor, that it would not be a good idea for anyone to drink straight rotenone.

In order to avoid any downstream impacts (outside of the target area) rotenone will be detoxified. Potassium Permanganate (KMnO4), a commonly used water purifier, will be added to the stream to remove the rotenone. Although Potassium Permanganate will turn a short portion of the river purple, it is harmless and breaks down in a very short time.

This project is part of the Virgin River Program, which is a collaborative effort among local, state, federal and private partners to balance human interests and conservation of the unique Virgin River system.

Of note, the woundfin is one of the native fish threatened, which DWR biologists have been working diligently to preserve.  Woundfin are now only found in the Virgin River, ranging from Pah Tempe to Lake Mead, due to a declining population. See St. George News story on the Woundfin and one of these efforts, many  years in the making, published earlier this year.

For further information, contact Lynn Chamberlain, Utah Division of Wildlife Resources, Cedar City, Utah at (435) 865-6100.

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