SOUTHERN UTAH – As Dixie recovers from its second “100 Year Flood” in five years, we wondered how fare our wildlife, our flora and our fauna? Our first story on the subject reports on the fish population in our Virgin and Santa Clara Rivers.
Floods benefit our native fish population, both in their increase and in decreasing the non-native fish invaders. Although the direct results of our most recent river floods (December 21, 2010) cannot yet be quantified until spring this year or later, Native Aquatic Biologist Melinda Bennion, of Utah’s Division of Wildlife Resources, Washington County Field Office, tells us what is known based on the 2005 Flood.
“More water is always good for the fish; lower temperatures in the summer are always good for the fish. Using 2005 as a reference, our native fish population had an increase as a result of the 2005 flooding,” Bennion said.
The flood and its aftermath conditions “increased flows for the whole year in 2005 which decreased summer temperatures in the river, and increased base loads” throughout the region.
The Virgin River itself is habitat to six native species of fish, two of which (Woundfin / Plagopterus argentissimus, and Virgin River Chub / Gila seminuda) are endangered.
“We saw increased populations for all six native species,” Bennion said, continuing her assessment of the 2005 flood’s impact.
Nonnative species do inhabit Southern Utah’s rivers as well, introduced by people accidentally or intentionally through purposes such as bait for fishing.
Floods help address the problems of nonnative species, Bennion said; “really,” she said, “flooding of the rivers is good for removing non-native species. They can’t handle turbidity that comes with the flooding. It accumulates sand. When the Virgin River occupies its flood plain, it starts increasing the sediment load because it runs through sandstone and sand. Our fish are adapted to be able to survive in turbid environments whereas nonnative species have trouble getting enough oxygen when it is that turbid. Their gills get silted so they have trouble breathing.”
The primary concern in any flood situation is that nonnative fish are able to move upstream during the flooding because the barriers and diversions Wildlife Services has imposed aren’t as effective when there’s a flood – the nonnative fish can bypass them.
One of those nonnative fish that Bennion indicates the Division of Wildlife Resources is trying to eradicate throughout Utah is the red shiner (Cyprinella lutrensis). The red shiner will “out-compete native fish for shelter, food resources and could easily replace native fish if we didn’t do anything,” she said.
“There is red shiner in Arizona, so our concern is that during these flooding events the water levels are high enough that they can come upstream . . . we don’t want them to re-colonize because we’ve spent years trying to get rid of them.”
Efforts to eradicate Southern Utah’s rivers of the red shiner include mechanical means (nets for extraction) and, when appropriate, chemical removal.
Asked if there is a chemical that will target one fish only, Bennion said there is not.
“Unfortunately no, but we identify a section that we want to reach. (Then) we go through a few weeks of extracting the native fish and moving them upstream, and then we can treat the identified section, and add a detox station just below it. It will definitely kill anything aquatic (anything that has gills).”
She continued, impressing that “part of native fish recovery is nonnative fish removal.”
As floods impact rivers, Bennion summed up the floods’ impacts on rivers, and thus on fish populations, this way: “Historically the system is very cyclical, flashy, you want variation in the hydraulity – the more diverse, the more positive the response. So long periods of drought have negative impacts.”
Ergo, when it comes to Southern Utah’s floods, its fishes fare swimmingly.
Ed. note: Featured image of DWR aquatic biologists substituted into the story at a later date.
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