Why some native fish in the upper Colorado River basin are endangered (Continued)

Other factors

Some portions of the upper Colorado River basin have high levels of selenium. Animals need this naturally occurring element in trace amounts. But in larger concentrations, selenium can cause severe birth defects in wildlife. Researchers are conducting studies to determine if selenium is affecting the ability of endangered fish to survive and produce healthy offspring.

Some native fish have been killed by anglers who did not release the fish properly. Also, some anglers may prefer to catch northern pike, channel catfish and other non-native sport fish they may consider more desirable. After hooking a native fish, they may have tossed it on the riverbank to die.
In the mid-1960s, efforts were made to reduce native fish populations and make way for stocking non-native sport fish in Flaming Gorge and Navajo reservoirs. This was done with the use of rotenone, a substance extracted from the root of the derris plant. (Rotenone reduces fish populations by temporarily preventing fish from absorbing oxygen through their gills.) Following the use of rotenone, biologists found that although the total number of fish had dropped, the ratios of various species remained about the same. This led them to conclude there had been no lasting effect on the native fish species.

Other factors that may have contributed to the fishes' decline include pollution and parasites. Among the chubs, hybridization may also be a factor.
Endangered Colorado River basin fish Historical perspective on these fish Why these fish are endangered Upper Colorado River Recovery Program Improving habitat for the fish
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