2010-11-16_PERMIT FILE - C1996083A ‎(27)‎

• Permit No: C1996083A
• IBM Index Class Name: Permit File
• Doc Date: 11/16/2010
• Doc Name: After 1996
• Section_Exhibit Name: Volume III Exhibit 09 Wildlife
• Media Type: D
• Archive: Yes

• 19
was very similar to their availability during summer. As in the summer, backwaters, eddies, and
pools were the preferred rvpes of habitat in the w:-.-er. However, whereas eddies were most
preferred in summer, poois were most preferred in winter. Adult pikeminno~v used fewer habitat
types overall during winter than during summer. Although fast runs and riffles were used during
the summer, they were not used during the winter. The colder water temperatures in winter
which cause lower metabolic rates may account for the avoidance of high velocity sites.
Absolute azea of pools increases as flows decrease and slow runs lose velocity. Because
Osmundson et al. (1990 did not sample low flows in the winter, they could not determine if
pools would still be preferred in the winter at lower flows.
Spring (April-July): Osmundson and Kaeding (1989) reported that pikeminnow use of low
velocity habitats such as backwaters and flooded gravel pits is greatest during the spring runoff.
It is believed that pikeminnow use these habitats during the runoff to escape the high velocity,
low temperature flows of the main channel. Because backwaters, flooded gravel pits, and other
low velocity habitats aze considerably warmer than the main channel during the runoff, these
habitats allow pikeminnow to extend their growing season substantially. The eazlier warming of
these habitats may also be important in enabling pikeminnow to reach spawning condition by the
time flow and temperature in the main channel aze optimum for spawning. Osmundson et al.
(1995) reported that, in the 15-mile reach, the numbers of bacl.~vvaters and flooded gravel pits
increases with increasing spring flows. (Although the number of backwaters eventually
decreases as increasing flows convert backwaters to sidechannels, the number of other to
velocity habitats likely increases as increasing flows inundate additional bottomlands.)
decrease in the magnitude, duration, and frequency of high spring flows, then, decreases
quantity and the duration and frequency of availability of important low velocity, higher
temperature habitat in the spring. This could be affecting pikeminnow growth and spawm
success.
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Also, the quantity and frequency of availability of inundated floodplain depressions used by
razorback suckers for spawning is dependent on the magnitude and frequency of spring flows
necessary to inundate these azeas. The decrease in the magnitude and frequency of spring flows
necessary to inundate floodplain depressions is believed to be largely responsible for poor
razorback sucker spawning success.
Biological Environment
Food supply, predation, and competition aze important elements of the biological envirotunent.
Food supply is a function of nutrient supply and productivity, which could be limited by the
presence of contaminants. The modification of flow regimes, water temperatures, sediment
levels, and other habitat conditions caused by water depletions has contributed to the
establishment of nonnative fishes. Predation and competition from nonnative fishes have been
• cleazly implicated in the population reductions or elimination of native fishes in the Colorado
River Basin (Dill 1944, Osmundson and Kaeding 1989, Behnke 1980, Joseph et al. 1977,
Lanigan and Berry 1979, Minckley and Deacon 1968, Meffe 1985, Propst and Bestgen 1991,