GENERAL31841

• Permit No: M1999002
• IBM Index Class Name: General Documents
• Doc Date: 7/22/1999
• Doc Name: FINAL ENVIRONMENTAL IMPACT STATEMENT VOLUME 2 APPENDIX L
• Media Type: D
• Archive: No

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primarily backwaters, eddies, and pools. During low flows, the fish
used slow and fast runs almost exclusively. The change in habitat use
without a corresponding change in relative habitat availability
indicates that other factors also influence habitat selection. These
factors could include changes in quality of physical habitat features
such as diversity, depth, dissolved oxygen, etc., or changes in biotic
interactions. Osmundson et al. (1995) interpreted the behavioral
changes as reflective of suboptimal conditions; the behavioral changes
demonstrate the ability of the species to modify their habitat use
patterns to temporarily cope with adverse conditions and do not
demonstrate habitat preferences under optimum conditions. Osmundson
et al. (1995), therefore, based their flow recommendations on the
habitat-selection behavior of adult observed during the higher
somewhat more natural flow conditions.
Winter (November-March): Osmundson et al. (1995) reported that flows
during the winter are usually moderate because no water is diverted
for irrigation and because additional water is released through
upstream dams to increase reservoir storage capacity in anticipation
of spring runoff. The relative availability of slow runs and riffles
during the winter was very similar to their availability during
summer. As in the summer, backwaters, eddies, and pools were the
preferred types of habitat in the winter. However, whereas eddies
were most preferred in summer, pools were most preferred in winter.
Adult 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 area of pools increases as
flows decrease and slow runs lose velocity. Because Osmundson et al.
(1995) did not sample low flows in the winter, they could not
determine if pools would still be preferred in the winter at lower
flows. Therefore, they recommended winter flows at the moderate flow
level which maximized weighted area of preferred habitats.
Spring (April-July): Osmundson and Kaeding (1989) reported that use
of low velocity habitats such as backwaters and flooded gravel pits is
greatest during the spring runoff. It is believed that 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 are considerably warmer
than the main channel during the runoff, these habitats allow to
extend their growing season substantially. The earlier warming of
these habitats may also be important in enabling to reach spawning
condition by the time flow and temperature in the main channel are
optimum for spawning. Osmundson et al. (1995) reported that the
numbers of backwaters and flooded gravel pits increases with
increasing spring flows. (Although the number of backwaters
eventually decreases as increasing flows convert backwaters to
aidechannels, the number of other low velocity habitats likely