WSP06185 - Laserfiche WebLink

Home Browse Search

I i p. ~ us with an estimate of the change in overall habitat for this reach and then discuss the relative importance to the aquatic food base for the entire river. ~ ~ t ~ ~ .~ " ,~ " il l ~~. ..1 ";' I 1. l .' ~ Pg. 205, C. 1, P. 1. We are not aware of any data to support the speculation regarding limited access at different flows, other than incidental observations by Valdez at Nankoweap Creek. What studies were conducted on which tributaries to support this conclusion? This seems to create a problem where none has been documented. What conditions exist, other than waterfalls, to limit access? ,If flows fluctuated and fish were denied access at one flow, what would prevent their gaining access a few hours later when flows changed? Pg. 205, C. 1, P. 3. Your statement that native fish reauire the refuges is misleading. We agree if young native fish are washed into the mainstem, thermal refugia may be needed to survive; however, tributary recruitment may be adequate to sustain healthy populations without mainstem thermal refugia (e.g., humpback chub in the LCR). We agree with your statements regarding mortality causes including temperature shock and exposure to non-native predators as studies support this but we have seen no documentation to support your hypothesis on energy expenditures causing direct mortality in native fishes and believe the DEIS should be modified to delete the phrase. Also, we agree with your statement that effects on adults, if any, is limited to indirect effects through association with the aquatic food base. '.. ;". .~ This paragraph describes expenditure of energy for chub under normal flows as probably higher than under steady flows but it is incomplete. Cladophora drift and other food sources also is higher under normal flows than under steady flows. According to Valdez' talk in Moab, Utah (winter, 1993), the condition of chub under normal operations was apparently better/higher than under steady flows, possibly as a result of both their typically sedentary activity levels and the increased food supply. Pg. 205, C. 1, P. 4. The number and kind of backwaters is dependent on preceding conditions as much as the present flow condi tions. Your statement regarding maintenance of backwaters with high flows should be expanded. Also, although some backwaters are lost during flooding due to shifting of sand bars, they are replaced by others after floods subside. .~.. . "'.4 -..:: >i ~<! . K :} '~ '"" C" .l:~ ..3~ :~ ii ~;Z Tributaries may adequately sustain healthy populations. In instances, mainstem backwater habitats may not be required. discussion of these possibilities seems in order. these Some Pg. 205, C. 2, P. 1. Removal of non-natives is impossible but perhaps cold water could be used to control their numbers. This is why habitat improvements to foster better warmwater conditions may 32