WSP11633 - Laserfiche WebLink

Home Browse Search

6 CLARKSON EI' AL. also occur in upper reaches during this period. Both tributary-spawned fish entering the mainstem and mainstem-spawned fish would experience temperature conditions better suited to faster growth. Such a temperature regime likely wouId also benefit the Lee's Ferry tailwater fishery by providing more optimal temperatures for trout growth (LechIeitner 1992): .. , Installation and operation of a MUS to warm the CoIorado River in Grand Canyon and introduce seasonality of water temperatures may affect several aquatic and riparian ecosystem components. Potential effects incIude: (I) alteration of algal species composition and productivity; (2) alteration of invertebrate species composition and productivity; (3) invasion and enhancement of additional non-native fishes from L3ke Mead, L3ke Powell, or internal tributaries, and; (4) increases in the incidence of fish diseases and parasites. We emphasize, however, that proposed maximum release temperatures are only S-60C higher than present, and that hypolimniaI releases will continue to be delivered during autumn and winter months. Greatest concern expressed to date for unintended effects of increasing water temperatures is. for the possible invasion and establishment of additional non-native fishes or entrenchment ofexisting species, which could potentially offset the benefits of a MUS. We believe that a lack of important environmental requirements, other than water temperatures, serves to reStrict the distribution and abundance of non-native fishes in Grand Canyon (Valdez 1992). 111ese conditions should continue to exert negative effects on invasion and expansion of the . ill).natives, Furthennore, as discussed above, the recurring impacts of periodic flood events ~ouid serve as a major control agent in the system. . - - Incieasing and seasonally adjusting water temperatures in Grand Canyon would remove a knoWn impediment to successful teprodliCtionby native fiShes in themainstream.and improve surviVal and the potential for rapid growth by young fishes. If these impediments from cold water temperature are relieved, we believe the optimal scenario for mainstem hydrology will be altered, and there can be more flexibility in the delivery of water. For example, a major reason for maintaining high flows during reproductive and earIy growth periods under emting conditions is to retain most young fishes in tributaries. If mainstem reproduction is successfidand young-of-the-year fishes experience faster growth and greater survivorship Iii Warmer Colorado River waters, the importance of mainstem habitats, both reproductive anel reanng, will increase relative to tributary habitats; . Thus, mainstem hydrology should bC~odified accordingly to increase the advantage to young fishes occupying these habitats. ;;'.)1\:',; . . . '-, . . . . . ", . . ~~ 'on the timing of native fish reproduction in the Upper CoIorado and Green ri~ers ~.. - ", . . ~ve to hydrology and water temperature, 'we believe that mainStem reproduction in Grand "canyon (excepting razorback. sucker) will ~gin on the descending limb of the hydrograph ~'. ".. . . once water temperatures exceed IS C. Given the suspected limits to warming with a MUS, \.