Study Plan - Biological Resource Responses to Fall Steady Experimental Flows Feruary 2010

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Otolith (inner ear bone) data highlights the importance of using process -level measurements to document biological responses to the FSEF. Korman and Campana (2009) found that steady flow releases conducted 1 day /week (Sunday) in January through March of 2003 through 2005 led to measurable increases in growth (presumed to correlate with measured otolith responses) of young -of- year rainbow trout (Oncorhynchus mykiss) below Glen Canyon Dam. Because this was documented in the Glen Canyon Dam tailwaters reach (RM 0 to -15) in winter when nearshore temperatures were likely no different from the mainstem, this study indicates that stability of nearshore habitats without concomitant warming can benefit rainbow trout. It is possible that steady flows in September and October, a time when nearshore warming is likely modest, will also benefit juvenile humpback chub simply by stabilizing nearshore environments. However, results obtained from trout may not be directly comparable to other fishes, including humpback chub. Food Resources Constant discharge will increase available food resources if algae and invertebrate growth rates are higher when discharge is constant or if accumulation of algae and invertebrate biomass is higher during steady flows relative to fluctuating flows (Production is total biomass accumulation per unit time, P= Growth Rate *Biomass). The two most likely mechanisms whereby stable discharge could increase algae and invertebrate growth rates are through (1) warming nearshore habitats and /or (2) delivering nutrients to algae and food particles to invertebrates should constant water velocities support higher growth rates relative to water velocities that fluctuate on a daily basis. Experiments at the Artificial Stream and Pond Research Facility at the Loyola University Chicago directly evaluated these two mechanisms and found strong support for mechanism 1 (temperature), but results were actually contrary to mechanism 2 (stable water velocity) (Kennedy and others, U.S. Geological Survey, written commun., 2009). Net primary production of Colorado River algae and individual growth rates of larval black flies were more than twice as high in 15 °C streams relative to 10 °C streams, indicating minor increases in the amount of nearshore warming (that is, 5 °C) can lead to substantial increases in algae and invertebrate growth rates (see figs. la and 2a). In contrast, net primary production was about 50 percent lower in streams with constant daily velocity (15 cm /second) relative to streams with either low (velocities of 22 to 44 cm/second within a day) or high daily velocity fluctuations (11 to 67 cm/second within a day; see figs. lb and 2b). Individual growth rates of larval black flies were lowest in the stable flow streams on the two occasions these measurements were made, but the differences were not statistically significant. There were no significant interactions between water velocity and temperature for any of the response variables evaluated. Growth and production in stable flow streams was likely lower than fluctuating streams because the rate of nutrient and food delivery was lower in stable streams. That is, the water velocity of the stable treatment streams was lower than the average water velocity of fluctuating treatment streams. This aspect of the experimental design is similar to the FSEF, with stable discharge (velocity) in September and October being lower than discharge (velocity) in July and August. It should be noted that the water velocities evaluated are lower than reach - average velocities in the Colorado River. Regardless, these results indicate water temperature has a strong and positive effect on algae and invertebrate growth rates while stable water velocities do not (Kennedy and others, U.S. Geological Survey, written commun., 2009).