9547 - Laserfiche WebLink

Home Browse Search

zooplankton and benthic organisms, and postlarvae as small as 30 mm have been observed consuming other fish (Muth and Snyder 1995). Late summer and autumn is a critical period for growth and survival of young Colorado ~ pikeminnow. The abundance and growth of young pikeminnow in the Green River are favored by relatively low flows, and impaired by high flows that inundate and damage backwater habitat: catch and growth rates during late summer and autumn were higher in the low flow years (1979-1980) and lowest in years with unusually high releases (1983-1984) from Flaming Gorge Dam (Tyus et al. 1987). This relationship suggests ~ that the flows that optimize growth and survival of small pikeminnow vary with time of year and that postlarval survival depends on the availability of backwater nursery habitat (Tyus and Haines 1991). Most larvae produced by one population will use one nursery area downstream (Figure ~ 3). Larvae produce in the Grand Valley region of the UCR drift downstream to a nurcery area in the vicinity of Moab, UT (Valdez et al. 1982). In the Green River, there are two nursery areas; one is 130-150 km downstream from the Yampa River spawning reach, and the other is 130-150 km downstream of the Green River spawning reach (Tyus et al 1982b and 1987, Tyus and Haines 1991). The nursery habitat is created ~ with the gradually decreasing flows that follow spring runoff and persists through the summer and early autumn. Increased releases from reservoirs in autumn and winter may inundate this habitat. The quantity and quality of these habitats are thought to be crucial to successful recruitment. . Aerial photography and videography have been used to assess the relationship between nursery habitat condoions and flow in the river. In the Green River, aerial studies coupled with ground interpretation have shown that maximum area of backwaters occurs at flows in the range of 30 to 50 m3/s (Pucherelli and Clark 1989). Flows above or below this level reduce the number of backwaters available as nursery habitat. However, it is clear that a simple flow vs. backwater area relationship does not ~ exist. Instead, the area and number of backwaters depends on a complex relationship that is sensitive to the timing, duration, and magnitude of flow and sediment inputs, as well as the physical characteristics of the riverine habitat. Other studies of the relationship between backwater habitat and flow are being conducted by the Bureau of Reclamation and the Utah Division of Wildlife Resources for the UCR (Fenton 1996), ~ but results are not yet available. Nutrient dynamics in the backwater nursery habitats have not been studied thoroughly, but some studies have been done in the Green River. Backwaters in the Ouray area, where larval pikeminnow were abundant, were richer in food than similar habitat ~ upstream. Reduced fluctuations in water level near Ouray may have resulted in more stable backwater habitats and possibly reduced exported nutrients and food (Grabowski and Hiebert 1989). 16