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Last modified
7/14/2009 5:02:35 PM
Creation date
5/22/2009 12:30:34 PM
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UCREFRP
UCREFRP Catalog Number
9368
Author
Gustaveson, W. A.
Title
Cyclical Population Dynamics of Self-sustaining Striped Bass in Lake Powell, Utah-Arizona, 1974-1998.
USFW Year
1999.
USFW - Doc Type
Salt Lake City.
Copyright Material
NO
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<br />day and then again in the evening just before dark. After dark, <br />shad schools disperse and boils are not likely. Striped bass are <br />effective nocturnal feeders and feed on shad subsurface at night. <br />In times when forage is abundant, boils may be rare or <br />half-hearted because shad are easily obtained and schooling <br />efforts are not required to obtain food. Perhaps surface feeding <br />action is at its peak when shad are common but not abundant. <br />Striped bass must now work hard to corner shad for effective <br />feeding opportunities. As shad become scarce, surface feeding <br />opportunities decrease. At the other extreme, malnourished <br />striped bass cannot compete with healthier more aggressive fish <br />and drop out of the school. Forced to forage on their own <br />individual striped bass are inefficient and are forced to expend <br />even more energy. The end result is a decline in physical <br />condition. School fish may be fat and healthy while solitary <br />fish decline in condition. It is possible to catch striped bass <br />in the same area and find remarkable differences in condition <br />between fat school feeding fish and thin individuals. <br />Total elimination of shad from the pelagic zone results in <br />adult striped bass leaving the warm surface layers where shad <br />once resided to seek cooler water at or below the thermocline <br />where less metabolic demand is placed on fish stressed from lack <br />of food. In Lake Powell there is an almost total absence of <br />forage below the thermocline since most small fish and plankters <br />live in the epilimnion. Once striped bass seek cool depths to <br />preserve energy they are doomed to starvation. <br />Zooplankton is abundant enough to provide feeding <br />opportunities for juvenile striped bass regardless of shad <br />abundance. Wind, wave action and associated currents concentrate <br />large schools of cladocerans providing a riCh, but scattered, <br />plankton forage prey base. All fish including striped bass <br />search out and utilize these zooplankton concentrations. An <br />individual stomach sample from a 275 mm yearling striped bass may <br />contain thousands of plankters that weigh as much as 50 g. In <br />years when shad are available plankton is ignored in favor of a <br /> <br />18 <br />
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