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Last modified
7/14/2009 5:02:36 PM
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5/24/2009 7:27:25 AM
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UCREFRP
UCREFRP Catalog Number
9544
Author
Collins, K., P. and D. K. Shiozawa.
Title
The Effects of Fish Predation on Backwater Invertebrate Communities of the Green River, Utah.
USFW Year
1994.
USFW - Doc Type
Provo, UT.
Copyright Material
NO
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areas is a result of increased survivorship or immigration is unclear. On the other <br />hand, while the zooplankton could also fit through the mesh, research indicates that <br />they avoid unnatural structures such as walls (Zaret 1980). This leads us to believe <br />that higher densities of adult copepoda and E. speratus are a result of increased <br />survivorship. <br />The fact that adult copepods and E. era s were significant in the plankton, <br />but not in the benthos, suggests that they are more susceptible to fish predation while <br />in the water column than while in the benthos. This is supported by the observation <br />that the smaller copepod life stages (nauplii and copepodites) were the most <br />numerous planktonic groups, yet showed no density effects of fish predation, <br />suggesting the possibility of size-selective predation (Brook and Dodson 1965). Since <br />the water was quite turbid (secchi depth averaged 22 cm on a calm day) the "reactive <br />distance" of a visual predator (such as fish) would have to be quite close for <br />something as small as a nauplius or copepodite (O'Brien 1979). <br />Indirect effects <br />The benthic densities of the naupliar and copepodite stages of copepods show <br />a negative effect of diminished fish numbers, which is probably due to increased level <br />of corixidae and Tanypus. The fact that they show significance in the benthos but not <br />in the plankton supports this since Tanypus feed in the benthos and the corixid genus <br />Tricorixa is known to feed on benthic organisms (e.g. chironomidae and oligochaeta, <br />see Merritt and Cummins 1984). While there was a direct effect of fish predation on <br />the density of E. s er u (an herbivore) chlorophyll a levels indicate there is no <br />12
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