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Last modified
7/14/2009 5:02:33 PM
Creation date
5/24/2009 7:27:30 AM
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UCREFRP
UCREFRP Catalog Number
8133
Author
Collins, K. and D. K. Shiozawa.
Title
The Effects of Fish Predation on Backwater Invertebrate Communities of the Green River, Utah\
USFW Year
1996.
Copyright Material
NO
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DISCUSSION <br />The results of our experiment support the conclusions of several studies of fish <br />predation on invertebrates in pools and soft substrates (Wilzbach et at. 1986, Schlosser and <br />Ebel 1989, Angermeier 1985, Gilliam et at. 1989). This is in contrast to studies of coarse or <br />rocky bottomed streams which showed no significant density effect of fish predation (Allan <br />1982, Reice 1983, Flecker and Allan 1984, Culp 1986, Reice and Edwards 1986). There are <br />many possible reasons for this, several of which are discussed by Allen (1983). One is that in <br />the soft sediments of slow moving streams or pools, where there is little current and the <br />organisms exhibit very little propensity for drifting, fish must actively forage for their prey. <br />In contrast, coarse bottomed streams usually have a swifter current due to higher gradient, and <br />are often dominated by fish species which wait in pools for their prey to drift by. In addition, <br />the rapid prey exchange caused by the steady immigration of persistently drifting insects in <br />rocky streams may overwhelm the local impacts of predators (Sih and Wooster 1994). <br />Another possibility for the difference in predation among substrate types may be the ability of <br />prey to find a suitable refuge. It is possible that rocky substrates offer more refuges than do <br />soft substrates (Allan 1983, Gilliam et at. 1989). <br />Despite the similarity of the results of our study with studies of soft bottomed streams, <br />the backwater habitats that we sampled are not usually associated with smaller streams. Except <br />for their lack of vegetation they were very similar to the littoral region of a lake or pond. <br />Backwaters have higher standing crops of invertebrates than the main river channel (Mabey <br />1993, Wolz and Shiozawa 1995). This higher food resource density is probably an important <br />factor in attracting fish to the backwaters.
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