9484

• UCREFRP Catalog Number: 9484
• Author: Osmundson, D. B., V. L. Ryel, V. L. Lamarra and J. Pitlick
• Title: Flow-Sediment-Biota Relations
• USFW Year: 2002
• USFW - Doc Type: Implications for River Regulation Effects on Native Fish Abundance
• Copyright Material: YES

1732 D. B. OSMUNDSON ET AL. Ecological Applications
Vol. 12, No. 6
160
120
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FtG. 6. Mean total (top) and mean relative (bottom) depth-of-free-space (DFS) in run and riffle substrates of stratum 9
(left) and stratum 8 (right) during base flows of 1996-2001. Total DFS is the absolute distance from the top of surface rocks
to the level of embeddedness; relative DFS scales absolute distance to the median rock width (measured across the b-axis)
at each site.
of adult pikeminnow (F, , = 8.0, P = 0.025, r2 = 0.53),
an expected result because of the strong relationship
between biomass of all fish and riffle area (F,,, = 20.6,
P = 0.001, r2 = 0.70). The stronger relationships of
adult pikeminnow with numbers and biomass of other
fish suggests that food availability is more important
than the physical habitat provided by riffles.
Given that food availability was most important, the
regression for adult pikeminnow densities with biomass
of other fish was extended to include area of runs and
area of nonriffle/run habitats. This was conducted to
assess if the area of other habitats, when combined with
food availability (which strongly correlated with rif-
fles), further explained the variability in adult pike-
minnow densities. This regression was highly signifi-
cant (F3,5 = 84.1, P = 0.0001, r2 = 0.98), with all
independent factors significant (P G 0.02) and no ev-
idence of multicollinearity (condition number = 4.05).
When the regression was conducted in a stepwise man-
ner, biomass of other fish explained 76% of the vari-
ation in density of adult pikeminnow while the other
two factors explained 65% of the residual variation,
suggesting that habitat heterogeneity and total wetted
area (as reflected by the major habitat type, runs) may
also influence adult pikeminnow distribution when
overlain on food resources. This interpretation of the
importance of total wetted area was assessed with a
similar stepwise regression using biomass of other fish
and total wetted area (F2,6 = 66.3, P = 0.0008, r2 =
0.96). Total wetted area explained 65% of the residual
variation in density of adult pikeminnow when re-
gressed against biomass of other fish.
Sediment dynamics
Depth of free space.-Total DFS monitored in strata
8 and 9 during 1996-2001 showed significant declines
in both runs and riffles (Fig. 6) corresponding to de-
clines in annual peak flow (Fig. 7). Mean annual total
DFS was positively correlated with peak discharge in
runs (P = 0.005, r2 = 0.86) and riffles (P = 0.03, r2
= 0.70) of stratum 8 and in runs (P = 0.02, r2 = 0.69)
and riffles (P = 0.04, r2 = 0.60) of stratum 9. Declines
occurred in both habitat types in both strata in years
following 1997, the last year when the thresholds for
widespread bed mobilization were exceeded. These de-
clines occurred despite thresholds for initial motion
having been exceeded in stratum 9 in 1998-2000 and
in stratum 8 in 1998.
1996 1997 1998 1999 2000 2001 1996 1997 1998 1999 2000 2001