7908

• UCREFRP Catalog Number: 7908
• Author: Valdez, R. A. and R. J. Ryel.
• Title: Life History and Ecology of the Humpback Chub ‎(
• USFW Year: 1995.
• Copyright Material: NO

Final Report

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Fig.7. Monthly geometric mean catch per effort, CPE (GMCPE
#fish/100 ft/100 hr) for adult humpback chub captured in nets
within RM 60.0-61.9 (LCR Inflow), 1991-93. Standard error
bars are shown.

and ramping rate. Adult radio-tagged humpback
chub were more active and in shallower water at
night and during the daytime when river turbidity
was high (NTU>30). Adults used deep water (>4.5
m) more frequently during the day, particularly in
clear water conditions. Catches of subadults
indicate that this life stage exhibited similar
photosensitivity. Movements during low light

conditions were attributed to the use of
turbidity as cover from predators and to
increased feeding activity from increased loads
of suspended and drifting material.

Movement by adults was greater during high
magnitude discharges and during highest
ramping rates, probably in response to
changing river hydraulics or to increased drift
food availability, or both. The proportion of
times that adults moved was significantly
greater when flows were above 10,000 cfs,
although the greatest movement occurred
during increasing flows or decreasing flows.
Movement was reduced when flows stabilized
at higher magnitudes (Fig. 8). The proportion
of times adults moved was also greater when
local ramping rates (measured at the nearby
LCR USGS stream gage) were greater than
300 cfslhr during a full range of flow
magnitudes, although this movement was
significantly greater only at flows above
10,000 cfs. The fish probably moved in
response to changing hydraulic characteristics
(e,g., water velocity, depth, current direction),
as well as to increases in drift food items.
Densities of drifting macroinvertebrates
increased during descending flows and volume
of Cladophora glomerata (dominant green
algae) increased during ascending flows.

Movement of sub adults (<200 mm TL) was
attributed primarily to downstream dispersal
resulting from unstable shoreline habitats and
cold mainstem temperatures. This movement
was deduced from reduced densities of
sub adults between the LCR (RM 61.3) and
Hance Rapid (RM 76.6). We believe that this
dispersal resulted from a combination of
destabilized shoreline habitats (caused by daily
flow regulation) and reduced swimming ability
of young fish (caused by cold water
temperatures); laboratory tests (Bulkleyet al.
1982) showed a 98% reduction in fatigue time
of juvenile humpback chub in 0.51 mps velocity
water at 200C (85 min) compared to water at 140C
(2 min). It was hypothesized that displacement of
sub adults from sheltered shorelines exposed these
fish to predation, increased their energy expenditure
in fmding new habitat, and transported young into
reaches with little shoreline habitat, such as the
Inner Gorge. The combination of cold water