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March 29 through April 17, 2005, Report No.
1
As in
previous years, tandem rotary screw traps were installed in
the Tuolumne River near Grayson (RM 5). The traps were
installed between March 29 and April 1, 2005. The traps
sampled for only one night before the anchoring points on
both the north and south banks began to fail
from the force caused by high flows (>7,000 cfs) in
combination with the saturated ground. The traps
were temporarily raised while we determined how the traps
could be secured to each bank
while withstanding the force of high flows. A couple
of large trees were located on
each bank approximately 75 yards downstream from the
original trapping site. The traps were secured in the new
location on April 5 and began sampling immediately.
Chinook
The traps sampled 13 out of 17
days between April 1 and April 17 capturing a total of
40
juvenile Chinook.
Daily catch ranged from 0 to 8 Chinook (Figure 1).
Average forklength was
86.6 mm
and ranged from
51 mm to 98 mm. No O.mykiss were captured during the
sampling period.
Figure 1. Chinook
Catch at Grayson versus flow at Modesto.
Other species
A total of 11 non-salmonid species
were captured in the traps during the sampling period
including Bluegill, Golden shiner, Hardhead, Lamprey, Mosquito
fish, Inland silverside, Redear sunfish, Red shiner,
Sacramento pikeminnow, Smallmouth bass and White catfish. Of these,
Sacramento pikeminnow (n = 30) were the most
abundant individuals captured and were 34 mm to 76 mm in length.
The next most abundant non-salmonid
species was White catfish (n =12) that measured between 42 mm and
117 mm.
Daily catch of other non-salmonids species ranged between 1
and 6 individuals.
Environmental Data
Environmental
conditions fluctuated throughout the sampling period due to
increased releases from Don Pedro for flood control purposes.
Instantaneous temperature at Grayson fluctuated between
48° F and 55° F and turbidity
ranged from 2.7
NTU to 4.4 NTU.
During the
sampling period, flow at La Grange Dam (LGN; RM 52.2)
ranged between 3,991 cfs and 7,370 cfs.
Flows at Modesto (MOD; RM 16.3)
ranged from 4,268
cfs to 6,919 cfs.
Note: The next summary will cover a three-week
period and will be distributed the week of May 8, 2005.
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