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April 3 through April 16, 2006, Report No.
6
Waterford:
The Waterford trap sampled 9
out of 14 days between April 3 and April 16. A total of 83
juvenile Chinook salmon were captured, increasing the season
total to 8,082. Daily catch ranged from 2 to 19 Chinook
(Figure 1). Average forklength was 68.7 mm and ranged from
33 mm to 107 mm. Average weight was 4.6 g and ranged from
0.4 g to 7.9 g.
Figure 1. Chinook
salmon catch at Waterford versus flow at La Grange (LGN).
A 270 mm
O. mykiss was
captured on April 5 increasing the season total to two
(Figure 2).
Figure 2. A
270 mm
O. mykiss captured in the Waterford trap on April
5, 2006.
No trap efficiency tests were conducted at Waterford during
this sample period due to low catch numbers.
Due to safety concerns
associated with high river flows, sampling was suspended
at Waterford on April 12. At this site, the trap is
held in place by an overhead cable strung between two
large trees on opposite sides of the river. High river
flows created inadequate space to allow for safe
watercraft passage between the overhead cable and the
water surface; therefore, the overhead cable was removed
and the trap was temporarily secured in an area of low
velocity on the south bank. We immediately began
scouting for a new sampling location since flows are
expected to remain elevated for the remainder of the
season.
The most proximal
alternate site for sampling under high flow conditions
was identified just below the Hickman Bridge
(approximately two miles upstream of the original
sampling site) and the trap was moved to this location
on April 13. However, upon attempting to install the
trap at this location, we found that the water velocity
was too high for the trap to operate and the trap was
temporarily secured nearby in an area of low velocity.
The second closest site with potentially suitable
conditions was identified on April 14, and this location
is approximately four miles upstream of the original
site. We are currently seeking landowner permission to
secure the trap at this location and sampling will
resume as soon as permission is granted and the trap is
installed.
Grayson:
A total of 39 juvenile Chinook
salmon were captured at Grayson between April 3 and April
16, increasing the season total to 1,405. Daily catch
ranged from 0 to 16 Chinook (Figure 3). Average forklength
was 77.3 mm and ranged from 34 mm to 107 mm. Average weight
was 6.0 g and ranged from 1.4 g to 9.6 g.
Figure 3.
Chinook salmon catch at Grayson versus flow at Modesto (MOD).
No O.
mykiss were captured in the rotary screw trap during
this sampling period.
No trap efficiency tests were conducted at Grayson during
this sample period due to low catch numbers.
Figure 3.
High river flows at Grayson screw trap on
April 5, 2006.
Environmental Data:
Instantaneous water
temperature ranged between 48.0°F and 51.0°F at Waterford,
and between 52.0°F and 55.7°F at Grayson. Turbidity
fluctuated between 2.0 NTU and 15.9 NTU at Waterford, and
from 2.6 NTU to 75.6 NTU at Grayson. During the sampling
period, flows at La Grange ranged between 3,743 cfs and
7,747 cfs, while flows at Modesto ranged between 6,551 cfs
and 9,193 cfs.
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