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Yukon River Chum Salmon
Freshwater Ecology and
Environmental Influences On Their Survival:
Ongoing
research and analyzes
(continued)
Results
Smolt Survival (from PED
to smolt emigration)
In
Hodgin’s Slough the numbers of females spawning within the study site
have decreased each year; 174 in 1997, 146 in 1998, and 114 in 1999.
During 2000 we were unable to enumerate spawning females as extreme
flooding occurred on the 13th of August, just prior to peak
spawning. More than 90% of
spawning occurred prior to 30 August in previous study years (1997-1999).
Initial estimates of smolts originating within the study area are
55,000 for brood year 1997 and 27,000 for brood year 1998.
Smolt emigration estimates for the 1999 brood year were not
possible due to severe spring flooding during 2000.
Using the preliminary smolt estimate, the survival rates from PED
to smolt emigration were about 15% for 1997 and 8% for 1998 brood
years.
The
numbers of female chum using the Bluff Cabin Slough study site have varied
greatly: 107 in 1997, 6 in 1998, and 143 in 1999. Initial estimates of smolts originating within the study area
are 12,500 for brood year 1997, <300 for brood year 1998, and 27,900
for the 1999 brood year. The
1998 estimate is partial, as we had to suspend operations on the 17th
of May due to safety considerations.
Using the preliminary smolt estimates, the survival rates from PED
to smolt emigration were about 4.5% for 1997, 2% for 1998, and 10.5% for
1999 brood years.
Temporal and Spatial
Spawner Distributions
Spawning
at the two study sites is separated by two months.
Spawning chum salmon use restricted and relatively consistent areas
and habitat within the study sites.
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| Timing of chum salmon spawning in
the Hodgin's Slough and Bluff Cabin Slough study sites, 1997 -
1999. |
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| Distributions of chum salmon redd
locations in Hodgin's Slough study site, 1997 - 1999. |
Smolt
Survival (from redd pump sampling)
Attempts
to estimate actual egg deposition (AED) within the study sites using redd
pump sampling have not been tenable.
Estimates where made during the fall of 1997, however,
the resulting confidence intervals were essentially ±
the estimate. During the fall
of 1998 an Adaptive Sampling design was used in an attempt to improve AED
estimate precision. Although
adaptive sampling estimates done on small sample plots had improved
precision, it was apparent that an unacceptable level of destructive
sampling was needed to achieve this improvement (i.e., approximately 30 to
40% of the spawning area would have been sampled).
Redd pumping did provide useful survival estimates and development
stage (eyed-egg or alevin) indicated variation among habitat types.
At the Hodgin’s Slough site, survival rates to the eyed-egg stage
revealed higher survival in areas C and A compared to area F (see the
illustrations below). There
appeared to be a gradient in development with the majority of the eggs
already hatched in section C, about 50% in area A, and none in area F.
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Locations
of intergravel sampling strata (left).
These areas experienced varying degrees of spawning use.
Mean survival to eyed-egg stage with confidence intervals
(center). There were distinct differences in the numbers of eggs that
had hatched among the strata (right). |
Habitat
Characterization (using piezometers)
Measurements
in Hodgin’s Slough show large variation in hydraulic variables,
temperature, and DO. Relatively
distinct patterns were evident for temperature, DO and VHG.
In contrast, measurements taken in the Bluff Cabin Slough study
site indicated a more homogenous environment with the exception of VHG,
which appeared patchy. We are
performing further measurements and analyses for the calculation of
permeability and intergravel water velocity estimates.
Temperature and DO appear to match observed spawning distributions
best at the Hodgin’s Slough study site.
In areas of high spawner densities, intergravel late July
temperatures where higher (7 to 9.5°
C) and D.O was slightly higher (4 to 5.5 mg/l) than in areas of little or
no observed spawning where temperatures were 3 to 6°
C and DO was <2 to 4 mg/l. In
general, during winter the temperatures in the spawning areas were lower
(0.5 to 2°
C) than in non-spawning areas (1 to >2°
C). However, DO was
distinctly higher (>6 to 7.5 mg/l) in spawning areas than in
non-spawning areas (>1 to 6 mg/l).
In the Bluff Cabin Slough study site, temperatures varied little
between September and January (3.1 – 4.4°
C). Dissolved oxygen also showed little variation between fall (10.3 –
12.0 mg/l) and winter (9.5 – 11.0 mg/l) sample periods.
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Distribution
of dissolved oxygen (DO) and chum salmon redds (green circles) in
lower Hodgin’s Slough study site 1999.
Rows of black circles are piezometer locations. |
Survival of Eggs and Alevins (using in situ incubation baskets)
At
the Hodgin’s Slough study site, survival rates in spawning areas were 63
– 94% at the eyed-egg stage and 26 – 91% at the pre-emergent stage.
All but four of the 11 baskets in spawning areas were damaged
during spring flooding. In
these four baskets survival until emergence was 40 – 98%.
In non-spawning areas, where DO levels were low during the fall
(< 3 mg/l), survival to emergence was 0%.
In the Bluff Cabin
Slough study site survival until the eyed-egg stage ranged from 40 to
100%. Excluding the two
lowest basket survivals (40 and 63%), survival in the remaining 12 baskets
was very high (87 – 100%). Pre-emergent
survival was extremely low in the Bluff Cabin study site baskets (0 –
33%). Indeed, live alevins
were only found in two baskets (2% and 33% survival).
It appeared that the baskets in Bluff Cabin Slough had become
heavily silted.
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