This report summarizes
our activities and results for 1993, and it is our final report of
this three year study. The objectives of this study were as follows:
1) to determine
the source(s) of losses (or errors in accounting) for adult fall
chinook salmon . between Ice Harbor (IHR) Dam and Lower Granite
(LGR) Dam, and upstream of LGR in the Snake River;
2) to identify
spawning locations upstream of LGR to assist with calibration of
aerial redd surveys, redd habitat mapping, carcass recovery (for
genetic stock profile analysis), and correction of estimated adult/redd
ratios; and
3) to estimate
passage and migration times at Snake River dams and reservoirs.
We targeted unmarked
adult fall chinook salmon for trapping and radio tagging at IHR and
LGR Dams as they ascended the Snake River during their spawning migration.
We used aerial, fixed-site, and ground mobile radio tracking to determine
the movements of these fish.
Two hundred fall
chinook salmon were radio tagged and released near IHR Dam in 1993.
All fish were released 2.2 km upstream’of IHR Dam at Charbonneau
Park (CHAR). We were able track or relocate 190 (95%) of the fish
away from CHAR. Fifty-nine (3 1 .O%) fish descended downstream to
below IHR dam (fell back at IHR) without crossing Lower Monumental
Dam (LMO). Many of these fish were detected in the Columbia or Yakima
Rivers, although some were detected as far downstream as the John
Day River in Oregon. Another 128 salmon (66.8%) initially passed upstream
of LMO Dam without previously falling back at IHR Dam. Only 80 (42.1%)
radio tagged salmon initially passed Little Goose Dam (LGO) without
previously falling back at a downstream dam. Sixty-six (34.7%) of
these fish passed LGR Dam. Many of the fish that fell back reascended
the dams. A total of 72 radio tagged salmon that were released at
CHAR passed upstream of LGR Dam, including fish that had fallen back
and reascended a downstream dam.
Over 80 percent
of the radio tagged salmon that entered Lyons Ferry Hatchery each
year had reached LGO Dam before descending to the hatchery. Extensive
wandering was documented between LMO and upstream of LGR before salmon
entered Lyons Ferry Hatchery or the Tucannon River. In 1993, forty-one
radio tagged salmon were found to be of hatchery origin when recovered
and analysis of marks and scale samples were completed. These fish
entered Lyons Ferry Hatchery with similar movements to unmarked salmon.
Each year a few radio tagged salmon have remained near the hatchery
without entering, which suggests the hatchery may have inadequate
attraction flows.
Radio tagged
fall chinook passed lower Snake River dams in 2-5 days each, on average.
Median travel times through LMO and LGO reservoirs were 1 .O- 1.3
days each, which was slower than travel times for spring chinook or
steelhead in the Snake River in 1993 (Bjornn et al. 1995).
We documented
losses or accounting errors of 38 percent for radio tagged salmon
between IHR and LGR Dams. Our radio telemetry data suggests that 83
percent of the fish unaccounted for (loss) between these two dams
can be attributed to fall back at IHR Dam in 1993. The loss explained
by fall back between IHR and LGR was 62 percent in 1992. All but 3-6
percent of this loss is from fall back before fish crossed LMO Dam.
We supplemented
radio tagged fish upstream of LGR by radio tagging and releasing another
20 salmon at that dam. We combined radio tagged salmon from both dams
to examine fall back, accuracy of ladder counts, pre-spawning mortality
and spawning location upstream of LGR for radio tagged salmon.
Fall back was
common for salmon tagged either at IHR or LGR Dams. Some fish fell
back, reascended, and fell back again at the same dam. Other salmon
fell back at multiple dams. Untagged fall chinook salmon also fell
back at LMO, LGO, and LGR Dams on the Snake River, as well as from
McNary Dam (e.g., Wagner et al. 1992). We documented more fall back
during all three years than Bjornn et al. (1995) has reported for
spring/summer chinook salmon in the Snake River. Apparently, at least
74 percent and 86 percent of the salmon that fell back survived in
1993 and 1992, respectively, even though the primary fall back route
was through the turbine intakes at all dams.
We documented
frequent interchange of fish from the Snake River upstream of LGR
with the Grande Ronde, Clearwater, and Salmon Rivers. Most spawning
appeared to be in the Snake River between Asotin and the Grande Ronde
River. Adult/redd ratios have been reduced from 6-10 to 3-5 by accounting
for fall back at LGR and pre-spawning mortalities, along with improved
redd counting methods. Tailrace spawning could not be determined by
using radio telemetry because of the erratic fish movements and our
inability to determine when spawning occurred for radio tagged fish.
Determining the
number of salmon available to spawn upstream of a dam was complicated
by fish that fell back or reascended a dam, extensive erratic fish
movements to and from several different rivers, and our inability
to ascertain the fate of each radio tagged salmon. For example, we
estimate that salmon counts at LGR Dam were higher than the number
of salmon available to spawn by 3 1 percent in 1993 and 54 percent
in 1992. Consequently, fish counts should be adjusted to account for
fall back and pre-spawning mortality. Otherwise, fish counts provide
an overestimate of the number of fall chinook salmon available to
spawn in the Snake River.
