Northwest Fisheries Science Center released its annual survival estimate of
juvenile salmon and steelhead that migrated through Snake and Columbia river
dams, finding that one particular river reach was less friendly for the fish
is the reach from McNary Dam to John Day dam, which for yearling chinook,
survival was the lowest on record.
information was delivered in a September 18, 2017 memo from Rich Zabel,
director of the Fish Ecology Division at NOAA, to Ritchie Graves, chief of the
NOAA Fisheries' West Coast Region Columbia River Hydropower Branch.
memo, “Preliminary survival estimates for the passage of spring-migrating
juvenile salmonids through Snake and Columbia River dams and reservoirs, 2017,”
is at http://pweb.crohms.org/tmt/agendas/2017/1004_2017_Preliminary_Survival_Estimation_Memo.pdf.
the study, which was funded by the Bonneville Power Administration, NOAA
PIT-tagged 22,049 hatchery steelhead, 18,422 wild steelhead and 14,241 wild
yearling chinook salmon. All were released into the tailrace of Lower Granite
Dam, the upstream of the four lower Snake River dams. NOAA has produced the
survival estimate study since 1993.
study estimates survival of both hatchery and wild yearling chinook, survival
of both hatchery and wild steelhead and survival of hatchery and wild sockeye
salmon in lower Snake River reaches through Bonneville Dam as well as from Rock
Island Dam through Bonneville. It also estimates the percentage of migrating
fish in the lower Snake River that were transported by barge and summarizes
environmental conditions, such as flow, spill and water temperature.
also estimated survival of yearling chinook hatchery fish from seven Snake
River hatcheries upstream of Lower Granite. The mean survival in 2017 from the
hatcheries to Lower Granite was 65 percent. While lower than the past three
years, the mean for the period 1998-2017 is 65.1 percent (the range has been
49.4 percent in 1997 to 71.7 percent last year).
in 2017 downstream of Lower Granite for yearling chinook (both hatchery and
wild) was nearly average at 91.6 percent (average is 92.5 percent) in the Lower
Granite to Little Goose reach and survival in the Little Goose to Lower
Monumental reach was 90.8 in 2017 (average is 92.2 percent). Survival was above
average at 91.2 percent (average is 86.3 percent) in the Lower Monumental to
McNary reach and John Day to Bonneville reach (2017 was 87.1 percent, average
is 80.9 percent), the study says.
because the estimated survival in the McNary to John Day reach (2017 was 72
percent, average is 86.5 percent) was the lowest on record, the estimates
resulted in above average survival from Lower Granite to McNary, but below
average survival in the remaining combined reaches through Bonneville.
mean estimated survival for yearling chinook salmon from Lower Granite Dam
tailrace to McNary Dam tailrace was 74.3 percent (average is 73.6 percent) and
from McNary to Bonneville it was 64.3 percent (average is 70 percent).
estimated survival for yearling chinook from Lower Granite to Bonneville was
47.8 percent, while the average over the years 1999 – 2017 was 52.4 percent.
2016 estimate (Lower Granite to Bonneville) was 50.5 percent. Survival through
the power system has remained relatively stable since 1999, NOAA says, with the
exceptions of lower estimates in the low flow years of 2001 (27.9 percent),
2004 (39.5 percent) and 2015 (42.8 percent).
focus in on the wild yearling chinook from the Snake River, the mean estimated
survival from Lower Granite to McNary was 70.9 percent, but dropped
significantly to just 43.6 percent from McNary to Bonneville.
survival for wild yearling chinook from Lower Granite to Bonneville tailraces
was 30.9 percent.
for combined hatchery and wild Snake River steelhead was above average in all
of the individual reaches except for John Day to Bonneville.
(75.9 percent) was above average (65.3 percent) from Lower Granite to McNary,
but below average (2017 was 60.5 percent, average is 67.4 percent) from McNary
Granite to Bonneville (45.9 percent) was close to the average (46.3 percent).
The 2016 estimate was 44.4 percent.
is the third consecutive year with below average survival for Snake River
steelhead after seven consecutive years of survival estimates above the mean,
in on just the wild steelhead, survival from Lower Granite to McNary was 72.3
percent, McNary to Bonneville was 41.3 percent, and Lower Granite to Bonneville
was 29.9 percent.
sockeye salmon juvenile survival estimate from Lower Granite to Bonneville for
the combined hatchery and wild fish was 17.6 percent, the fourth lowest
survival estimate from 1998 to 2017.
is the third consecutive year that juvenile Snake River sockeye survival has
been below the average of 39.2 percent. 2016 survival was estimated at 11.9
percent and 2015 was 37.3 percent. The highest survival was 82 percent in 2008.
for upper Columbia River sockeye, the juvenile survival estimate from Rock
Island Dam to Bonneville was significantly higher at 50 percent, which was
still slightly below the average of 50.3 percent and is a highly uncertain
estimate, but mortality was not nearly so high as that for Snake River sockeye,
for hatchery yearling chinook from the upper Columbia River cannot be estimated
for reaches upstream of McNary Dam. However, their survival from McNary to
Bonneville was 94.4 percent, which is above the average of 81.8 percent.
steelhead survival from the upper Columbia River was 96.4 percent from McNary
to Bonneville, which is above the average of 74.7 percent. However, NOAA says
the estimate has “high uncertainty.”
arrived earlier in the season than normal. When transportation began May 2 at
Lower Granite, Little Goose, and Lower Monumental dams, about 70 percent of
wild yearling chinook and 53 percent of hatchery yearling chinook had already
passed. The average in years 2006-2014 was 42 percent for wild and 31 percent
for hatchery yearling chinook
addition, about 60 percent of wild steelhead had already passed Lower Granite
when transportation began, far more than the average of 29 percent. Some 63
percent of hatchery steelhead was estimated to have passed the dam before May
2, also higher than the average of 33 percent.
17.8 percent wild spring-summer smolts were transported, while 21.6 percent of
hatchery spring-summer smolts were transported. Some 23.3 percent of wild
steelhead and 20.9 percent of hatchery steelhead were transported.
temperatures were about average, but river flows and spill were far above
average during the migration season (April 1 to June 15).
the period, Little Goose flows averaged 138,700 cubic feet per second, far
higher than the 1993 – 2017 daily mean of 91.8 kcfs. Only 1997 had a higher
daily mean flow. Mean water temperature at the dam during this period was 11.2
degrees Celsius (52.34 degrees Fahrenheit). The long-term mean is 11.3 C.
at Snake River dams at 63.7 kcfs mean and far above the long-term mean of 27.2
kcfs was the most spill during the time period 1993 – 2017.
as a percentage of flow averaged 44.5 percent, again far above the long-term
mean of 26.8 percent. It was the highest mean spill percentage during the time
flows and spill resulted in shorter travel times, April through June, for all
fish than in any other year (1998 – 2017).
October 7, 2016, “Report Details 2016 Juvenile Salmon/Steelhead Survival In
Snake/Columbia; Snake Sockeye Take A Hit,” http://www.cbbulletin.com/437701.aspx