Third time a charm? Sturgeon strategy
altered
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May 11, 2013 |
Flows sent down from northwest Montana’s Libby
Dam with the intent of benefiting endangered
Kootenai River white sturgeon will take a new
shape this year in an ongoing attempt to lure
the big beasts away from badly functioning
spawning areas and onto gravelly river bottoms
believed to be prime habitat for reproduction.
A double-peak strategy submitted this week by
the U.S. Fish and Wildlife Service and approved
for implementation by the U.S. Army Corps of
Engineers will be the third flow manipulation
strategy employed since the 2006 Kootenai River
white sturgeon biological opinion was released
in 2006.
Endangered Species Act BiOps assess whether
federal actions, such as the existence and
operation of Libby Dam, jeopardize the survival
of listed species, such as the Kootenai sturgeon
and bull trout in that river system.
BiOps often include prescriptions – reasonable
and prudent alternatives – for improving the lot
of the affected species. Among the requirements
in the 2006 BiOp issued by the USFWS are
requirements for minimum volumes of water to be
released to augment flows for sturgeon in
springtime, when natural flows historically rose
to a peak called the freshet. That sturgeon
volume depends on the anticipated volume of
spring runoff.
Natural flows changed as a result of Libby Dam,
which was built in the 1970s. Flood control and
power production operations are believed to be
one of the reasons for a considerable decline in
white sturgeon reproduction and, as a result,
the overall population.
Initial efforts to provide a several days-long
“pulse” of water in 2008 and 2009 were deemed
unsuccessful at changing the sturgeon’s spawning
behavior, with most activity still taking place
in silt-bottomed areas downstream of Bonners
Ferry instead of gravel beds upstream more
likely to produce successful spawning and
production of juvenile sturgeon. Those
operations stayed within the dam’s powerhouse
capacity.
That lack of success triggered a three-year
experiment called for in the BiOp that pushed
the pulse volume up from powerhouse capacity of
about 25,000 cubic feet per second to 35 kcfs,
which included an additional volume of up to 10
kcfs sent through spill gates. The Corps
operates Libby Dam.
“Telemetry data for spawning Kootenai sturgeon
females from 2010-2012 indicate that the spill
tests did not facilitate a change in Kootenai
sturgeon spawning and migration behaviors. Given
the results from 2008-2012 sturgeon operations
at Libby Dam, a different approach to managing
the sturgeon volume is warranted,” according to
a system operation request presented by the
USFWS’ Jason Flory Wednesday to the Technical
Management Team.
The TMT includes representatives of federal,
state and tribal hydro and fish management
entities. They meet to consider dam operational
operation that might be implemented to improve
fish survivals.
“The objective of the 2013 sturgeon augmentation
operation described in this SOR is to provide
two periods of peak river stages/flows during
the spring run-off period.
“The first peak, timed to low-elevation run-off
below Libby Dam, is intended to provide sturgeon
cues to begin upstream migration and staging.
“The second peak, timed to high-elevation
run-off above Libby Dam, is intended to provide
sturgeon cues to migrate further upstream from
their staging areas and spawn towards the end of
the second peak and/or on its descending limb.
“Overall, the goal is to provide conditions that
will enable sturgeon to migrate to, and spawn
over, rocky substrates that exist upstream of
Bonners Ferry,” the SOR says.
“We’re tying other things, flow-wise, to see if
we can affect a change” in sturgeon spawner
behavior, Flory said.
“We need these fish to spawn in gravel,” whether
that means bringing fish upstream, or bring
gravel to the downstream areas where the
sturgeon have been spawning, Flory said.
The placement of suitable spawning substrate in
downstream spawning areas is part of an
ambitious habitat restoration led by the
Kootenai Tribe of Idaho and outlined in its
Kootenai River Habitat Restoration Master Plan.
Each of the peaks is expected to last up to a
week. The first would be triggered when a
regional team of biologists determines that
local tributary run-off at lower elevations
downstream of Libby Dam is peaking.
Outflow volumes would be held at 20-25 kcfs for
5-7 days without using spill, which stirs up
totaled dissolved gas that can be harmful to
resident fish downstream of the dams.
Outflows would then backed off to levels that
allow the maintenance of at least 18 kcfs at
Bonners Ferry. The Kootenai River is nearly 450
miles long. Beginning in British Columbia,
Canada, the river flows through northwest
Montana and northern Idaho, and then turns
northwest back into British Columbia.
Increased discharge from Libby Dam would begin
again up to full powerhouse capacity when the
team of biologists determines that the
high-elevation run-off in the Kootenai Basin has
begun.
“Actual peak discharge during this second peak
will depend on local conditions (i.e. river
stage at Bonners Ferry).
“Selective withdrawal gates at Libby Dam above
elevation 2,326 mean sea level will be placed to
within 30 feet of the surface of the reservoir
prior to the end of the second peak, described
above, allowing for release of warmer surface
water as the receding limb of the hydrograph
commences,” the SOR says.
“Release of warmer water from Libby Dam, in
combination with lower volume of release, will
allow the Kootenai River temperature to increase
to appropriate spawning temperatures at Bonners
Ferry (8-10 degrees C) during the receding limb
of the hydrograph.”
The first pulse could start as early as this
weekend, the Corps’ Adam Price said. Warmer than
normal temperatures have prevailed and were
forecast to continue. That has hastened snowpack
meltdown.
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