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Once nearly gone, Lake Pend Oreille kokanee have
rebounded in a big way--over one million fish |
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From the Columbia Basin Bulletin |
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July 19, 2014 |
The Lake Pend Oreille kokanee population has
literally risen from its death bed over the past
eight years, due in large part to an Idaho
Department of Fish and Game strategy aimed at
reducing predation on the smallish game fish.
“We were right on the ragged edge of losing the
kokanee population” in the large north Idaho
lake, Jim Fredericks, the IDFG’s Panhandle
Region fishery manager told the Northwest Power
and Conservation Council’s Fish and Wildlife
Committee during its July 8 meeting in Portland.
A population that had into the 1990s commonly
provided harvests of a million fish annually
began to shrink. State fishery officials were
forced to close the fishery beginning in 2000.
The low point: an estimated abundance of only
9,994 adult fish in 2007. The declining trend
was roughly mirrored by a rapid surge in the
lake trout population in Lake Pend Oreille, a
long-lived, large bodied fish that preyed
heavily on the kokanee.
The kokanee, a non-native species, were a prized
angler target that also provided food for native
bull trout, which are now protected under the
Endangered Species Act, as well as introduced
Gerrard rainbow trout and lake trout. The latter
two species grow to trophy size.
Kokanee became established in the lake in 1930s
and became a keystone species -- historically
supporting the most popular fishery in Idaho and
serving as prey for other valued fish species.
The Gerrard rainbow trout were introduced in
1941. Lake trout were introduced in 1925 but
remained at extremely low abundance until
late-1990s.
Now the trends have reversed. A large-scale lake
trout suppression program launched by the state
in 2006 has resulted in the removal of 165,000
lake trout.
More than 75,000 lake trout have been removed by
anglers motivated by a $15 reward per fish.
Another 89,000 have been taken from the lake via
an extensive netting effort using contracted
commercial fishermen from Lake Michigan.
The kokanee recovery effort has largely been
funded – at a rate of about $1 million per year
-- by the Bonneville Power Administration
through the NPCC’s fish and wildlife program.
Avista Corporation has also provided funding.
BPA markets power generated at the U.S. Army
Corps of Engineers’ Albeni Falls Dam, which
controls the elevation of Pend Oreille. Avista
owns hydro projects upstream of the Pend Oreille
on the Clark Fork River, the lake’s main
tributary.
Dam manipulations are factors that can affect
kokanee and other fish and wildlife populations.
The commercial adult lake trout catch rates have
plummeted 82 percent from 2006 to 2013, an
indication of a severe population decline. And
juvenile catch rates have dropped by 83 percent.
Meanwhile the estimate of kokanee adult
abundance jumped to 1.3 million in 2013. And the
estimated kokanee biomass in the lake more than
doubled just from 2012 to 2013. The 2013 biomass
total of 625 metric tons is up from the
population’s low point of 74 tons in 2007.
The rising kokanee population trend prompted
IDFG officials last year to open the first
kokanee fishery in the lake since 1999, albeit
with a six-fish daily bag limit. With positive
expectations, that bag limit was raised to 15
fish this year.
After surveys of the lake were conducted in late
summer of 2013, biologists estimated that the
2-year-old-going-on-3-year-old age group was
“even larger” than the one that produced this
year’s adult group. The surveys are conducted by
trawling the lake to sample both older fish and
fry, and through the use of hydrocoustics, which
use SONAR technology to identify objects
underwater.
Adult fish are mature kokanee, meaning fish that
are going to spawn that year. Hatchery fish
mostly mature at 3 years old, while wild fish
typically mature at age-4,” according to IDFG
biologist Andy Dux. “Anglers are catching almost
entirely age-3 and age-4 kokanee.”
And they are doing well.
“Last year people were easily catching their
six-fish limit,” Dux said. This year they are
reeling in the 15-fish limit within a couple
hours.
Fredericks told the Council that the lake trout
suppression is working to achieve a variety of
goals. The reduced predation has helped fuel the
increase in the kokanee population in the lake.
In addition the bull trout population appears to
be stable or increasing, likely helped by the
reduced predation threat and expanded kokanee
prey.
Rainbow trout growth rates have also been
increasing.
Pend Oreille, located in the northern panhandle,
is Idaho’s largest and deepest lake.
Frederickson said it is also one of the deepest
lakes in United States with an average depth of
538 feet (164 meters) and a maximum depth of
1,152 feet (351 meters). |
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