Kootenai River burbot nearing extinction
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March 13, 2014 |
A once thriving fishery, the wild Kootenai River
burbot – freshwater cod – is nearing extinction
if it doesn’t get help, according to a
scientific summary of the burbot in this river
that spans two states and British Columbia.
The burbot population in the river was estimated
at 150 fish in the mid-1990s and had declined to
only 50 fish in the early 2000s. With annual
mortality estimated at 63 percent, the wild
stock would reach extirpation by 2015. The
culprit is Libby Dam and how the dam has been
operated since it was built in 1972.
Although there is no new attempt in the works to
list the Kootenai River burbot under the U.S.
Endangered Species Act (an attempt was made in
2000 to list the fish as threatened, but that
petition was denied because the fish did not
represent a distinct population segment), Idaho
Fish and Game, the Kootenai Tribe of Idaho, the
British Columbia Ministry of Environment and the
University of Idaho Aquatic Research Institute
have signed on to a conservation strategy aimed
to bring the burbot back to a sustainable and
harvestable population.
“All of the parties involved are committed to
working together to ensure that burbot once
again thrive as a population (given the current
river constraints),” said Ryan Hardy, principal
fishery research biologist at IDFG, and one of
the summary’s authors. “The conservation
strategy is in place and should be instrumental
in our efforts to rehabilitate a viable
population.”
The strategy includes recovery targets,
replacing nutrients in the river and
conservation aquaculture in the mainstem and
tributaries to supplement the wild stock during
rehabilitation, but has yet to include
significant changes to Libby Dam’s operations
during the critical spawning period in December
through February.
“A Synthesis of Kootenai River Burbot Stock
History and Future Management Goals” appeared in
the November 2013 “Transactions of American
Fisheries Society” in a special section on
burbot in the Kootenai River and elsewhere in
the United States. The synthesis http://dx.doi.org/10.1080/00028487.2013.790845
is by Hardy and Vaughn L. Paragamian, also a
fisheries biologist at IDFG.
In Idaho, burbot appear only in the Kootenai
River and were at one time an important winter
fishery for Native Americans and early
Europeans. This and the fishery in Kootenay Lake
in British Columbia “may have been the most
robust burbot fisheries in North America.” But
the fishery declined rapidly after the
construction of Libby Dam by the Army Corp of
Engineers and by 1992 it had closed completely.
The fishery eventually also collapsed in the
Kootenay Lake and Kootenay River in British
Columbia.
The Kootenai River is the second largest of the
Columbia River tributaries. Its multi-national
and roundabout journey to the Columbia River
begins in Kootenay National Park in southeast
British Columbia, flows south into northwest
Montana where Libby Dam is located and forms
Lake Koocanusa. From there the river flows into
the Idaho panhandle, back north into British
Columbia to form Kootenay Lake and finally flows
into the Columbia River at Castelgar, British
Columbia.
Burbot were present in the entire river prior to
the construction of Libby Dam, but as two
strains. Those above Kootenai Falls (downstream
of Libby Dam) are from the Mississippi clade and
below the falls the burbot are of the Pacific
clade.
The dam has been operated for hydropower
production and flood control, impacting the
river’s food supply, its temperature and the
amount of water released, particularly during
the winter when burbot spawn. Higher than normal
water temperature and flows from the dam during
crucial spawning months have been identified as
the major limiting factor on burbot spawning.
Add overfishing and the Kootenai River burbot
are now near extinction.
One sign of the poor spawning conditions is
proportional stock density. Over 46 years
biologists have documented an increase in the
length of the fish, but with very few young fish
entering the population. The average burbot
increased in length from 459 millimeters in
samples taken in 1957-58 to 615 millimeters in
2002-04 samples. It’s apparent that fewer young
burbot are surviving the river’s conditions.
Studies of dam discharges “determined that high
winter discharges (especially during power
peaking) disrupted the spawning movements of
burbot” and in many cases the high discharges
forced burbot back downstream. The fish tend to
have a low swimming endurance and discharges
from Libby Dam in excess of 300 cubic meters per
second inhibit spawning migration. Burbot prefer
discharges that are less than 176 cubic meters
per second.
Temperature also makes a difference. Higher
winter discharges also carry higher water
temperatures.
All the while, Koocanusa creates a nutrient
trap, thus reducing the nutrients in the river
below the dam. That has had a negative impact on
rearing and overall survival downstream.
IDFG and the Kootenai Tribe of Idaho have added
nutrients to both the Kootenai River and
Kootenay Lake since 2005. That has been shown
“to dramatically increase all levels of the food
web, including fish populations that feed
directly on macroinvertibrates and diatoms.”
Without an ESA listing, fisheries managers have
turned to the conservation strategies to restore
the burbot population. Hardy said that it’s
reasonable to lay out such strategies when a
species is in peril, but not listed under the
ESA.
The interim recovery target for burbot abundance
is 5,500 age 4 and older fish within 25 years
and the ultimate target is 17,500 fish. Much of
this will be accomplished through supplementing
the wild population.
Following specific protocols, the University of
Idaho Aquaculture Research Institute and the
Kootenai Tribe of Idaho began stocking in 2009
with 209 larval fish stocked, scaling up to
400,000 larval and juvenile burbot in 2012.
Hoop-net sampling by the IDFG indicate that
these stockings have been successful. In
addition, multiple locations, including
historical spawning tributaries, are included in
the stocking protocol in order to determine
which strategy works best for survival.
Still, the survival of hatchery fish is not
thought to be the final solution to the spawning
failure of wild burbot, Hardy said, but the
hatchery releases and their survival will
provide valuable information to determine the
potential changes that should be made regarding
flow and temperature management at Libby Dam,
the final step in the conservation strategy.
“At this point, Libby Dam operations in the
winter are not specifically managed for burbot;
rather, they are largely based on energy needs,”
Hardy said.
Past research suggests that burbot spawning
migrations may be disrupted by large
fluctuations in winter discharge. Although
considered sound science, this research was
limited to active tracking technology and a
limited number of fish from which to draw
specific conclusions, Hardy said.
Since then, the technology of sonic telemetry
has advanced, and the number of adult fish that
has been tagged in the Kootenai River to aid in
evaluating the fluctuating flows has now
substantially increased.
According to Hardy, in order to build upon this
past research and draft a specific system
operation request that will be conducive to
spawning, biologists are monitoring fish through
multiple spawning periods with a passive sonic
tracking array that should give a much more
refined understanding regarding effects of
present flows and temperatures on spawning.
That SOR will likely include flows less than 176
cubic meters per second and temperatures below 4
degress centigrade during the 40-day incubation
period in order for eggs to successfully hatch. |
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