Back
from the Brink: The Near-Collapse
of the Gerrard Trout Fishery
The legendary size and strength
of the Gerrard trout of Kootenay
Lake almost led to their demise
in the early 20th century, when
the British Columbia government,
looking for a lucrative revenue
source, began to sell Gerrard
trout eggs to buyers from around
the world. From 1916 to 1949,
eggs were collected from the trout’s
one and only spawning grounds
in the Lardeau River and shipped
as far as New Zealand and South
America. Although eggs were reared
at some nearby hatcheries, few
fry were released back to their
native waterway. At the same time,
sport fishing pressure on the
Kootenay Gerrard population was
heavy and unrestricted. Not surprisingly,
numbers of Gerrard trout in Kootenay
Lake dropped dramatically, and
in 1949, a count of spawners in
the Lardeau River revealed that
a mere 45 fish – including
only 22 females – were left
to perpetuate the unique Gerrard
strain. Furthermore, the trout’s
supreme sacrifice had mostly been
for naught: few transplant efforts
in other water bodies had succeeded.
(Despite many attempts throughout
the world, Jewel Lake and Lake
Pend Oreille, Idaho, are the only
water bodies outside of Kootenay
Lake in which Gerrard trout have
been successfully stocked.) Just
as the giant Gerrard was about
to fade into oblivion, the egg
harvest was halted. With regulated
sport fishing and other habitat
protective measures, Kootenay
Lake’s signature trout gradually
regained its historical spawning
run of about 1,000 fish.
|
|
The Ups and Downs
of the Kootenay Lake Kokanee
Q.: What do hydroelectric dams and plankton-eating
mysid shrimp have in common?
A.: Both have threatened the survival of
the native kokanee salmon population of
Kootenay Lake.
Kokanee are sockeye salmon that spend their
entire lives in freshwater. They are smaller
than sockeye (averaging about .5 –
1.3 kilograms in weight, compared to 1.8
– 2.3 kilograms for sockeye), but
are similar in shape and colouring. They
have a lifespan of 4 – 8 years, and
die after spawning. They live on plankton
and aquatic insects, and in turn become
food for larger fish such as Dolly Varden
trout, bull trout and cutthroat trout. In
Kootenay Lake, they are the food of choice
for the giant Gerrard strain of rainbow
trout.
For the past several decades, the Kootenay
Lake kokanee population has been inconsistent.
A series of surges, declines, and imbalances
between populations in the West, South and
North Arms of the Lake has been attributed
to a number of factors:
Mysid Shrimp Introduction
– In 1949, in a well-intentioned but
apparently misguided attempt to bolster
the flagging Kootenay Lake Gerrard rainbow
trout fishery, biologists stocked the Lake
with crustaceans known as “mysid shrimp.”
The shrimp had been identified as the major
food source of large rainbow trout in Alberta’s
Waterton Lakes. It was reasoned that the
transplanted food source could provide a
boost to the Kootenay Lake Gerrards.
About 10 years after the mysid shrimp introduction,
during the late 1950’s, sports fishers
noticed a sudden surge of trophy-sized kokanee
in the West Arm of Kootenay Lake. The salmon
were big and plentiful, and for several
years, recreational kokanee anglers flocked
to lakeside communities such as Balfour,
just east of Nelson. Eventually, however,
kokanee populations began to decline throughout
the Lake, and by 1990, the fish had all
but disappeared from the South Arm.
A similar pattern of kokanee surge and
decline following mysid introductions in
other lakes has led some biologists to speculate
that young kokanee – just-hatched
alevin and slightly larger fry – are
actually competing with the crustaceans
for plankton as their essential food source.
(The major food source for both young kokanee
and mysid shrimp is the zooplankton species
Daphnia, commonly known as the water flea.)
Furthermore, it is a competition in which
the crustaceans have the advantage: unlike
the kokanee, they feed both day and night,
they reproduce more quickly, have few predators,
and inhabit different zones of the lake.
Scientists suggest that the cycle which
led to the decline of the Kootenay Lake
kokanee population may have followed this
pattern:
• At first, kokanee size and numbers
surged because the large, mature kokanee
ate the newly-available mysid shrimp.
• As subsequent generations of kokanee
were produced, they had to compete at an
early stage for the most critical part of
their diet.
• As young kokanee lost ground against
the mysid shrimp, and starved or failed
to thrive, mature kokanee either reached
their lifespan or were fished out.
• Gradually, overall numbers began
to decline.
The recent increase in kokanee populations
in the West and North Arms of Kootenay Lake
– likely associated with lake fertilization
and spawning channel creation programs -
would seem to suggest that the Lake’s
population of mysid shrimp has lost its
competitive edge. But some researchers have
suggested that unusual water flow and temperature
conditions are only temporarily suppressing
the mysid shrimp population, and may be
masking an ongoing problem.
Hydroelectric Dams
– Following the construction of the
Duncan Dam on the Duncan River above Kootenay
Lake in 1967, and the Libby Dam in Montana
in 1974, nutrient levels in Kootenay Lake
began to decline. As critical nutrients
such as nitrogen and phosphorus were retained
in the Lake’s tributaries, zooplankton
density in the Lake decreased, followed
by a corresponding decline in each link
in the Lake’s food chain.
In the early 1990’s, when the kokanee
population of the Lake’s South Arm
appeared to be extinct, and numbers of kokanee
in the North Arm had dwindled to 5 - 7 million
fish and an “escapement,” or
spawning run of only 237,000 fish (about
1/5 of historical levels), the British Columbia
government, in conjunction with BC Hydro,
began an experimental program of lake fertilization.
Since 1992, liquid nitrogren and phosphorus
have been added to the lake in an effort
to restore the natural nutrient levels that
had been lost due to tributary impoundment.
Visit
the West Arm Kokanee Creek and
Redfish Creek Spawning Channels
Kokanee in the West Arm of Kootenay
Lake are a unique stock that
tend to be larger than kokanee
in the North and South Arms
of the Lake. Overfishing and
habitat destruction caused the
closure of the West Arm kokanee
fishery during the 1980’s,
but stocks have been boosted
in recent years by the construction
of 2 specially-designed spawning
channels. A popular West Arm
catch-and-release kokanee fishery
has now been opened.
The Kokanee Creek Spawning
Channel, built in 1985,
is located in Kokanee
Creek Provincial Park
on the north shore of Kootenay
Lake’s West Arm, 15 kilometres
east of Nelson. The Redfish
Spawning Channel is
located about 9 kilometres further
east, between the lakeside communities
of Nelson and Balfour.
At Kokanee Creek, visitors
can take part in a kokanee interpretation
program during the spawning
season of August and September.
Films, slide shows and channel
walks focus on the life history
of the kokanee. At Redfish Creek,
an information kiosk demonstrates
the life cycle of the kokanee,
and a footbridge leads to pathways
around the Channel. Look for
the bright crimson colour, hooked
jaws, and humped backs of the
kokanee males, as the fish gather
by the thousands (7,000 in Kokanee
Creek alone) to fulfill their
reproductive destiny. |
|
Under the direction of the Columbia Basin
Fish and Wildlife Program, a joint initiative
of BC Hydro and the British Columbia Ministry
of Water, Land and Air Protection, scientists
continue to monitor Kootenay Lake nutrient
and zooplankton levels, and to fine-tune
nitrogen and phosphorous supplementation.
(About 30 – 47 metric tonnes of fertilizer
appear to create optimum conditions.) Since
the fertilization program took effect, the
kokanee population of Kootenay Lake’s
North Arm has increased dramatically. By
2002, kokanee stocks in the Lake had recovered
to a near-historic level of 35 million fish,
with a spawning escapement of about 500,000.
Fisheries managers are working toward a
target of 750,000 spawners, while maintaining
a total kokanee population of 25 –
35 million fish.
Habitat compensation has also been part
of the Kootenay Lake kokanee restoration
effort. The Meadow Creek Spawning
Channel, built on the Duncan River’s
most productive kokanee tributary in 1967,
provides ideal habitat for 300,000 –
350,000 spawners.
To date, kokanee numbers in the South Arm
of Kootenay Lake remain low, with a spawning
escapement of only 5,000 fish. Nutrient
retention caused by the Libby Dam on Montana’s
Kootenai River continues to have an impact
on Kootenay Lake kokanee.
The restoration of kokanee abundance in
other areas of Kootenay Lake, however, has
had positive effects on the Gerrard trout
fishery. (The genetically large strain of
rainbow trout derives its strength from
a premium diet of Kootenay kokanee.) Other
fish that reap the benefits of kokanee conservation
are bull trout, white sturgeon and burbot. |
