Shrimp stocking, salmon collapse, and eagle displacement' Craig Spencer, Riley McClelland, and Jack

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Shrimp stocking, salmon collapse, and eagle
displacement. Craig Spencer, Riley McClelland,
and Jack Stanford. 1991. BioScience 4114-21.
(on the web page)
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McDonald Creek. A 4 km section in Glacier
National Park between Lake McDonald and the
Flathead River.
Flathead Lake -- about 100 km downstream from
McDonald Creek
On of the largest freshwater lakes in US, about
30 miles long and 10 miles wide. Over 100 m
deep. Formed by glacial damming.
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Mysis relicta, Opossum shrimp Native to deep
lakes in north central North America and
Sweden. Predaceous on zooplankton. 1 -2 cm long
Introduced into Kootenay Lake, BC, in
1949 Resulted in a dramatic increase in growth
of Kokanee salmon Stocked in 100 lakes in NW US
and Canada Into Flathead Lake in 1981
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Oncorhynchus nerka, landlocked sockeye
salmon Introduced into Flathead Lake in 1916.
Became the dominant sportfish. Over 100,000
caught per year. Potadromous -- Swim up the
Flathead River and spawn in McDonald Creek
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Bald eagles, Grizzly bears, coyotes, gulls, fed
on the spawning salmon. As many as 639 eagles.
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What happened as a result of opossum
introduction? 1. Zooplankton population
decreased
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Copepods
Cladocerans
Zooplankton abundance in Flathead Lake in 1972-73
(pre-Mysis) and 1988 (post-Mysis).
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What happened as a result of opossum
introduction? 1. Zooplankton population
decreased 2. No increase in phytoplankton
production. Flathead Lake is an
ultra-oligotrophic lake and is bottom-up
regulated by nutrients (at least for now). 3.
Salmon population crashed. 1979-1985 26,000 to
118,000 spawners 1987 330 1989 50
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Mean shrimp, salmon,and eagle abundance in
Flathead Lake and McDonald Creek.
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What happened as a result of opossum
introduction? 1. Zooplankton population
decreased 2. No increase in phytoplankton
production. Flathead Lake is an
ultra-oligotrophic lake and is bottom-up
regulated by nutrients (at least for now). 3.
Salmon population crashed. 4. Eagles stopped
coming to McDonald Creek 1981 639 eagles 1989
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Mean shrimp, salmon,and eagle abundance in
Flathead Lake and McDonald Creek.
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Bald eagles and Kokanee spawners in McDonald
Creek, 1979-1989.
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What happened as a result of opossum
introduction? 1. Zooplankton population
decreased 2. No increase in phytoplankton
production. Flathead Lake is an
ultra-oligotrophic lake and is bottom-up
regulated by nutrients (at least for now). 3.
Salmon population crashed. 4. Eagles stopped
coming to McDonald Creek 5. Bears and tourists
stopped coming also.
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Why were the results of introduction of shrimp to
Flathead Lake so different than what happened in
Kootenay Lake? Kokanee salmon normally feed near
the surface -- top 30 m or so. Opossum shrimp
exhibit vertical migration to avoid predation
from fish.
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Vertical distribution of opossum shrimp in
Flathead Lake, August 1988.
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In Kootenay Lake there are upwelling currents
that bring deep water up into shallow areas. In
Flathead Lake, the shrimp are able to completely
avoid predation from the salmon. Instead, they
compete with the salmon for food.
Now Kokanee salmon are absent from the
lake. Opossum shrimp levels fluctuate. Lake
trout and lake whitefish are the dominant
fish. Many fewer fishermen lots of
development
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