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Some basic tools for using population ecology as a management tool –
A Primer
• GROWTH
• RECRUITMENT
• MORTALITY
• COMPENSATION
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Lake Pend Oreille
An On-the-Ground Application of Population Ecology
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LPO Fishery - Desired Outcomes
• Ross Hall photos
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Adult Kokanee Abundance in Lake Pend Oreille
0
1
2
3
4
5
6
7
852 56 60 64 68 72 76 80 84 88 92 96
2000
Year
Kok
anee
abu
ndan
ce
Drawdowns to 2051 ft became routine beginning in 1966
Shrimp established in 1975
Albeni Falls Dam Built
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KOKANEE SURVIVALKOKANEE SURVIVAL
• Declined in 2007; low for all agesDeclined in 2007; low for all ages
• Survival less than 50% is a concernSurvival less than 50% is a concern
• Predation limiting survival to spawningPredation limiting survival to spawning
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Indices of LT Abundance, Lake Pend Oreille
0
2000
4000
6000
8000
10000
12000
14000
16000
18000
20000
1953
1985
1992
1994
1996
1998
2000
2002
2004
2006
Harvest Est.
Pop. Estimate
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LPO Kokanee
• Primarily lake spawners, some tributary spawners, hatchery supplementation
• Longevity – 4 to 5 years (die after spawning)• Relatively low fecundity, but high plasticity
(compensatory ability)• Planktivores• Key prey item for BLT, RBT, LT as well as avian and
terrestrial predators
• Principle threats:– Predation– Habitat impacts
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LPO Lake trout
• Lake spawners (fall)• Longevity – 30+ years, mature at 7 years• Highly piscivorous, but can survive on Mysis• Slow growth• Relatively low fecundity
• Principle threat:– Directed harvest
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Lake TroutFishery Management
• Lake trout are late maturing and long lived, so are vulnerable to over-fishing.
• The largest lake trout populations were over-fished in the Great Lakes before sea lamprey became a problem.
• Most lake trout populations in Ontario inland lakes are considered over-fished.
• Lake Pend Oreille is a field test of over-fishing of lake trout!
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Lake TroutSize Structure
0%
5%
10%
15%
20 40 60 80 100
Length (cm)
Pe
rce
nt
Gillnets
Trapnets
Angling
IDFG 2007
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Lake TroutGrowth
0
20
40
60
80
100
0 5 10 15 20 25
Age (years)
Le
ng
th (
cm)
Superior, MI
Michigan, WI
Pend Oreille, ID
McKee et al. 2004Burnham-Curtis and Bronte 1996
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Lake TroutMaturity
0%
20%
40%
60%
80%
100%
450 500 550 600 650 700 750 800
Length Class (mm)
Mat
urity
(%
)
Males(6.5 years)
Females(7.3 years)
IDFG 2007
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Lake TroutFuture Prognosis?
0
10,000
20,000
30,000
40,000
50,000
60,000
70,000
80,000
90,000
100,000
1999 2001 2003 2005 2007 2009 2011 2013 2015
Year
Ab
un
da
nce
Observed Predicted
0
10,000
20,000
30,000
40,000
50,000
60,000
70,000
80,000
90,000
100,000
1999 2001 2003 2005 2007 2009 2011 2013 2015
Year
Ab
un
da
nce
Observed Predicted
This?
Or,this?
Which is better forLake Pend Oreille?
IDFG 2007
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Kokanee Biomass,Production and Yield
This
Or This 0
50
100
150
200
250
300
350
400
2000 2020 2040 2060 2080 2100 2120 2140 2160 2180 2200
Year
Kok
anee
(mt)
Biomass
Production
Yield
0
50
100
150
200
250
300
350
400
2000 2020 2040 2060 2080 2100 2120 2140 2160 2180 2200
Year
Ko
ka
ne
e (
mt)
Biomass
Production
Yield
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Lake TroutFishery Management
0
500
1,000
1,500
2,000
2,500
3,000
3,500
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
Month
Num
ber
Kill
ed
0
5,000
10,000
15,000
20,000
25,000
30,000
35,000
40,000
Abundance
Angling
Trap Nets
Gill Nets
Natural
Abundance
IDFG 2007
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Lake TroutMortality
• Natural (LPO2006 = 15.1% estimate):– Average = 18% (much higher if lampreys).– Range = 10–36% (much higher if lampreys).
• Fishing (LPO2006 > 44.5%; 0.58kg/ha):– Highest = 45% (Superior prior to lamprey).– Populations decline if harvest > 0.50 kg/ha.
• Total (LPO2006 > 59.6%):– Populations are sustainable if A < 50%.– Most populations decline if A > 50%!
Healey 1978
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Can it work?
• Lake trout exploitation (angling & commercial nets) ~50%– Exploitation rates of ~ 40% collapsed Great
Lakes fisheries• Rainbow trout
exploitation still
low• Predation still
too high
1879 1889 1899 1909 1919 1929 1939 1949 1959
Year
0
1
2
3
4
5K
ilogr
ams (
mill
ions
)
Lake Michigan lake trout
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Lake TroutLake TroutDistributionDistribution
Great Slave Lake(27,195 km2)
(625 m)
Great Bear Lake(31,153 km2)
(452 m)
Lake Superior(82,414 km2)
(405 m)
Lake Michigan(58,016 km2)
(285 m)
Lake Huron(59,596 km2)
(220 m)
Lake Erie(25,745 km2)
(64 m)
Lake Ontario(19,529 km2)
(237 m)
Lake Pend Oreille(383 km2)(351 m)
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Probability of Kokanee CollapseWith Different Mortality Rates for RBT and LT
0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
-30% -20% -10% 0% 10% 20% 30% 40% 50%
Change in Mortality
Lik
elih
oo
d o
f Ko
kan
ee
Co
llap
se
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Bottom Line for Success on LPO:• We need to reduce predation on kokanee by
50 tons annually to begin kokanee recovery • RBT and LT are the two primary predators• Current needs – harvest LT and RBT to
reduce predation and slow growth of LT population
• LT will need to be managed at a suppressed level for the long term
• The public will need to support programs
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Some Take-Away Points For F&W
Population Management: • If R>M populations grow, and vice versa• More fecund animal populations apt to grow more
rapidly in good, unoccupied habitat• Many species “compensate” at low densities by
increasing growth rates, lowering age of reproduction & increasing fecundity
• Late maturing, lower fecundity populations more susceptible to mortality agents
• “Predator pits” more likely to occur when predator species has abundant supply of alternative prey
• Habitat conditions affect R & M, but so also can external forces (Exploitation, Predation, Competition, Disease, etc)
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Information and slides for this presentation were contributed by Melo Maiolie, Mike Hansen and Ned Horner.