status of lake trout in the main basin of lake huron: a summary of (scaa) models and projections...
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Status of Lake Trout in the Main Basin of Lake Huron: A
Summary of (SCAA) Models and Projections
Aaron Woldt--MDNR Alpena
Background• Lake Huron lake trout stocks crashed due to
overfishing and mortality due to sea lamprey in the 1940’s
• Rehabilitation efforts started in the 1970’s and consisted primarily of:
» supplemental stocking» lamprey control» fishery regulation
• Lake trout stocks are monitored annually by MDNR, CORA, USGS BRD, OMNR, and USFWS
We developed 2 types of models
1) SCAA model--uses user supplied inputs and iteratively solves for population parameters like M, F, Z, abundance, SSB….
2) Projection model--uses last year’s output from SCAA model to predict population parameters into the future (2020 in our case). Also allows user to alter projection parameters (i.e. effort).
We developed both model types for each modeled area
Inputs to SCAA model
• Stocking (w/ movement matrix)
• Commercial fishery effort and yield (state licensed, tribal, and Canadian) from LMGN, SMGN, and trap nets
• Recreational fishery effort and harvest
• Commercial and recreational harvest age compositions
• Mean weight of lake trout harvested by each gear (LMGN, SMGN, trap net)
Inputs to SCAA model (cont.)
• Estimate of under-reporting or discards• Survey catch, CPE, and age compositions• Estimate of natural mortality• Estimate of sea lamprey mortality rates at age by year• Estimate of trap net by-catch mortality• Estimate of lake trout weight at age• Estimate of lake trout maturity at age • Estimate of fecundity
Areas modeled using SCAA
NorthernNorth-centralSouthernNot modeled
Model Key
MH-1 and 4-1
MH-2, 4-2, 4-3, and 4-7
MH-3, MH-4, MH-5,4-4, and 4-5
Credit:GLFC
Is this natural?
Sources of Mortality
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Historic lake trout spawning reefs
0.00
0.20
0.40
0.60
0.80
1.00
1.20
1.40
1.60
1977 1979 1981 1983 1985 1987 1989 1991 1993 1995 1997
Year
Inst
anta
neou
s M
orta
lity
Rat
e (Z
) RecreationalCommercialLampreyNatural
Average instantaneous mortality rates for ages 3-13 lake trout in N. L. Huron
0
50,000
100,000
150,000
200,000
250,000
300,000
350,000
400,000
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
Age
Nu
mb
er
of L
ake
Tro
ut
1994-98 average lake trout population age structure in N. L. Huron
1,818 523 163 1445 5 1 07,359
0
100
200
300
400
500
600
700
1977 1979 1981 1983 1985 1987 1989 1991 1993 1995 1997
Year
Biom
ass
X 1,
000
kg
Total Biomass
SSB
SCAA model estimates of lake trout biomass and SSB in N. L. Huron
N. L. Huron Projection Scenarios
0.000
0.050
0.100
0.150
0.200
0.250
Targe
t A =
0.4
5
Curre
nt (1
998)
Lam
prey
Only
Total F
-50%
Total F
-63%
Comm
-50%
Comm
-60%
Comm
-70%
Comm
-50%
+ 2
4"
Comm
-60%
+ 2
4"
Comm
-70%
+ 2
4"
SS
BR
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
1984 1986 1988 1990 1992 1994 1996 1998Year
Inst
anta
neou
s M
orta
lity R
ate
(Z)
RecreationalCommercialLampreyNatural
Average instantaneous mortality rates for ages 3-13 lake trout in N.C. L. Huron
0
50,000
100,000
150,000
200,000
250,000
300,000
350,000
400,000
450,000
500,000
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
Age
Nu
mb
er
La
ke
Tro
ut
1994-98 average lake trout population age structure in N.C. L. Huron
4,6022,161
1,330 734 305 16521,648
11,2608,195
0100200300400500600700800900
1984 1985 1986 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998
Year
Biom
ass
X 1,
000
kg
Total Biomass
SSB
SCAA model estimates of lake trout biomass and SSB in N.C. L. Huron
CPE of YOY lake trout at North Point Thunder Bay
0.0
0.5
1.0
1.5
2.0
2.5
3.0
Year
CPE
(YO
Y/to
w)
Combination of habitat and adult spawners, albeit a low level of spawners
N.C. L. Huron Projection Scenarios
0.000.100.200.300.400.500.600.700.800.901.00
SS
BR
0.000.050.100.150.200.250.300.350.400.450.50
1984 1986 1988 1990 1992 1994 1996 1998Year
Inst
anta
neou
s M
orta
lity
Rat
e (Z
)
RecreationalCommercialLampreyNatural
Average instantaneous mortality rates for ages 3-13 lake trout in S. L. Huron
0
50,000
100,000
150,000
200,000
250,000
300,000
350,000
400,000
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
Age
Nu
mb
er
La
ke
Tro
ut
1994-98 average lake trout population age structure in S. L. Huron
9,8966,331
4,322
2,5872,241 617
112,999
56,559
24,742 1,466927
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Historic lake trout spawning reefs
Potential for natural production in MH-3,4,5??Relatively high numbers ofspawners (5X that of MH-2)but little nearshore habitat.
We currently do not trawlfor juveniles in MH-3,4,5
0
500
1,000
1,500
2,000
2,500
3,000
3,500
1984 1985 1986 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998
Year
Biom
ass
X 1,
000
kg
Total Biomass
SSB
SCAA model estimates of lake trout biomass and SSB in S. L. Huron
Estimated lake trout sport catch, Michigan waters of Lake Huron
0
10,000
20,000
30,000
40,000
50,000
60,000
70,000
80,000
1986 1988 1990 1992 1994 1996 1998
Year
Num
ber o
f fis
h
MH-6MH-5MH-4MH-3MH-2MH-1
**note 1999 catch does not include charter boats
0.0
0.2
0.4
0.6
0.8
1.0
1.2
Targ
et A
= 0
.4
Curre
nt (1
998)
Lam
prey
Onl
y
Tota
l F -5
0%
Comm
-50%
Sport
- 50%
24" R
ec
Comm
-50%
& 2
4" R
ec
1.5
X Tot
al F &
24"
Rec
SS
BR
S. L. Huron Projection Scenarios
Southhampton
Goderich, ON, CA
Alpena, MI, USA
Tawas
Harrisvi NFL or NHL??Bud or LaBatt’s??So many choices.
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Gillnet returns of CWT LT from Six Fathom Bank
Summary1) The management strategy now in place in the main
basin of Lake Huron may allow for the rehabilitation of lake trout stocks by 2020.
2) Control of sea lamprey and fishing mortality is necessary for rehabilitation to progress.
3) Cooperative management between USA, 1836 tribes, and Canada is needed to control lake trout mortality in the main basin of Lake Huron.
Summary (cont.)
4) The modeling subcommittee of the Technical Fisheries Committee will update the SCAA models yearly to set TAC’s and monitor progress towards rehabilitation.
We are updating models with data through the year 2000 right now. Preliminary TAC’s are due next week.
Thank God we all made it out in time. ‘Course, now we’re equally screwed.
Thank God we all made it out in time. ‘Course, now we’re equally screwed.
Southhampton
Goderich, ON, CA
Alpena, MI, USA
Tawas
Harrisvi ANY QUESTIONS?