Stock Characteristics of Lake Whitefish in Lake Michigan
Matthew Belnap Daniel Isermann
Brian Sloss
Justin VanDeHey
Keith Turnquist
Lake Whitefish in Lake Michigan
• Native
• Benthivorous fish • Important for energy transfer in Great Lakes
• Socioeconomically important to Great Lakes Basin
• Highly mobile
• Natal homing
Commercial Fishery
• Most lucrative commercial fishery on Lake Michigan
• Dockside value of $2.5‐
$5.5 million
• Growing roe market (caviar)
• Current value $160 per pound
Historical Harvest
25
Relative Harvest
20
15
10
5
0
1865
1885
1905
1925 1945
Year
** Data compiled from Great Lakes Fishery Commission database
1965 1985 2005
Management
03
• Inter‐jurisdictional fishery
01
05
• WDNR
• MDNR • CORA • Quotas based on statistical catch‐at‐age models • 13 management zones
04
02
WI‐2
07
WI‐3
08
09
06
Management
• Issues
•
•
•
•
Multiple agencies
Length of season
Recreational fishery
Superficial boundaries
• Ebener (1985) tagging study • Potential for a mixed‐
stock fishery
Stock Concept
• Stock is the basic unit of a fishery or a “management unit”
• Component of a fishery susceptible to harvest
• Useful when:
• Describing population dynamics
• Setting quotas or harvest regulations
• Maintaining sustainability of a fishery
Genetic Stock Concept
• Larkin (1972): “…a group of organisms, sharing a gene pool, that is sufficiently discrete and nominally identifiable that warrants management as such.” Genetic Stock Concept
• To conserve genetic diversity through time
•
•
•
•
Local adaptations
Adaptability
Resilience
Sustainability
LWF Task Group
• 2001 LWF task recognized knowledge was insufficient to discriminate or manage LWF on a stock specific basis
• Recommended combining genetics and biological characteristics to rectify this issue
Recent Research
• 6 genetically distinct stocks
• Based on variation at 11 microsatellite loci
• Next step mixed‐stock analysis
NOR
BBN
GB
ER
SOU
Recent Research
• Mixed‐stock analysis
• Closest stock consistently < 60% of harvest
• Composition of geographical stocks dynamic throughout commercial season and year to year
Recent Research
• Mixed‐stock analysis
• Closest stock consistently < 60% of harvest
• Composition of geographical stocks dynamic throughout commercial season and year to year
Recent Research
• Mixed‐stock analysis
• Closest stock consistently < 60% of harvest
• Composition of geographical stocks dynamic throughout commercial season and year to year
36%
Recent Research
• Mixed‐stock analysis
• Closest stock consistently < 60% of harvest
• Composition of geographical stocks dynamic throughout commercial season and year to year
36%
37%
Recent Research
36%
0%
• Mixed‐stock analysis
• Closest stock consistently < 60% of harvest
• Composition of geographical stocks dynamic throughout commercial season and year to year
BBN
37%
Recent Research
36%
0%
• Mixed‐stock analysis
27%
• Closest stock consistently < 60% of harvest
• Composition of geographical stocks dynamic throughout commercial season and year to year
BBN
GB
37%
Objectives
1. Determine if the accuracy of stock identification based on capture location varies by sampling period
2. Determine if biological differences exist among stocks
Sample sites
Wisconsin
• WI‐2
03
01
04
02
05
WI‐2
07
WI‐3
08
09
06
Michigan
• WFM‐02
• WFM‐03
• WFM‐05
• WFM‐07
• WFM‐08
Methods
1,200 lake whitefish total
October 1‐15 (early)
October 16‐31 (late)
Target of 100 fish per genetic stock per year
• 1:1 sex ratio
•
•
•
•
Data collection
•
•
•
•
•
•
Weight
Total length
Sagittal otoliths
Pelvic fin clip Gonad mass
Gonad condition
Methods
Stock Assignment
• 12 microsatellite loci
• ONCOR software
• Individual assignment to stock
Microsatellite?
•
•
•
•
Non coding region of DNA
Repeating patterns of base pairs
No known biological function Surrogates for genetic diversity
Methods
Biological Characteristics
• Age structure
• Back‐calculated mean total lengths‐at‐age
• Length frequency
• Weight‐length relationships
• Growth
• Fecundity
Methods
Age Structure
• Age estimation using otoliths
• Image Pro® for otolith
imaging
Male LWF
TL= 486 mm
10/4/2012 Naubinway, MI
What is an Otolith?
Male LWF
TL = 486
Naubinway, MI
Methods
Fecundity
• Gravimetric method
• Weigh and enumerate multiple subsamples of 50‐100 eggs
Preliminary Results
Objectives
1. Determine if the accuracy of stock identification based on capture location varies by sampling period
2. Determine if biological differences exist among stocks
Results
Stock Assignment
100%
% Likelihood
80%
60%
NOE
N=100
40%
SOU
20%
0%
Individual
SOU
NOE
Results
Stock Assignment
100%
% Likelihood
80%
NOE
60%
40%
SOU
SOU
20%
0%
Individual
SOU
NOE
Results
Stock Assignment
100%
% Likelihood
80%
60%
NOR
NOE
N=50
40%
20%
0%
Individual
NOR
NOE
Results
Stock Assignment
100%
% Likelihood
80%
NOR
NOE
60%
NOR
40%
20%
0%
Individual
NOR
NOE
Results
Stock Assignment
100%
% Likelihood
80%
NOR
NOE
60%
NOE
NOR
40%
20%
0%
Individual
NOR
NOE
Results
Stock Assignment
100%
% Likelihood
80%
NOR
NOE
60%
NOR
40%
NOE
?
20%
0%
Individual
NOR
NOE
Objectives
1. Determine if the accuracy of stock identification based on capture location varies by sampling period
2. Determine if biological differences exist among stocks
Results
Fecundity All Stocks
70000
60000
Fecundity
50000
40000
30000
Slopes
F = 0.18
df = 9, 183
P = 0.95
20000
10000
0
0
500
1000
1500
Weight (g)
2000
2500
3000
Results
Expected Fecundity for a 1,325 g Female LWF
Stock
Expected Fecundity
Southern
24,241
Northeast
BigBaydeNoc
GreenBay
Northern
25,043
22,414
21,597
21,813
Results
Expected Fecundity for a 1,325 g Female LWF
Stock
Expected Fecundity
Southern
24,241
Northeast
BigBaydeNoc
GreenBay
Northern
25,043
22,414
21,597
21,813
• The greatest difference among expected fecundities was 16%.
Results Female Weight‐Length Relationships
4.00
3.50
Log10(W)
3.00
2.50
Slopes
F = 2.11
df = 8, 186
P = 0.10
2.00
1.50
1.00
0.50
0.00
2.55
2.60
2.65
2.70
2.75
Log10(TL)
2.80
2.85
2.90
Results Expected Weights for a 525 mm Female LWF
Stock
Expected Weight (g)
GreenBay
1,222
Northern
1,285
BigBaydeNoc
1,266
Southern
1,375
Results Expected Weights for a 525 mm Female LWF
Stock
Expected Weight (g)
GreenBay
1,222
Northern
1,285
BigBaydeNoc
1,266
Southern
1,375
• The greatest difference among expected weights was 12.5%
Results
Age Structure
Stock
Mean Age
SD
Southern
8.90
0.82
Northeast
7.05
0.67
Results Age Structure
Frequency
30
25
Southern
20
15
Northeast
10
5
0
5
6
7
8
Age
9
10
11
12
Summary
• Stock assignment based on capture location is better at some sites than others
• No significant difference in stock‐specific fecundity
• No significant difference in female W‐L relationships
• Age structure shows potential differences
Acknowledgments
• MDNR
• WDNR
Scott Hansen
Ken Royseck
R/V Coregonus Crew
• Marty Holtgren (LRBOI)
Dave Caroffino
Randy Claramunt
• Mark Ebener (CORA)
• Erik Olsen (GTBNR)
All Commercial Fishermen
Questions