George Morgan

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Lake TemagamiFall Walleye Index Netting Project
2001

• George Morgan
• Extension Biologist
• Cooperative Freshwater Ecology Unit

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What is Index Netting?

• Index netting is a standardized, rapid assessment
  technique or method that is designed to determine
  relative abundance and provide other biological
  measures or indicators of a fish populations
  status

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QA What method should I use to assess my
walleye population?

• Are you interested in
• Adult and juvenile walleye
• Is lethal sampling acceptable?
• Yes
• No
• Then use
• Fall Walleye Index Netting (FWIN)
• Early Summer Trap Netting (ESTN)

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What is Fall Walleye Index Netting?

• Gillnetting procedure in the fall
• Net is 8 panels each 7.6m by 1.8m
• 25, 38, 51, 64, 76, 102, 127 152mm mesh
• Temperature 15?10oC
• Random net locations
• 2 depth strata
• 2-5m 5-15m
• Kills fish!

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What can you measure with FWIN?

• Species and number caught
• Fork and total length, girth
• Wet, dressed, and filet weight
• Bony structures for age interpretation
• Determine sex and maturity
• Stomach contents
• Gonad weight
• Organ weight (e.g., liver)
• Visceral fat weight
• Contaminant and genetic samples

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QA What method should I use to assess my
walleye population?

• Are you interested in
• Adult walleye (gt300mm total length)
• Is lethal sampling acceptable?
• Yes
• No
• Then use
• Fall Walleye Index Netting (FWIN)
• Early Summer Trap Netting (ESTN)

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What is Early Summer Trap Netting?

• Trapnetting procedure in the early summer
• NSCIN net
• 1.8m trapnet with 45.7m leader
• Temperature 12?18oC
• Random net locations
• Specific site selection criteria
• Live release of fish!

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What can you measure with ESTN?

• Species and number caught
• Fork and total length, girth
• Wet, dressed, and filet weight?
• Bony structures (spines)
• Determine sex and maturity
• Stomach contents
• Gonad weight
• Organ weight (e.g., liver)
• Visceral fat weight
• Contaminant and genetic samples

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Lake Temagami isNot your Typical Walleye Lake

• Lake Temagami
• Area 20971.7ha
• Max. depth 110m
• Mean depth 18.2m
• Secchi 10.7m
• GDD 1538

• Ontario Walleye Lakes
• Area 102 to 759ha
• Max. depth 8.2 to 23.6m
• Mean depth 2.7 to 4.3m
• Secchi 2.0 to 3.7m
• GDD 1275 to 1500

So Lake Temagami is a large, deep, clear, cool
lake (should be more favourable for coldwater
species like lake trout).
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Lake Temagami FWIN 2001

• Concentrated sampling effort in The Hub
  (recommended sampling area by Chuck McCrudden)
• Crew set and lifted 6 nets per day from September
  26 to 30th
• Total of 24 sets (22 useful sets 2 tampered)

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Lake Temagami FWIN 2001

• WHAT DID WE CATCH?
• 1 Lake trout
• 49 Lake whitefish
• 63 Lake herring
• 8 Northern pike
• 68 White sucker
• 1 Lake chub

• 1 Burbot (Ling)
• 105 Rock bass
• 1 Pumpkinseed
• 38 Smallmouth bass
• 14 Yellow perch
• 127 WALLEYE

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Making a Diagnosis
How is the health of the patient today?

• Compare observed FWIN walleye abundance (number
  per net) to other Ontario lakes
• Abundance compared to provincial and northeast
  region benchmarks

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Walleye Relative Abundance
Lake Temagami abundance as expected based on
climate and productivity.
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Making a Diagnosis (Forecast)

• Compare biological parameters to regional
  benchmarks
• Compare biological parameters to regional
  regression models

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Making a Diagnosis (Forecast)

• Compare biological parameters to regional
  benchmarks
• Compare biological parameters to regional
  regression models

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What information can I get from a FWIN survey?

• Relative abundance
• Size distribution
• Age distribution mortality
• Growth condition
• Sex ratio maturity
• Reproductive characteristics
• Relative stock density

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Lake Temagami WalleyeSize Distribution
Lake Temagami average size 362mm (14.2in).

Smallest fish 132mm (5.2in). Largest fish 760mm
(29.9in).
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Lake Temagami WalleyeCorrected Size
Distribution
Lake Temagami slot will protect 5.7 of the
population.
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Lake Temagami WalleyeAge Distribution (by sex)
Average age 2.5 years. Oldest fish 14 years.
Balanced sex ratio
(49 males 51 females).
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Lake Temagami WalleyeCorrected Age Distribution
Population supported by 3 strong year-class (1999
to 2001). Annual adult mortality is 29
after age 5 (too high).
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Lake Temagami Walleye Growth
Lake Temagami male and female size is much higher
than regional average after age 1.
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Lake Temagami Walleye Condition
Lake Temagami male and female condition is higher
than regional average.
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Lake Temagami Walleye Maturity by Size
Males 50 mature at 373mm (14.7in). Females 50
mature 448mm (17.6in) and 90 mature at 471mm
(18.5in).
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Lake Temagami Walleye Maturity by Age
Males 50 mature at 2.5yrs. Females 50 mature at
3.6yrs.
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Lake Temagami WalleyeEgg Production
Lake Temagami egg production is much lower than
regional average.
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Lake Temagami Walleye Fecundity-by-Size
Lake Temagami fecundity is much lower than
regional trendline.
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Making a Diagnosis (Forecast)

• Compare biological parameters to regional
  benchmarks
• Compare biological parameters to regional
  regression models

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Important life history questions
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NE Female Walleye Life History
Relationships
Environment (Growing Degree Days, Secchi )
Early growth (h mm/yr) h 60.055 12.253
Secchi , R2 0.26 Relative
Condition Relative Conditionf 0.762
0.0002 GDD , R2 0.24
Length at maturation (mm) Lmf 369.116 0.782
h , R2 0.17
Gonadosomatic index () GSIf 1.725 0.024 h
, R2 0.26
Visceral fat index () VFIf -10.407 12.291
Conditionf , R2 0.42
Potential population increase (r') r' 0.020 h
0.002 GDD - 1.477, R2 0.67
Asymptotic length (mm) L? 526.636 - 4.922 A
0.840 Lmf , R2 0.60
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Lake Temagami Female Walleye
Lake Temagami Environmental Conditions (Growing
Degree Days 1538, Secchi 10.7m?)
Early growth (h mm/yr) Predicted h 191mm/yr
Observed h 113mm/yr Unexploited population h
51mm/yr Relative Condition Predicted Relative
Conditionf 1.07 Observed Relative Conditionf
1.06
Length at maturation (mm) Predicted Lmf 457mm
Observed Lmf 448mm
Gonadosomatic index () Predicted GSIf 4.43
NO DATA COLLECTED
Visceral fat index () Predicted VFIf 2.62 NO
DATA COLLECTED
Potential population increase (r') Predicted r'
3.85 Observed r' 2.83 to 3.03
Asymptotic length (mm) Predicted L? 775mm
Observed L? 792mm
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Lake Temagami Walleye Status

• This lake supports a stressed walleye population.
  The population is dominated by young, immature,
  fast growing year-classes. Mortality is high
  enough to lower the number of adult walleye
  present in this population and few fish reach old
  age.

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Any Questions or Comments?