George MorganGeorge Morgan

Extension BiologistExtension Biologist

Cooperative Freshwater Ecology UnitCooperative Freshwater Ecology Unit

Lake TemagamiLake TemagamiFall Walleye Index Netting Project 2001Fall Walleye Index Netting Project 2001

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

What is Index Netting?What is Index Netting?

Q&A: What method should I use to Q&A: What method should I use to assess my walleye population?assess my walleye population?

Are you interested in…Are you interested in… Adult and juvenile walleyeAdult and juvenile walleye

Is lethal sampling acceptable?Is lethal sampling acceptable? YesYes NoNo

Then use…Then use… Fall Walleye Index Netting (FWIN)Fall Walleye Index Netting (FWIN) Early Summer Trap Netting (ESTN)Early Summer Trap Netting (ESTN)

What is Fall Walleye Index What is Fall Walleye Index Netting?Netting?

Gillnetting procedure in the fallGillnetting procedure in the fall Net is 8 panels each 7.6m by 1.8m:Net is 8 panels each 7.6m by 1.8m:

– 25, 38, 51, 64, 76, 102, 127 & 152mm mesh25, 38, 51, 64, 76, 102, 127 & 152mm mesh

Temperature 15Temperature 151010ooCC Random net locationsRandom net locations 2 depth strata:2 depth strata:

– 2-5m & 5-15m2-5m & 5-15m

Kills fish!Kills fish!

What can you measure with What can you measure with FWIN?FWIN?

Species and number caughtSpecies and number caught Fork and total length, girthFork and total length, girth Wet, dressed, and filet weightWet, dressed, and filet weight Bony structures for age interpretationBony structures for age interpretation Determine sex and maturityDetermine sex and maturity Stomach contentsStomach contents Gonad weightGonad weight Organ weight (e.g., liver)Organ weight (e.g., liver) Visceral fat weightVisceral fat weight Contaminant and genetic samplesContaminant and genetic samples

Q&A: What method should I use to Q&A: What method should I use to assess my walleye population?assess my walleye population?

Are you interested in…Are you interested in… Adult walleye (>300mm total length)Adult walleye (>300mm total length)

Is lethal sampling acceptable?Is lethal sampling acceptable? YesYes NoNo

Then use…Then use… Fall Walleye Index Netting (FWIN)Fall Walleye Index Netting (FWIN) Early Summer Trap Netting (ESTN)Early Summer Trap Netting (ESTN)

What is Early Summer Trap What is Early Summer Trap Netting?Netting? Trapnetting procedure in the early Trapnetting procedure in the early

summersummer NSCIN net:NSCIN net:

– 1.8m trapnet with 45.7m leader1.8m trapnet with 45.7m leader

Temperature 12Temperature 121818ooCC Random net locationsRandom net locations Specific site selection criteriaSpecific site selection criteria Live release of fish!Live release of fish!

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

What can you measure with What can you measure with ESTN?ESTN?

Lake Temagami isLake Temagami isNot your Typical Walleye LakeNot your Typical Walleye Lake

Lake TemagamiLake Temagami Area = 20971.7haArea = 20971.7ha Max. depth = 110mMax. depth = 110m Mean depth = 18.2mMean depth = 18.2m Secchi = 10.7mSecchi = 10.7m GDD = 1538GDD = 1538

Ontario Walleye LakesOntario Walleye Lakes Area 102 to 759haArea 102 to 759ha Max. depth 8.2 to 23.6mMax. depth 8.2 to 23.6m Mean depth 2.7 to 4.3mMean depth 2.7 to 4.3m Secchi 2.0 to 3.7mSecchi 2.0 to 3.7m GDD 1275 to 1500GDD 1275 to 1500

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

Lake Temagami FWIN 2001Lake Temagami FWIN 2001

Concentrated sampling Concentrated sampling effort in “The Hub” effort in “The Hub” (recommended (recommended sampling area by Chuck sampling area by Chuck McCrudden)McCrudden)

Crew set and lifted 6 Crew set and lifted 6 nets per day from nets per day from September 26 to 30thSeptember 26 to 30th

Total of 24 sets (22 Total of 24 sets (22 useful sets; 2 tampered)useful sets; 2 tampered)

Lake Temagami FWIN 2001Lake Temagami FWIN 2001

WHAT DID WE CATCH?WHAT DID WE CATCH? 1 Lake trout1 Lake trout 49 Lake whitefish49 Lake whitefish 63 Lake herring63 Lake herring 8 Northern pike8 Northern pike 68 White sucker68 White sucker 1 Lake chub1 Lake chub

1 Burbot (Ling)1 Burbot (Ling) 105 Rock bass105 Rock bass 1 Pumpkinseed1 Pumpkinseed 38 Smallmouth bass38 Smallmouth bass 14 Yellow perch14 Yellow perch 127 WALLEYE127 WALLEYE

Making a DiagnosisMaking a Diagnosis

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

benchmarksbenchmarks

How is the healthHow is the healthof the “patient” today?of the “patient” today?

Walleye Relative AbundanceWalleye Relative Abundance

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45

Temagami NE Benchmark Provincial Benchmark

Num

ber

of w

alle

ye p

er n

et

High

Average

Low

Lake Temagami abundance as expected based on climate and productivity.

Making a Diagnosis (Forecast)Making a Diagnosis (Forecast)

Compare biological parameters to regional Compare biological parameters to regional benchmarksbenchmarks

Compare biological parameters to regional Compare biological parameters to regional regression modelsregression models

Making a Diagnosis (Forecast)Making a Diagnosis (Forecast)

Compare biological parameters to regional Compare biological parameters to regional benchmarksbenchmarks

Compare biological parameters to regional Compare biological parameters to regional regression modelsregression models

What information can I get from a What information can I get from a FWIN survey?FWIN survey?

Relative abundanceRelative abundance Size distributionSize distribution Age distribution & mortalityAge distribution & mortality Growth & conditionGrowth & condition Sex ratio & maturitySex ratio & maturity Reproductive characteristicsReproductive characteristics Relative stock densityRelative stock density

ProtectedSlot

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140 180 220 260 300 340 380 420 460 500 540 580 620 660 700 740 780

Total Length (mm)

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atch

Lake Temagami WalleyeLake Temagami WalleyeSize DistributionSize Distribution

Lake Temagami average size 362mm (14.2in). Smallest fish 132mm (5.2in). Largest fish 760mm (29.9in).

ProtectedSlot

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Total Length (mm)

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atch

Corrected

Observed

Lake Temagami WalleyeLake Temagami Walleye“Corrected” “Corrected” Size DistributionSize Distribution

Lake Temagami slot will protect 5.7% of the population.

Lake Temagami WalleyeLake Temagami WalleyeAge Distribution (by sex)Age Distribution (by sex)

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Age (years)

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alle

ye

MalesFemalesUnknowns

Average age 2.5 years. Oldest fish 14 years. Balanced sex ratio (49% males: 51% females).

Lake Temagami WalleyeLake Temagami Walleye“Corrected” Age Distribution“Corrected” Age Distribution

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Age (years)

% o

f P

opul

atio

n

Corrected

Observed

Population supported by 3 strong year-class (1999 to 2001). Annual adult mortality is 29% after age 5 (too high).

ProtectedSlot

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th (

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)

NE male benchmark

NE female benchmark

Temagami males

Temagami females

Lake Temagami Walleye Lake Temagami Walleye GrowthGrowth

Lake Temagami male and female size is much higher than regional average after age 1.

Lake Temagami Walleye Lake Temagami Walleye ConditionCondition

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Total Length (mm)

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ght (

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NE male benchmark

NE female benchmark

Temagami malesTemagami females

Lake Temagami male and female condition is higher than regional average.

ProtectedSlot

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Temagami males

Temagami females

Lake Temagami Walleye Lake Temagami Walleye Maturity Maturity by Sizeby Size

Males 50% mature at 373mm (14.7in). Females 50% mature 448mm (17.6in) and 90% mature at 471mm (18.5in).

Lake Temagami Walleye Lake Temagami Walleye Maturity Maturity by Ageby Age

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cent

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ure

Temagami males

Temagami females

Males 50% mature at 2.5yrs. Females 50% mature at 3.6yrs.

Lake Temagami WalleyeLake Temagami WalleyeEgg ProductionEgg Production

35000

40000

45000

50000

55000

60000

Temagami NE benchmark

Egg

s pe

r ki

logr

am

Lake Temagami egg production is much lower than regional average.

Lake Temagami Walleye Lake Temagami Walleye Fecundity-by-SizeFecundity-by-Size

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ggs

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NE benchmark

Temagami trendline

Lake Temagami fecundity is much lower than regional trendline.

Making a Diagnosis (Forecast)Making a Diagnosis (Forecast)

Compare biological parameters to regional Compare biological parameters to regional benchmarksbenchmarks

Compare biological parameters to regional Compare biological parameters to regional regression modelsregression models

Important life history questionsImportant life history questions

Tot

al L

engt

h (m

m)

Age at time t (yr)

L

Tmature

slop

e =

h

Lm

How fast do walleye grow?How fast do walleye grow? Pre-maturation growth is linearPre-maturation growth is linear Growth after maturity follows von Growth after maturity follows von

Bertalannfy growth formulaBertalannfy growth formula

When do walleye mature?When do walleye mature? What is their potential rate of What is their potential rate of

population increase?population increase?rr’’ = ( = (lnln fecundity @ L fecundity @ Lmm)/T)/Tmaturemature

Lt = L (1-e -K(t-t0 ))

Environment(Growing Degree Days, Secchi )

Early growth (h = mm/yr)h = 60.055 + 12.253 Secchi , R2 = 0.26

Relative ConditionRelative Conditionf = 0.762 + 0.0002 GDD , R2 = 0.24

Length at maturation (mm)Lmf = 369.116 + 0.782 h , R2 = 0.17

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 , R

2 = 0.60

Gonadosomatic index (%)GSIf = 1.725 + 0.024 h , R2 = 0.26

Visceral fat index (%)VFIf = -10.407 + 12.291 Conditionf , R

2 = 0.42

NE Female Walleye Life History Relationships

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 ConditionPredicted Relative Conditionf = 1.07 Observed Relative Conditionf = 1.06

Length at maturation (mm)Predicted Lmf = 457mm Observed Lmf = 448mm

Potential population increase (r')Predicted r' = 3.85 Observed r' = 2.83 to 3.03

Asymptotic length (mm)Predicted L = 775mm Observed L = 792mm

Gonadosomatic index (%)Predicted GSIf = 4.43% NO DATA COLLECTED

Visceral fat index (%)Predicted VFIf = 2.62% NO DATA COLLECTED

Lake Temagami Female Walleye

Lake Temagami Walleye StatusLake Temagami Walleye Status

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

Any Questions or Comments?Any Questions or Comments?