Life history variation among four shallow water morphotypes of Lake - - PowerPoint PPT Presentation

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Life history variation among four shallow water morphotypes of Lake - - PowerPoint PPT Presentation

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Life history variation among four shallow water morphotypes of Lake Trout from Great Bear Lake, NT Louise Chavarie 1 , K. Howland 2 , P. Venturelli 3 , B. Kissinger 2,4 , R. Tallman 2 , and W. Tonn 1 . 1 Dept. of Biological Sciences,

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Louise Chavarie1, K. Howland2, P. Venturelli3, B. Kissinger2,4, R. Tallman2, and W. Tonn1.

  • 1Dept. of Biological Sciences, University of Alberta, Canada
  • 2Dept. of Fisheries and Oceans, Freshwater Institute, Canada
  • 3Dept. of Fisheries, Wildlife and Conservation Biology, University of Minnesota, US
  • 4Dept. of Biological Sciences, University of Manitoba, Canada

Life‐history variation among four shallow‐water morphotypes of Lake Trout from Great Bear Lake, NT

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Introduction

Lake Trout

Salmonid, Salvelinus (char) Northern distribution Cold-adapted species Low intraspecific diversity

http://www.roughfish.com/lake‐trout http://pblabs.biology.dal.ca

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Typical System: depth partitioning Siscowet and/or Humper (deep-water) Piscivores (shallow-water) Generally restricted to large & deep lakes (e.g., Lake Superior, Lake Mitassini, Great Slave Lake)

Lake Trout

Introduction (Eshenroder, 2008)

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Lake Characteristics:

  • Northern Canada
  • Surface = 32 000 km2 with 5 arms
  • Deep (mean = 90 m, max = 450 m)
  • Relative simple food web = 15 fish species
  • Cold monomictic, essentially isothermal (8‐12 oC)
  • Ultra‐oligotrophic (Secchi depth ~30 m)
  • Pristine

Great Bear Lake, NT

Study area

1 arm per year=12 yrs

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Morphology Life‐history ? Diet

Photo credit: B. Kissinger

Chavarie et al., 2013 Chavarie et al., 2014a Chavarie et al., 2014b Generalist Piscivore Benthic Pelagic

Lake Trout Polymorphism

Study area

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Life‐history

Age distributions Length distributions

Kruskal‐Wallis=87.05, df=3, p < 0.001 Kruskal‐Wallis=27.33, df=3, p < 0.001

9 ‐ 60 years 450 ‐ 1136 mm Remarkable longevity Remarkable sizes

65

N=902 Chavarie et al., 2014, submitted

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Life‐history

Back‐calculation

  • Dimorphism in otoliths

Morph 1: n=39 - 484-750 mm - 12-43 years Morph 2 : n= 30 - 545-1136 mm - 15-49 years Morph 3: n = 40 - 554-751 mm - 17-53 years Morph 4: n= 23 - 545-803 mm - 14-45 years

Relationship between fish length and otolith length depended on morph. Morph 2 = realistic y‐intercept Morphs 1, 3 and 4 = unrealistically large y‐intercepts

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Life‐history

Morph 2 biological intercept method Morphs 1, 3 and 4 combined the biological intercept and Fraser-Lee methods

Due to divergence from normal otolith growth, incorporated morph-specific y- intercepts that more accurately described

  • bserved reductions in fish growth.

200 400 600 800 1000 1200 0.5 1 1.5 2 Fish Length (mm) Otolith Length (mm)

= generalist X = piscivores = benthic =pelagic

Back‐calculation

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Mean back-calculated (mm) Age (years)

Biphasic model

Morph 1: n=37 Morph 2 : n= 44 Morph 3: n = 45 Morph 4 n= 33 Wi values (AIC): evaluate est. ages‐at‐maturity Life‐history Juvenile Adult

AIC weight (Wi)

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Morph Age‐at‐ maturity (yrs) Length‐at‐ maturity (mm) Immature growth rate Adult growth rate (K) Reproduction investment Adult L∞

1 17.4 593.4 22.2 0.030 0.090 740.8 2 20.2 703.7 22.1 0.016 0.048 1371.9 3 18.6 581.7 22.3 0.028 0.086 773.7 4 20.2 640.9 22.0 0.027 0.081 809.6

Life‐history

Biphasic model: results

Classical life‐history trade‐off Comparable to piscivore life‐history Intermediate = Comparable to large benthic morph of Arctic Char? Intermediate = surprising for the most specialized diet?

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0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09

Immature Growth (mm/ Degree Days)

0.0 0.1 0.2 0.3 10 20 30 40 2,000 12,000 22,000 32,000

Degree-days-at-maturity

0.0 0.1 0.2 10 20 30

Count

Morph Age‐at‐ maturity Length‐at‐ maturity Adult L∞

1 17.4 593.4 740.8 2 20.2 703.7 1371.9 3 18.6 581.7 773.7 4 20.2 640.9 809.6 South 7.3 454 647 North 10.4 439 647

Biphasic model

McDermid et al., 2010 Life‐history

Degree-days above 0°C to account for among- population differences in annual temperature

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Proportions spawners, resting females & males

Life‐history

X2= = 62.40, df = 9, p < 0.01

Life‐history adaptation to northern latitude?

  • Poor nutrition

latitude

  • Species with high longevity

Almost 50% are resting individuals

Skip spawning Life‐history

FR

Female‐spawner Female‐resting Male‐spawner Male‐resting

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SLIDE 13

Summary

  • 4 morphotypes in shallow-water of Great Bear

Lake.

Conclusion

Siscowet or/and Humper (deep-water) Piscivores (shallow-water)

Typical System: depth partitioning New perspectives on the current model of Lake Trout polymorphism Great Bear Lake

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SLIDE 14

Summary

Conclusion

  • Trade-off between somatic and

reproductive investment Juvenile growth

Age‐at‐maturity Length‐at‐maturity Longevity

  • Reproduction tactics varied
  • High proportion of resting individuals
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SLIDE 15

Chapter 5

Question ???