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

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

Lake Trout http://pblabs.biology.dal.ca Salmonid, Salvelinus (char) Northern distribution Cold-adapted species Low intraspecific diversity http://www.roughfish.com/lake ‐ trout Introduction

Lake Trout Typical System: depth partitioning (Eshenroder, 2008) Piscivores (shallow-water) Siscowet and/or Humper (deep-water) Generally restricted to large & deep lakes (e.g., Lake Superior, Lake Mitassini, Great Slave Lake) Introduction

Great Bear Lake, NT Lake Characteristics: • Northern Canada • Surface = 32 000 km 2 with 5 arms 1 arm per year=12 yrs • Deep (mean = 90 m, max = 450 m) • Relative simple food web = 15 fish species • Cold monomictic, essentially isothermal (8 ‐ 12 o C) • Ultra ‐ oligotrophic (Secchi depth ~30 m) • Pristine Study area

Morphology Lake Trout Polymorphism Generalist Diet Life ‐ history ? Piscivore Benthic Photo credit: B. Kissinger Chavarie et al., 2014b Pelagic Chavarie et al., 2013 Study area Chavarie et al., 2014a

Age distributions Length distributions 9 ‐ 60 years Remarkable longevity Remarkable sizes 450 ‐ 1136 mm N=902 65 Kruskal ‐ Wallis=27.33, df =3, p < 0.001 Kruskal ‐ Wallis=87.05, df =3, p < 0.001 Life ‐ history Chavarie et al., 2014, submitted

Back ‐ calculation 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  Dimorphism in otoliths Relationship between fish length and otolith length depended on morph. Morph 2 = realistic y ‐ intercept Morphs 1, 3 and 4 = unrealistically large y ‐ intercepts Life ‐ history

Back ‐ calculation Morph 2 biological intercept method Morphs 1, 3 and 4 combined the biological intercept and Fraser-Lee methods 1200 = generalist 1000 Fish Length (mm) X = piscivores 800 Due to divergence from normal otolith = benthic 600 growth, incorporated morph-specific y- =pelagic 400 intercepts that more accurately described 200 observed reductions in fish growth. 0 0 0.5 1 1.5 2 Life ‐ history Otolith Length (mm)

Biphasic model Wi values (AIC): Mean back-calculated (mm) evaluate est. ages ‐ at ‐ maturity Morph 1: n=37 Morph 2 : n= 44 (Wi) AIC weight Adult Juvenile Morph 4 n= 33 Morph 3: n = 45 Age (years) Life ‐ history

Biphasic model: results Morph Age ‐ at ‐ Length ‐ at ‐ Immature Adult Reproduction Adult L ∞ maturity maturity growth rate growth rate investment (yrs) (mm) (K) 1 17.4 593.4 22.2 0.030 0.090 740.8 Classical life ‐ history trade ‐ off 2 20.2 703.7 22.1 0.016 0.048 1371.9 Comparable to piscivore life ‐ history 3 18.6 581.7 22.3 0.028 0.086 773.7 Intermediate = Comparable to large benthic morph of Arctic Char? 4 20.2 640.9 22.0 0.027 0.081 809.6 Intermediate = surprising for the most specialized diet? Life ‐ history

Morph Age ‐ at ‐ Length ‐ at ‐ Adult L ∞ maturity maturity Biphasic model 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 7.3 454 647 South McDermid et al., 2010 10.4 439 647 North 40 0.3 30 0.2 30 Degree-days above 0°C to 0.2 20 Count account for among- 20 0.1 population differences in 0.1 10 10 annual temperature 0 0.0 0 0.0 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 0.09 2,000 12,000 22,000 32,000 Immature Growth (mm/ Degree Days) Degree-days-at-maturity Life ‐ history

Life ‐ history Proportions spawners, Almost 50% are resting individuals resting females & males Skip spawning FR Life ‐ history adaptation to northern latitude?  Poor nutrition latitude  Species with high longevity X 2 = = 62.40, df = 9, p < 0.01 Female ‐ resting Male ‐ spawner Male ‐ resting Female ‐ spawner Life ‐ history

Summary  4 morphotypes in shallow-water of Great Bear Lake. Typical System: depth partitioning Piscivores (shallow-water) Siscowet or/and Humper (deep-water) Great Bear Lake New perspectives on the current model of Lake Trout polymorphism Conclusion

Summary  Trade-off between somatic and reproductive investment Age ‐ at ‐ maturity Juvenile growth Length ‐ at ‐ maturity Longevity  Reproduction tactics varied  High proportion of resting individuals Conclusion

Question ??? Chapter 5