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Iteroparity and Steelhead: what we know and don’t know. John R. McMillan Oregon State University. Introduction to Reproduction. Reproductive strategies (big bang v. bet-hedge) Annual strategy in plants and semelparous strategy in animals Reproduce one time

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iteroparity and steelhead what we know and don t know

Iteroparity and Steelhead: what we know and don’t know

John R. McMillan

Oregon State University

introduction to reproduction
Introduction to Reproduction
  • Reproductive strategies (big bang v. bet-hedge)
    • Annual strategy in plants and semelparous strategy in animals
      • Reproduce one time
    • Perennial strategy in plants and iteroparous strategy in animals
      • Reproduce more than one time
  • Salmonid species
    • Pacific salmon – semelparous (Altukhov et al. 2000)
    • All other species – iteroparous (Wilson 1997)
introduction to reproduction1
Introduction to Reproduction
  • Reproductive strategies (big bang v. bet-hedge)
    • Annual strategy in plants and semelparous strategy in animals
      • Reproduce one time
    • Perennial strategy in plants and iteroparous strategy in animals
      • Reproduce more than one time
  • Salmonid species
    • Pacific salmon – semelparous (Altukhov et al. 2000)
    • All other species – iteroparous (Wilson 1997)
selection and traits
Selection and Traits
  • Life history theory (Stearns 1976; Charlesworth 1994; Crespi and Teo 2002)
    • Semelparity
      • Select for higher juvenile survival
        • Increased egg size
      • Select for no adult survival
        • Increased investment in egg weight, female nest guarding, secondary sexual characteristics, breed under higher densities
    • Iteroparity
      • Low or inconsistent juvenile survival
        • Smaller egg size
      • High adult survival
        • Reduced investment in eggs, secondary sexual characteristics, lower breeding density, and no female nest guarding
selection and traits1
Selection and Traits
  • Life history theory (Stearns 1976; Charlesworth 1994; Crespi and Teo 2002)
    • Semelparity
      • Select for higher juvenile survival
        • Increased egg size
      • Select for no adult survival
        • Increased investment in egg weight, female nest guarding, secondary sexual characteristics, breed under higher densities
    • Iteroparity
      • Select for lower juvenile survival
        • Smaller egg size
      • Select for higher adult survival
        • Reduced investment in egg weight, secondary sexual characteristics, no female nest guarding, breed under lower densities
steelhead patterns
Steelhead Patterns
  • Steelhead
    • One-time reproduction generally most common
      • Highly variable rates of repeat spawning (0 – 79 %)
    • Iteroparous individuals
      • Typically female (Burgner et al. 1992; Wertheimer and Evans 2005)
      • Typically smaller sized (Teo and Crespi 2002; Hendry and Stearns 2004)
      • More common in ocean-maturing life history (Busby et al. 1996)
  • Latitude and distance from sea
    • Highest levels at latitudinal extremes(e.g., Russia, Savvaitova et al. 1999; South America, Riva-Rossi 2007)
        • Similar observations for Atlantic salmon (Jonsson and Jonsson 2004)
        • Perhaps because energy consumption increases with water temperature
    • Lowest levels appear to be in furthest inland populations(Meehan and Bjornn 1991; Narum et al. 2008)
steelhead patterns1
Steelhead Patterns
  • Steelhead
    • One-time reproduction generally most common
      • Highly variable rates of repeat spawning (0 – 79 %)
    • Iteroparous individuals
      • Typically female (Burgner et al. 1992; Wertheimer and Evans 2005)
      • Typically smaller sized (Teo and Crespi 2002; Hendry and Stearns 2004)
      • More common in ocean-maturing life history (Busby et al. 1996)
  • Latitude and distance from sea
    • Highest levels at latitudinal extremes(e.g., Russia, Savvaitova et al. 1999; South America, Riva-Rossi 2007)
        • Similar observations for Atlantic salmon (Jonsson and Jonsson 2004)
    • Lowest levels appear to be in furthest inland populations(Meehan and Bjornn 1991; Busby et al. 1996; Narum et al. 2008)
slide8

Latitudinal Distribution of Repeat Spawn Rates for Steelhead

Derived largely from Busby et al. 1996

Russia

AK - Canada

Washington - Oregon

North

South

slide9

Why is Iteroparity Important?

  • Recruitment
      • First-time spawners don’t always replace themselves (e.g., Waddell Creek, Keogh River; Hal Michael, personal communication)
      • Repeat spawners in Atlantic salmon can produce disproportionate share of recruitment (Chadwick 1987; Mills 1989)
slide10
Fitness
    • Increased lifetime fitness
      • Greater fecundity
      • Repeat spawning female steelhead produced twice as many offspring as one-time spawners (Seamons et al., in prep)
    • Spread risk over multiple generations (Fleming and Reynolds 2004; Hendry and Stearns 2004)
what human factors influence iteroparity
What Human Factors Influence Iteroparity?
  • Environment
    • Habitat conditions experienced by adults during return to ocean
      • Dams
      • Climate
      • Oversummering habitat in some cases
  • Sport and commercial fisheries
    • Level of adult exploitation and encounter rates during return to ocean
      • Selection against larger fish could select against iteroparous individuals
        • This has been suggested to have occurred in Atlantic salmon (see Jonsson and Jonsson 2004)
slide12
Fisheries
    • Sport
      • Rate of adult exploitation & encounter by sport anglers during return to ocean?
        • Energy expenditure
    • Commercial
      • Selection against larger fish could select against iteroparous individuals
        • This has been suggested to have occurred in Atlantic salmon (see Jonsson and Jonsson 2004)
patterns processes uncertainties
Patterns, Processes, Uncertainties
  • Lots of hypotheses, little data
    • Does iteroparity matter?
    • What causes iteroparity?
      • Natural v. human influences
    • How does this factor into our management regimes?
      • Abundance v. diversity
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