Iteroparity and steelhead what we know and don t know
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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)


Latitudinal Distribution of Repeat Spawn Rates for Steelhead

Derived largely from Busby et al. 1996

Russia

AK - Canada

Washington - Oregon

North

South


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)


  • 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)


  • 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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