Iteroparity and Steelhead: what we know and dont know

1
Iteroparity and Steelhead what we know and dont
know

• John R. McMillan
• Oregon State University

2
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)

3
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)

4
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

5
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

6
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)

7
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)

8
Latitudinal Distribution of Repeat Spawn Rates
for Steelhead
Derived largely from Busby et al. 1996
Russia
Washington - Oregon
AK - Canada
North
South
9
Why is Iteroparity Important?

• Recruitment
• First-time spawners dont 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)

10

• 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)

11
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)

12

• 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)

13
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

14
(No Transcript)