Reproduction

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Reproduction

• Reading Chapter 9 (9.3)
• Fecundity
• Reproductive potential
• Maturity
• Sex ratio
• Cunner example

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Reproduction

• High fecundity

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Reproduction

• High fecundity
• 96 of marine fish have pelagic eggs/larvae

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Reproduction

• High fecundity
• 96 of marine fish have pelagic eggs/larvae
• Fecundity varies from few to millions/year

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Reproduction

• High fecundity
• 96 of marine fish have pelagic eggs/larvae
• Fecundity varies from few to millions/year
• Some are born mature (dwarf perch),

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Reproduction

• High fecundity
• 96 of marine fish have pelagic eggs/larvae
• Fecundity varies from few to millions/year
• Some are born mature, others mature in first year
  (anchovies, silversides, tomcod)

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Reproduction

• High fecundity
• 96 of marine fish have pelagic eggs/larvae
• Fecundity varies from few to millions/year
• Some are born mature, others mature in first
  year, others mature decade(s) after hatching
  (sturgeon, redfish)

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Reproduction

• High fecundity
• 96 of marine fish have pelagic eggs/larvae
• Fecundity varies from few to millions/year
• Some are born mature, others mature in first
  year, others mature decade(s) after hatching
• Fecundity and maturity schedules have profound
  effects on stock dynamics and harvesting

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Reproduction

• Gonads, testes and ovaries, have long inactive
  periods

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Reproduction

• Gonads, testes and ovaries, have long inactive
  periods
• Spawning is when fully developed gametes are
  released

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Reproduction

• Gonads, testes and ovaries, have long inactive
  periods
• Spawning is when fully developed gametes are
  released
• Spawning often takes place in particular habitats
  at particular times

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Reproduction

• Gonads, testes and ovaries, have long inactive
  periods
• Spawning is when fully developed gametes are
  released
• Spawning often takes place in particular habitats
  at particular times
• Stimulus may be internal (endogenous) or

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Reproduction

• Gonads, testes and ovaries, have long inactive
  periods
• Spawning is when fully developed gametes are
  released
• Spawning often takes place in particular habitats
  at particular times
• Stimulus may be internal (endogenous) or external
  (exogenous)

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Fecundity

• Total count of ova in both ovaries

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Fecundity

• Total count of ova in both ovaries
• Increases with age in teleosts

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Fecundity

• Total count of ova in both ovaries
• Increases with age in teleosts
• Related to a power of length or weight

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Fecundity

• Total count of ova in both ovaries
• Increases with age in teleosts
• Related to a power of length or weight
• Fa Lb

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Fecundity

• Total count of ova in both ovaries
• Increases with age in teleosts
• Related to a power of length or weight
• Fa Lb
• and
• ln Flna b ln L

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Phoxinus phoxinus (common minnow)
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Log Fecundity
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Log Fecundity
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age
weight
length
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Fecundity

• Functional fecundity
• actual production of viable oocytes

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Fecundity

• Functional fecundity
• actual production of viable oocytes
• True fecundity
• total number of eggs produced

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Fecundity

• Functional fecundity vs.
• True fecundity
• Differences due to?

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Fecundity

• Functional fecundity vs.
• True fecundity
• Differences due to
• incomplete spawning

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Fecundity

• Functional fecundity vs.
• True fecundity
• Differences due to
• incomplete spawning
• atresia (degeneration)

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Fecundity

• Functional fecundity vs.
• True fecundity
• Differences due to
• incomplete spawning
• atresia (degeneration)
• resorption of oocytes

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Fecundity

• determinate vs.
• indeterminate spawners?

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Fecundity

• determinate
• all eggs to be spawned present as oocytes in
  ovary prior to spawning

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Fecundity

• indeterminate
• eggs to be spawned not all present as oocytes in
  ovary prior to spawning (some develop later)

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Fecunditydeterminate vs indeterminate spawners

• implications for fecundity estimation?

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Fecunditydeterminate vs indeterminate spawners

• implications for fecundity estimation? In
  indeterminate spawners
• Counts of eggs do not indicate annual fecundity

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Fecunditydeterminate vs indeterminate spawners

• implications for fecundity estimation? In
  indeterminate spawners
• Counts of eggs do not indicate annual fecundity
• Continuous new batches (size distribution)

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Fecunditydeterminate vs indeterminate spawners

• implications for fecundity estimation? In
  indeterminate spawners
• Counts of eggs do not indicate annual fecundity
• Continuous new batches (size distribution)
• Protracted season

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Fecunditydeterminate vs indeterminate spawners

• implications for fecundity estimation?
• Multiple spawning does not indicate indeterminate
  status!

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determinate
bimodal
indeterminate
continuous
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Fecunditymethodology

• A sub-sample of the ovary is taken

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Fecunditymethodology

• A sub-sample of the ovary is taken and
  extrapolated to total counts.

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Fecunditymethodology

• A sub-sample of the ovary is taken and
  extrapolated to total counts.
• This avoids total counts but introduces error

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Fecunditymethodology

• A sub-sample of the ovary is taken and
  extrapolated to total counts.
• This avoids total counts but introduces error
• How representative is the sample?

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Fecunditymethodology

• A sub-sample of the ovary is taken and
  extrapolated to total counts.
• This avoids total counts but introduces error
• How representative is the sample?
• location

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Fecunditymethodology

• A sub-sample of the ovary is taken and
  extrapolated to total counts.
• This avoids total counts but introduces error
• How representative is the sample?
• location
• egg size variability

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Fecunditymethodology

• A sub-sample of the ovary is taken and
  extrapolated to total counts.
• This avoids total counts but introduces error
• How representative is the sample?
• location
• egg size variability
• egg quality variability

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Fecunditymethodology

• Using population fecundity as a measure of
  reproductive potential assumes
• linear relationship between fish size and
  fecundity

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Fecunditymethodology

• Using population fecundity as a measure of
  reproductive potential assumes
• linear relationship between fish size and
  fecundity
• constant annual sex ratio

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Fecunditymethodology

• Using population fecundity as a measure of
  reproductive potential assumes
• linear relationship between fish size and
  fecundity
• constant annual sex ratio
• no annual variation in egg -fish size
  relationship

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Fecunditymethodology

• Using population fecundity as a measure of
  reproductive potential assumes
• linear relationship between fish size and
  fecundity
• constant annual sex ratio
• no annual variation in egg -fish size
  relationship
• no annual variation in age/size at maturity

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Fecunditymethodology

• Using population fecundity as a measure of
  reproductive potential assumes
• linear relationship between fish size and
  fecundity
• constant annual sex ratio
• no annual variation in egg -fish size
  relationship
• no annual variation in age/size at maturity
• egg is a function of fish size independent of
  age

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Fecunditymethodology

• Using population fecundity as a measure of
  reproductive potential assumes
• linear relationship between fish size and
  fecundity
• constant annual sex ratio
• no annual variation in egg -fish size
  relationship
• no annual variation in age/size at maturity
• egg is a function of fish size independent of
  age
• no annual variation in proportion of eggs
  retained by the female during spawning

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Fecunditydensity-dependence

• At high population densities females can retain
  eggs

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Fecunditydensity-dependence

• At high population densities females can retain
  eggs
• At low densities females may become more fecund

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Fecunditydensity-dependence

• At high population densities females can retain
  eggs
• At low densities females may become more fecund
• Density-dependent and compensatory responses
  (stable)

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Fecunditydensity-dependence

• At low population densities females may retain
  eggs

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Fecunditydensity-dependence

• At low population densities females may retain
  eggs if stimulus is absent

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Fecunditydensity-dependence

• At low population densities females may retain
  eggs if stimulus is absent
• Depensatory (unstable)

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Maturity

• Maturity schedules age-dependent

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Maturity

• Maturity schedules age-dependent
• Examined by classifying ovaries into
  developmental stages (color, appearance, or
  histology)

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Staged development of mackerel eggs
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Maturitygonosomatic indices

• GSI used to track reproductive cycle

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Maturitygonosomatic indices

• GSI used to track reproductive cycle
• assumes ovary increases with size with increasing
  development

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Maturitygonosomatic indices

• GSI used to track reproductive cycle
• assumes ovary increases with size with increasing
  development
• compares gonad mass (GM) to total mass (TM)
• GSI 100 (GM/TM)

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GSI
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GSI
IM
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GSI
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Maturitylength at maturity

• Although spawning is dependent on abiotic
  factors, age/size also important

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Maturitylength at maturity

• Although spawning is dependent on abiotic
  factors, age/size also important
• Length (Lm) or age (Tm) at maturity is length/age
  when 50 of population is mature

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Maturitylength at maturity

• Although spawning is dependent on abiotic
  factors, age/size also important
• Length (Lm) or age (Tm) at maturity is length/age
  when 50 of population is mature
• by estimating mature in each size class

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Maturitylength at maturity

• Although spawning is dependent on abiotic
  factors, age/size also important
• Length (Lm) or age (Tm) at maturity is length/age
  when 50 of population is mature
• by estimating mature in each size class
• fitting a logistic curve
• P 1/(1exp-r(L- Lm))

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Maturitylength at maturity

• Although spawning is dependent on abiotic
  factors, age/size also important
• Length (Lm) or age (Tm) at maturity is length/age
  when 50 of population is mature
• by estimating mature in each size class
• fitting a logistic curve
• P 1/(1exp-r(L- Lm))
• Or when linearized
• ln (1-P/P) r Lm- rL

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knife-edge
American lobster
ogive
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Maturitylife histories

• species-specific maturity schedules

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winter flounder
striped bass
shortnose sturgeon
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Maturitylife histories

• species-specific maturity schedules
• semelparity vs iteroparity

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Maturitylife histories

• species-specific maturity schedules
• semelparity vs iteroparity
• How often?

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Maturitylife histories

• species-specific maturity schedules
• semelparity vs iteroparity
• protogyny vs protandry

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Maturitylife histories

• species-specific maturity schedules
• semelparity vs iteroparity
• protogyny vs protandry
• density-dependence

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Maturitylife histories

• species-specific maturity schedules
• semelparity vs iteroparity
• protogyny vs protandry
• density-dependence
• sex ratios

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Maturitylife histories

• species-specific maturity schedules
• semelparity vs iteroparity
• protogyny vs protandry
• density-dependence
• sex ratios
• females usually modeled

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Maturitylife histories

• species-specific maturity schedules
• semelparity vs iteroparity
• protogyny vs protandry
• density-dependence
• sex ratios
• females usually modeled
• important if spawning biomass is needed

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Maturitylife histories

• species-specific maturity schedules
• semelparity vs iteroparity
• protogyny vs protandry
• density-dependence
• sex ratios
• females usually modeled
• important if spawning biomass is needed, or if
  males are limiting to reproductive success

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Maturitylife histories

• species-specific maturity schedules
• semelparity vs iteroparity
• protogyny vs protandry
• density-dependence
• sex ratios
• females usually modeled
• important if spawning biomass is needed, or if
  males are limiting to reproductive success
• distinguishing sexes often difficult externally