Yellowfin tuna

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Yellowfin tuna Mature at age 3 Females expend 2
body mass / day on egg production Achieve body
size up to 100 kg
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Boccacio Rockfish Max. Size, 75-91 cm, Max
weight 6.8 kg Life Expectancy 50 100
years Internal live bearer (20,000 200,000
eggs)
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Pacific Halibut Reach sizes up to 2.5 m, gt 300
kg Live approximately 30 years Fecundity
100,0002,800,000 per year
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Atlantic Silverside Maximum size of 15
cm Annual species, mature at age 1, few survive
to age 2 Fecundity 5,000 13,000 eggs
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Spiny Dogfish Maximum age 75 years Mature at
age 30 Ovoviviparous Pups are 18 30 cm at
birth Females produce fewer than 10 pups over a 2
year period
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Life Histories of Marine Fishes

• Basic theories
• Empirical patterns of life history
  characteristics
• Life history invariants
• Phenotypic plasticity
• Fishing effects on life history characteristics

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What is life history

• Pattern of reproduction and longevity over the
  course of an individuals lifetime
• What does that mean??!???!!??

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Creating the Super-Fish

• Suppose you could create any fish you wanted
• You wanted to make one that would be as
  successful as possible
• What attributes would you give it?

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The superfish cant exist

• There are trade-offs between life history
  strategies
• High growth is usually associated with high
  mortality
• Egg size vs. egg number
• Large body size vs. time to maturity
• Reproductive output and mortality

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Categories of constraints

• Physiological
• Egg production vs. care / size
• Ecological
• Body size vs. trophic position
• Demographic
• Intrinsic rate of population growth vs. age at
  maturity
• Phylogenetic

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Basic Theory Age-at-Maturation

• Assumptions
• (1) Individuals choose an amount of effort to
  allocate to reproduction.
• 0 100
• The lifetime reproductive success is the sum of
  present plus expected future reproductive
  success
• RS lifetime RS present RS future
• Both RS present and RS future depend on effort
  allocated now

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Example Concave RS Functions
This individual will allocate an intermediate
amount of energy to reproduction Will reproduce
many times (has both present and future
reproductive success) Iteroparous
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Example Convex RS functions
Optimal solution is always All or
nothing Commonly leads to either no present or
no future reproductive success i.e. Species
reproduces once and then has no future RS
Semelparity
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Age at reproduction Semelparous Species

• Imagine that present RS depends on your body size
• Body size increase with age
• At some age, the optimal effort allocation will
  be 100

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Age 2
Age 3
Age 4
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When should maturation be delayed?
(1) High growth rates (2) High costs of
reproduction (3) Low mortality rates

• These all affect the Future RS curve
• and (3) make the y-intercept higher
• (2) Makes the function decline more steeply

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Tests of Expectations

• Schaffer and Elson, 1975. The adaptive
  significance of variations in life history among
  local populations of Atlantic salmon in North
  America. Ecology 56 577-590
• Alantic salmon iteroparous
• Gradient of reproductive effort required river
  length

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Predictions

• Environmental factors increasing reproductive
  success per unit effort will select for
• Greater reproductive effort (all ages)
• Earlier age at reproduction
• Increased post-breeding survival will select for
• Reduced effort (all ages)
• Later age at first reproduction

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Weight-at-Reproduction vs. Migration Distance
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Fishing and growth seem to alter the pattern
Suggests unique ocean migrations Little benefit
of delayed maturation for Newfoundland
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Delayed maturation for fast growing fish
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Empirical Patterns

• Winemiller and Rose (1992). Patterns of
  life-history diversification in North American
  fishes Implications for population regulation.
  Can. J. Fish. Aquat. Sci. 49 2196-2218
• Looked at 16 life history characteristics
• Looked for patterns corresponding to
• Habitat
• Trophic Level
• Reproductive Behavior

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Marine vs. Freshwater Comparison
Marine fishes tend to Mature later Have large
body sizes Have larger clutch sizes Show less
parental care Have smaller eggs Reproduce for
more seasons
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Visualizing Trade-offs
Three main constraints Juvenile
survivorship Fecundity Age at maturation
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Three endpoint strategies

• Opportunistic
• Early age to maturation, high juvenile mortality,
  small body size, low parental care
• Equilibrium
• High parental care (or large eggs), intermediate
  body size
• Periodic
• Low parental care, long lived, high fecundity,
  multiple spawnings, large body size, late age at
  maturation

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Correlations with other traits
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Other Empirical Approaches

• Life history invariants ratios of life history
  traits that appear to be constant across taxa
• Originally explored by Ray Beverton and Sidney
  Holt
• Expanded by Eric Charnov

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First, some definitions

• Often relate fish size to fish age using a
  von-bertalanffy growth function

Mass
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Also, the probability of surviving to an age
declines
P(survive to age t) exp (-M t) M natural
mortality rate
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Putting these two together
An optimal strategy, given these growth and
maturity parameters, would be to mature at about
age 6
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Beverton and Holt Invariants

• M x Tm
• Mortality rate times age at maturation
• Lm / L
• Length at maturation relative to maximum length
• M / K
• Mortality rate relative to growth rate

These are called invariants because the ranges
of observed values are limited BUT, we also use
these to distinguish between life history
strategies
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Beverton Growth-Longevity- Maturity Plots

• Relate life history invariants to each other

Species A Species B
Lm / L
K / M
Or, K Tmax (because M 1/Tmax)