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Age and Growth. Growth & age patterns Measurement techniques. Indeterminate. Determinate. Size. Age. Growth patterns. Determinate Growth Mammals & birds Indeterminate Growth Fishes. Indeterminate growth & fecundity. Fish growth – von Bertalanffy equation. L t =L max (1-e -kt ).

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slide1

Age and Growth

Growth & age patterns

Measurement techniques

growth patterns

Indeterminate

Determinate

Size

Age

Growth patterns
  • Determinate Growth
    • Mammals & birds
  • Indeterminate Growth
    • Fishes
growth patterns8
Growth patterns
  • Great Plasticity in growth
  • Size at age: High variability
    • Between species
    • Between populations
    • Between individuals
environmental factors influencing growth
Environmental factors influencing growth
  • Temperature
  • Food and Nutrient Availability
  • Light Regime
  • Oxygen Concentration
  • Salinity
  • Pollutants
  • Predator Densities
  • Intraspecific Social Interactions
  • Genetics
example species polymorphism
Example: Species polymorphism

Large benthic feeder

Small benthic feeder

Piscivorous feeder

Salmonidae

Artic Charr

Salvelinus alpinus

Planktivorous feeder

age measurement methods
Age measurement methods
  • Scales
  • Otoliths
  • Vertebrae
  • Rays/Spines
otolith uses
Otolith uses
  • Age determination
    • Daily ring counts
    • Annual ring counts
    • Radioactive isotopes
  • Species identification
  • Paleoclimate studies (018)
  • Life history studies (elemental tracers)
slide25

Age calculation error case

Scales: 3-8 years

Otoliths: 4-40 & up to 80

Anoplomatidae

Sablefish

Anoplopoma fimbria

slide29

Climate studies (isotope 018)

(6000 year old fossil)

slide31

Elemental tracers

of weakfish

Thorrold et al. 2001

slide33

Proof of Natal Homing!

Thorrold et al. 2001

how do populations change
How do populations change?
  • Nt+1 = Nt + B – D + I – E
  • B = births
  • D = deaths
  • I = immigration
  • E = emigration

Immigration

Stocking

Population

Births

Deaths

Angling

Emigration

survival
Survival

Eggs and larvae suffer the largest losses

HATCH

Recruit!

2 cohorts each produce 10,000,000 eggs

90.5% survivorship/day yields 24,787 survivors at 60 days

95.1% survivorship/day yields 497,871 survivors at 60 days

recruitment
Recruitment
  • Can mean many things!
    • Number of young-of-year (YOY) fish entering population in a year
    • Number of fish achieving age/size at which they are vulnerable to fishing gear
  • Somewhat arbitrary, varies among populations
  • Major goal of fish population dynamics: understanding the relationship between stock size and recruitment
slide38

What determines recruitment?

-Stock size (number and size of females)

slide39

spawning stock biomass (SSB)

Density-independent

Ricker

What determines recruitment?

Beverton-Holt

From: Wootton (1998). Ecology of teleost fishes.

slide40

spawning stock biomass (SSB)

Density-independent

Ricker

What determines recruitment?

Beverton-Holt

From: Wootton (1998). Ecology of teleost fishes.

slide41

spawning stock biomass (SSB)

Density-independent

Ricker

What determines recruitment?

Beverton-Holt

From: Wootton (1998). Ecology of teleost fishes.

the problem
The problem?

Stochasticity = variable recruitment!

slide43

From: Cushing (1996). Towards

a science of recruitment in fish

populations

slide44

Highly variable recruitment results in naturally very variable catches

From: Jennings, Kaiser and Reynolds (2001). Marine Fisheries Ecology

population abundance
Population Abundance

On rare occasions, abundance can be measured directly

Small enclosed systems

Migration

catch per unit effort cpue
Catch per unit effort (CPUE)

1

Catch= 4 fish

CPUE=4/48=0.083

Effort= 4 nets for 12 hours each= 48 net hours

2

Catch=8 fish

CPUE=8/48=0.167

Effort= 4 nets for 12 hours each= 48 net hours

We conclude population 2 is 2X larger than population 1

Very coarse and very common index of abundance

estimates of population size
Estimates of Population Size
  • Proportional sampling
  • Rp = size of the range of the population (Rp), (uniform distribution)
  • Rs = size of sampling a region
  • Ns/Np = Rs/Rp.
  • Np = (Ns Rp)/Rs = Population Abundance

No Accuracy Estimate

population abundance48
Population abundance

Density estimates (#/area)

Eggs estimated with quadrats

Pelagic larvae sampled with modified plankton nets

Juvenile and adult fish with nets, traps, hook and line, or electrofishing

Density is then used as index of abundance, or multiplied by habitat area to get abundance estimate

depletion methods
Depletion methods

Closed population

Vulnerability constant for each pass

Collection efficiency constant

Often not simple linear regression

*

*

Number Caught

*

*

Number previously caught

estimates of population size50
Estimates of Population Size
  • Mark & Recapture

capture – mark – release - recapture

  • Np = population abundance
  • M = number of individuals that are marked
  • n = size of the second sample of organisms
  • R: number of marked organisms in second sample

Np = (M*n)/R

Accuracy Estimates Available

mark recapture
Mark recapture

M=5

C=4

R=2

N=population size=????

modified petersen method
Modified Petersen method
  • Assumptions:
    • Closed population
    • Equal catchability in first sample
    • Marking does NOT influence catchability
      • Marked and unmarked fish mix randomly
      • Mortality rates are equal
    • Marks are not lost
schnabel method
Schnabel method
  • Closed population
  • Equal catchabilty in first sample
  • Marking does NOT influence catchability
  • Multiple recaptures
    • Easier to pick up on violation of assumptions