Age and Growth
Growth & age patterns
Measurement techniques
Growth patterns
• Determinate Growth
– Mammals & birds
• Indeterminate Growth
– Fishes
Indeterminate
Size
Determinate
Age
Indeterminate growth &
fecundity
Fish growth – von Bertalanffy
equation
Lt=Lmax(1-e-kt)
Fish growth – von Bertalanffy
equation
Length – Weight relation (power function)
W=a Lb
Growth patterns
• Great Plasticity in growth
• Size at age: High variability
– Between species
– Between populations
– Between individuals
Environmental factors
influencing growth
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Temperature
Food and Nutrient Availability
Light Regime
Oxygen Concentration
Salinity
Pollutants
Predator Densities
Intraspecific Social Interactions
Genetics
Example: Species polymorphism
Large benthic feeder
Small benthic feeder
Piscivorous feeder
Salmonidae
Artic Charr
Salvelinus alpinus
Planktivorous feeder
Annual growth variation
Population Age-Size structure
Population Size-Age relationship
Age measurement methods
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Scales
Otoliths
Vertebrae
Rays/Spines
Age measurement through scales
Age measurement through otoliths
Otolith uses
• Age determination
– Daily ring counts
– Annual ring counts
– Radioactive isotopes
• Species identification
• Paleoclimate studies (018)
• Life history studies (elemental
tracers)
(Oncorhynchus clarkii)
Weakfish (Cynoscion regalis)
Otolith age validation
Otolith age validation
Otolith age validation – nuclear fallout
Age calculation error case
Anoplomatidae
Sablefish
Anoplopoma fimbria
Scales: 3-8 years
Otoliths: 4-40 & up to 80
Species identification
Dolphin stomach contents
Climate studies (isotope 018)
Climate studies (isotope 018)
(6000 year old fossil)
Elemental tracers – Life history
(Zn, Sr, Ba, Mn, Fe and Pb)
Elemental tracers
of weakfish
Thorrold et al. 2001
Proof of Natal Homing!
Thorrold et al. 2001
How many fish are there?
How do populations change?
Nt+1 = Nt + B – D + I – E
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B = births
D = deaths
I = immigration
E = emigration
Immigration
Stocking
Births
Deaths
Population
Angling
Emigration
Survival
• Eggs and larvae suffer the largest
losses
HATCH
Egg
Larva Viable & Competent
Not Fertile
Starvation
Inviable
Eaten
Eaten
Other
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
Recruit!
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
What determines recruitment?
-Stock size (number and size of females)
Density-independent
Ricker
What determines recruitment?
Beverton-Holt
spawning stock biomass (SSB)
From: Wootton (1998). Ecology of teleost fishes.
Density-independent
Ricker
What determines recruitment?
Beverton-Holt
spawning stock biomass (SSB)
From: Wootton (1998). Ecology of teleost fishes.
Density-independent
Ricker
What determines recruitment?
Beverton-Holt
spawning stock biomass (SSB)
From: Wootton (1998). Ecology of teleost fishes.
The problem?
• Stochasticity = variable recruitment!
From: Cushing (1996). Towards
a science of recruitment in fish
populations
Highly variable recruitment results
in naturally very variable catches
From: Jennings, Kaiser and Reynolds (2001). Marine Fisheries Ecology
Population Abundance
• On rare occasions, abundance can be
measured directly
– Small enclosed systems
– Migration
Catch per unit effort (CPUE)
• Very coarse and very common index
of abundance
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
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 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
Number Caught
Closed population
Vulnerability constant for each p
Collection efficiency constant
Often not simple linear regressio
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Number previously caught
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
M=5
N=population size=????
C=4
R=2
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
• Closed population
• Equal catchabilty in first sample
• Marking does NOT influence
catchability
• Multiple recaptures
– Easier to pick up on violation of assumptions