age and growth growth & age patterns measurement techniques
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Age and Growth
Growth & age patternsMeasurement techniques
Growth patterns• Determinate Growth
– Mammals & birds
• Indeterminate Growth– Fishes
Determinate
Indeterminate
Age
Siz
e
Indeterminate growth & fecundity
Fish growth – von Bertalanffy equationLt=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
• Temperature• Food and Nutrient Availability• Light Regime• Oxygen Concentration• Salinity• Pollutants• Predator Densities• Intraspecific Social Interactions• Genetics
Example: Species polymorphism
SalmonidaeArtic CharrSalvelinus alpinus
Large benthic feeder
Small benthic feeder
Piscivorous feeder
Planktivorous feeder
Annual growth variation
Population Age-Size structure
Population Size-Age relationship
Age measurement methods
• 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 – nuclear fallout
AnoplomatidaeSablefishAnoplopoma fimbria
Age calculation error case
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)
Thorrold et al. 2001
Elemental tracersof weakfish
Proof of Natal Homing!
Thorrold et al. 2001
How many fish are there?
Nt+1 = Nt + B – D + I – E
B = births D = deaths I = immigration E = emigration
How do populations change?
DeathsPopulationBirths
Emigration
Immigration
Stocking
Angling
Survival• Eggs and larvae suffer the largest
losses
Egg
Not Fertile
Inviable
Eaten
Other
Larva Viable & Competent
Starvation
Eaten
HATCHRecruit!
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• 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)
What determines recruitment?
spawning stock biomass (SSB)
Ricker
Beverton-Holt
Density-independent
From: Wootton (1998). Ecology of teleost fishes.
What determines recruitment?
spawning stock biomass (SSB)
Ricker
Beverton-Holt
Density-independent
From: Wootton (1998). Ecology of teleost fishes.
What determines recruitment?
spawning stock biomass (SSB)
Ricker
Beverton-Holt
Density-independent
From: Wootton (1998). Ecology of teleost fishes.
The problem?
• Stochasticity = variable recruitment!
From: Cushing (1996). Towards a science of recruitment in fishpopulations
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
Effort= 4 nets for 12 hours each= 48 net hours
Catch= 4 fish
CPUE=4/48=0.083
Effort= 4 nets for 12 hours each= 48 net hours
Catch=8 fish
CPUE=8/48=0.167
We conclude population 2 is 2X larger than population 1
1
2
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
*
*
*
*
Num
ber
Cau
ght
Number previously caught
Closed populationVulnerability constant for each passCollection efficiency constantOften not simple linear regression
Estimates of Population Size
• Mark & Recapturecapture – 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 C=4 R=2
N=population size=????
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