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Age and Growth

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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Age and Growth

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  1. Age and Growth Growth & age patterns Measurement techniques

  2. Indeterminate Determinate Size Age Growth patterns • Determinate Growth • Mammals & birds • Indeterminate Growth • Fishes

  3. Indeterminate growth & fecundity

  4. Fish growth – von Bertalanffy equation Lt=Lmax(1-e-kt)

  5. Fish growth – von Bertalanffy equation

  6. Length – Weight relation (power function) W=a Lb

  7. Growth patterns • Great Plasticity in growth • Size at age: High variability • Between species • Between populations • Between individuals

  8. Environmental factors influencing growth • Temperature • Food and Nutrient Availability • Light Regime • Oxygen Concentration • Salinity • Pollutants • Predator Densities • Intraspecific Social Interactions • Genetics

  9. Example: Species polymorphism Large benthic feeder Small benthic feeder Piscivorous feeder Salmonidae Artic Charr Salvelinus alpinus Planktivorous feeder

  10. Annual growth variation

  11. Population Age-Size structure

  12. Population Size-Age relationship

  13. Age measurement methods • Scales • Otoliths • Vertebrae • Rays/Spines

  14. Age measurement through scales

  15. Age measurement through otoliths

  16. Otolith uses • Age determination • Daily ring counts • Annual ring counts • Radioactive isotopes • Species identification • Paleoclimate studies (018) • Life history studies (elemental tracers)

  17. (Oncorhynchus clarkii)

  18. Weakfish (Cynoscion regalis)

  19. Otolith age validation

  20. Otolith age validation

  21. Otolith age validation – nuclear fallout

  22. Age calculation error case Scales: 3-8 years Otoliths: 4-40 & up to 80 Anoplomatidae Sablefish Anoplopoma fimbria

  23. Species identification

  24. Dolphin stomach contents

  25. Climate studies (isotope 018)

  26. Climate studies (isotope 018) (6000 year old fossil)

  27. Elemental tracers – Life history(Zn, Sr, Ba, Mn, Fe and Pb)

  28. Elemental tracers of weakfish Thorrold et al. 2001

  29. Proof of Natal Homing! Thorrold et al. 2001

  30. How many fish are there?

  31. 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

  32. 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

  33. 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

  34. What determines recruitment? -Stock size (number and size of females)

  35. spawning stock biomass (SSB) Density-independent Ricker What determines recruitment? Beverton-Holt From: Wootton (1998). Ecology of teleost fishes.

  36. spawning stock biomass (SSB) Density-independent Ricker What determines recruitment? Beverton-Holt From: Wootton (1998). Ecology of teleost fishes.

  37. spawning stock biomass (SSB) Density-independent Ricker What determines recruitment? Beverton-Holt From: Wootton (1998). Ecology of teleost fishes.

  38. The problem? Stochasticity = variable recruitment!

  39. From: Cushing (1996). Towards a science of recruitment in fish populations

  40. Highly variable recruitment results in naturally very variable catches From: Jennings, Kaiser and Reynolds (2001). Marine Fisheries Ecology

  41. Population Abundance On rare occasions, abundance can be measured directly Small enclosed systems Migration

  42. 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

  43. 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

  44. 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

  45. Depletion methods Closed population Vulnerability constant for each pass Collection efficiency constant Often not simple linear regression * * Number Caught * * Number previously caught

  46. 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

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