1 / 65

Population Dynamics

Population Dynamics. Mortality, Growth, and More. Fish Growth. Growth of fish is indeterminate Affected by: Food abundance Weather Competition Other factors too numerous to mention!. Fish Growth. Growth measured in length or weight Length changes are easier to model

lucio
Download Presentation

Population Dynamics

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript


  1. Population Dynamics Mortality, Growth, and More

  2. Fish Growth • Growth of fish is indeterminate • Affected by: • Food abundance • Weather • Competition • Other factors too numerous to mention!

  3. Fish Growth • Growth measured in length or weight • Length changes are easier to model • Weight changes are more important for biomass reasons

  4. Growth rates - 3 basic types • Absolute - change per unit time - l2-l1 • Relative - proportional change per unit time - (l2-l1)/l1 • Instantaneous - point estimate of change per unit time - logel2-logel1

  5. Growth in length

  6. Growth in length & weight

  7. von Bertalanffy growth model

  8. Von Bertalanffy growth model

  9. Ford-Walford Plot

  10. More calculations For Lake Winona bluegill: K = 0.327 L∞ = 7.217 inches Predicting length of 5-year-old bluegill:

  11. Weight works, too! b often is near 3.0

  12. Exponential growth model Over short time periods Gives best results with weight data, does not work well with lengths Initial weight Weight at time t Instantaneous growth rate Used to compare different age classes within a population, or the same age fish among different populations

  13. Fish Mortality Rates • Sources of mortality • Natural mortality • Predation • Diseases • Weather • Fishing mortality (harvest) Natural mortality + Fishing mortality = Total mortality

  14. Fish Mortality Rates • Lifespan of exploited fish (recruitment phase) • Pre-recruitment phase - natural mortality only • Post-recruitment phase - fishing + natural mortality

  15. Estimating fish mortality rates • Assumptions 1) year-to-year production constant 2) equal survival among all age groups 3) year-to-year survival constant • Stable population with stable age structure

  16. Estimating fish mortality rates • Number of fish of a given cohort declines at a rate proportional to the number of fish alive at any particular point in time • Constant proportion (Z) of the population (N) dies per unit time (t)

  17. Estimating fish mortality rates Number alive at time t Number alive initially - at time 0 Instantaneous total mortality rate Time since time0

  18. Estimating fish mortality rates If t = 1 year S = probability that a fish survives one year 1 - S = AA = annual mortality rate or

  19. Recalling survivorship

  20. Recalling survivorship

  21. Mortality rates: catch data • Mortality rates can be estimated from catch data • Linear least-squares regression method • Need at least 3 age groups vulnerable to collecting gear • Need >5 fish in each age group

  22. Mortality rates: catch data 2nd edition p. 144

  23. Calculations Start with: Take natural log of both sides: Takes form of linear regression equation: Slope = -z Y intercept

  24. slope Slope = -0.54 = -z z = 0.54

  25. Annual survival, mortality S = e-z = e-0.54 = 0.58 = annual survival rate 58% chance of a fish surviving one year Annual mortality rate = A = 1-S = 1-0.58 = 0.42 42% chance of a fish dying during year

  26. Robson and Chapman Method - survival estimate Total number of fish in sample (beginning with first fully vulnerable age group) Sum of coded age multiplied by frequency

  27. Same data as previous example, except for age 1 fish (not fully vulnerable) Example 350 total fish

  28. Example T = 0(150) + 1(95) + 2(53) + 3(35) + 4(17) = 374 52% annual survival Annual mortality rate A = 1-S = 0.48 48% annual mortality

  29. Variability estimates • Both methods have ability to estimate variability • Regression (95% CI of slope) • Robson & Chapman

  30. Brown trout Gilmore Creek - Wildwood 1989-2010

  31. Separating natural and fishing mortality • Usual approach - first estimate total and fishing mortality, then estimate natural mortality as difference • Total mortality - population estimate before and after some time period • Fishing mortality - angler harvest

  32. Separating natural and fishing mortality z = F + M z = total instantaneous mortality rate F = instantaneous rate of fishing mortality M = instantaneous rate of natural mortality

  33. Separating natural and fishing mortality Also: A = u + v A = annual mortality rate (total) u = rate of exploitation (death via fishing) v = natural mortality rate

  34. Separating natural and fishing mortality May also estimate instantaneous fishing mortality (F) from data on fishing effort (f) F = qf q = catchability coefficient Since Z = M + F, then Z = M + qf (form of linear equation Y = a + bX) (q = slope M = Y intercept) Need several years of data: Annual estimates of z (total mortality rate) Annual estimates of fishing effort (angler hours, nets)

  35. Separating natural and fishing mortality Once relationship is known, only need fishing effort data to determine z and F Total mortality rate (z) Mortality due to fishing M = total mortality when f = 0 Amount of fishing effort (f)

  36. Abundance estimates Necessary for most management practices Often requires too much effort, expense Instead, catch can be related to effort to derive an estimate of relative abundance

  37. Abundance estimates • C/f = CPUE • C = catch • f = effort • CPUE = catch per unit effort • Requires standardized effort • Gear type (electrofishing, gill or trap nets, trawls) • Habitat type (e.g., shorelines, certain depth) • Seasonal conditions (spring, summer, fall)

  38. Abundance estimates • Often correlated with actual population estimates to allow prediction of population size from CPUE Population estimate CPUE

  39. Population structure • Length-frequency distributions • Proportional stock density

  40. Proportional stock density • Index of population balance derived from length-frequency distributions

  41. Proportional stock density • Minimum stock length = 20-26% of angling world record length • Minimum quality length = 36-41% of angling world record length

  42. Proportional stock density • Populations of most game species in systems supporting good, sustainable harvests have PSDs between 30 and 60 • Indicative of a balanced age structure

More Related