1. Size Structure

2. Learning Objectives Construct and interpret length-frequency distributions Describe, calculate, and interpret Swingle’s ratios Describe the development and interpretation of standardized length categories Calculate and interpret PSS indices Describe differences associated with using traditional and incremental size-structure indices Identify the dynamic rate functions and relations with size structure indices

3. Size Structure Methods of measurement of fish population structure Calculation of indices Interpretation of structural indices

4. Fish Length and Weight

5. Considerations

6. Indices

7. Homer Swingle Faculty member at Auburn University One of the first to use experimental ponds to obtain insight on management Interested in “balanced” fish populations in ponds

8. Balance “The interrelationships in fish populations are satisfactory if the populations yield, year after year, crops of harvestable fish that are satisfactory in amount when the basic fertilities of the bodies of water containing those populations are considered. Such populations are considered to be ‘balanced populations’ and the species within such a population are ‘in balance.’” “Balance then denotes a condition within a population such that if 100 pounds of fish are harvested one year the correct numbers of replacements will be provided from the population so that a satisfactory poundage of fish of desirable size may be harvested in succeeding years. If the population provides too many replacements, these fish will not reach a satisfactory size for harvesting; conversely, if too few replacements are provided, the capacity of the body of water to produce will not be fully utilized and the harvestable poundage will seriously decline.”

9. Swingle’s F/C Ratio

10. F = C =

11. Swingle’s F/C Ratio

13. Swingle’s Y/C Ratio Y = C =

14. Swingle’s Y/C Ratio

16. Swingle’s A t

17. SpeciesMinimum weight BLG, RESF, and similar sunfishes 0.1 Crappies0.26 LMB0.4 Bullheads0.3 GZS0.5 CHCF0.5 Gar1.0 Buffalo1.0 Carp1.0

18. Swingle’s A t

22. Swingle’s E Swingle’s E = Lower bound of balanced with 1 “C” and 1 “F” species is 1.4:1 (BLG:LMB). Therefore, there is 1 pound of LMB for every 2.4 lbs of fish (100 × 1 / 2.4 = 41.6%) –LMB (balanced) = –LMB (desired)=

23. Other Swingle Indices A value = I value = S value =

24. Jenkins and Morais Metric AP/P ratio –AP = –P = –Plotted on a log 10 vs log 10 scale –Curve should be above the 1:1 line to have sufficient prey for predators

25. Jenkins and Morais Metric

26. Swingle Ratios and Similar Indices Potential problems and practicality???

27. Length-Frequency Histograms

28. Guidelines ROT…sample 100 fish > stock-length

29. Guidelines Y-axis

30. Guidelines X-axis are bins “bin bias”

31. Bin Bias

32. Length-Frequency Indices

33. Length Categorization Weithman and Anderson (1978) Gabelhouse (1984)

34. Length Categorization Stock length = Quality length = Preferred length = Memorable length = Trophy length =

35. Length Categorization

36. Proportional Stock Density (PSD) Proportion of stock-length fish that are quality length or greater PSD = 100 × (# of fish > minimum quality length / # of fish > minimum stock length) Round to nearest whole number!

37. PSD-WAE Example

39. PSD SQ S = 29 Q = 17 S = 29 Q = 17

40. RSDs RSD = 100 × (# of fish > specified length / # of fish > stock length) Round to nearest whole number! Specified length (e.g., RSD-35) Standard length categories

41. RSD-WAE Example Substock (< 250 mm) = 7 Stock (250 mm) = 29 Quality (380 mm) = 17 Preferred (510 mm) = 10 Memorable (630 mm) = 6 Trophy (760 mm) = 0

42. SQ PSD = 59 RSD-P = RSD-M = RSD-370 = PSD = 59 RSD-P = RSD-M = RSD-370 = PMT

43. Traditional versus Incremental RSDs Traditional RSDs Incremental

44. RSD-WAE Example S QPMT

45. SS = S-Q = Q-P = P-M = M-T = T =

46. RSD-WAE Example S QPMT SQ QPPMMTTSS

47. Traditional versus Incremental RSDs Incremental RSDs Traditional RSDs

48. Proportional Size Structure (PSS) Confusion in terminology with Proportional Stock Density and Relative Stock Density

49. Proportional Size Structure CurrentNew PSDPSS Q RSD-QPSS Q RSD-PPSS P RSD-MPSS M RSD-TPSS T RSD S-QPSS SQ RSD Q-PPSS QP RSD P-MPSS PM RSD M-TPSS MT Terminology

50. Size Structure

53. Biases

56. Balance Balanced populations have predictable PSD (or PSS Q ) Examples –BLG –Crappie –LMB

57. Balance A T, but with biomas s

58. Additional insight

59. Size Structure Indices

62. “The Classic Story of BLG and LMB PSDs”

75. What about other species?