1. Mark Recapture lecture 1
An example from Sockeye salmon….

5. Mark recapture lectures
Petersen method
Schnabel method
Schumacher-Eschmeyer
Jolly Seber
Closed population
Open population
Overview of methods to help your reading of Krebs Chp 2

6. Closed populations
No individuals enter or leave the population between surveys
Survey 1
Survey 2

7. Individuals enter or leave the population between surveys
Open populations
Individuals enter or leave the population between surveys
Survey 1
Survey 2

8. What makes a population closed?
Dispersal barriers
Philopatry
Large surveyed area
Slow reproductive/death rate
Short time between surveys

9. What type of population are snow geese?

10. Snow Goose
La Pérouse Bay

11. Recording which birds are marked, and marking new birds

12. LPB Colony size
Year

13. Petersen method: Closed population
Survey 1:
Survey 2:
Catch several animals
Catch C animals
Count recaptures (R)
Mark all M animals
Return animals to population
Return animals to population

14. Survey 2:
C = 15
R = 4
Survey 1:
M = 12

15. What is the total population size (N)?
Note that the proportion marked in the population
equals the proportion marked in the 2nd sample
M = R
N C
N = M C R
M = 12
C = 15
R = 4

16. What is the total population size (N)?
Note that the proportion marked in the population
equals the proportion marked in the 2nd sample
N = 13 * 16 5 -1
N = (M+1) (C+1)
(R+1) -1
M = 12
C = 15
R = 4

17. When would Petersen give you a bad estimate?
Population not closed
Marked animals likely to be re-trapped
Marked animals likely to die
Marks fall off

18. Schnabel method: closed population
Survey 1
Survey 2
Survey 3
Survey 4
Survey 5
Essentially, Petersen estimates on multiple surveys

19. Schnabel method: closed population
Catch Ct animals
Survey t:
Mark Ut unmarked animals
Return animals to population
Record Rt recaptures

20. Schnabel method: closed population
Survey t:
Catch Ct animals
What’s the relationship between Ct, Rt, and Ut ?
Record Rt recaptures
Mark Ut unmarked animals
Ct = Rt + Ut
Return animals to population

21. Schnabel method: example
Time (t) Ct Rt Ut 1 20 2 5 3 13 4 10
How many individuals marked by beginning of time 5?

22. Schnabel method: example
Time (t) Ct Rt Ut 1 20 2 5 15 3 7 13 4 10
How many individuals marked by beginning of time 5?

23. Schnabel method: example
Time (t) Ct Rt Ut 1 20 2 5 15 3 7 13 4 10
Σ = 58

24. Schnabel method: example
Time (t) Ct Rt Ut 1 20 2 5 15 3 7 13 4 10
In general: Mt = U1 + U2..Ut-1
Σ = 58

25. Schnabel formulas: N = Σ (Ct Mt) Σ Rt N = Σ (Ct Mt) Σ Rt+1
Marked > 10% of population
N = Σ (Ct Mt)
Σ Rt+1
Marked < 10% of population
( just weighted average of Petersen estimates!)

26. Schnabel method: example
Time (t) Ct Rt Ut Mt
CtMt 1 20 2 5 15 3 7 13 35 4 10 48

27. Schnabel method: example
Time (t) Ct Rt Ut Mt
CtMt 1 20 2 5 15
400 3 7 13 35
700 4 10
960 48
Σ = 22
Σ = 2060

28. Schnabel method: example
Time (t) Ct Rt Ut Mt
CtMt 1 20 2 5 15
400 3 7 13 35
700 4 10
960
N = Σ (Ct Mt) = 2060 = 94
Σ Rt 48
Σ = 22
Σ = 2060

29. Schnabel method: example
Time (t) Ct Rt Ut Mt
CtMt 1 20 2 5 15
400 3 7 13 35
700 4 10
960
What proportion of total population marked by end? 48
Σ = 22
Σ = 2060

30. Scumacher-Eschmeyer method (for Schnabel experiment)
N = C M R
R = 1 * M
C N
y = mx + b

31. Scumacher-Eschmeyer method (for Schnabel experiment)
N = C M R
R = 1 * M
C N R C
Slope = ? M