Age Structure
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Age Structure
description
Age Structure. Learning Objectives. Understand the uses of an age-length key Calculate age structure using an age-length key Identify uses of age structure data and common pitfalls. Age Structure. Age Structure. Subsampling. Subsampling. Subsampling. Is this correct?. Age-Length Key. - PowerPoint PPT Presentation
Transcript of Age Structure
Age Structure
Learning Objectives
• Understand the uses of an age-length key• Calculate age structure using an age-length
key• Identify uses of age structure data and
common pitfalls
Age Structure
Age Structure
Subsampling
Subsampling
Subsampling
Length group (mm)
0 100 200 300 400 500
Num
ber
0
2
4
6
8
10
12n = 333
Length group (mm)
0 100 200 300 400 500
Num
ber
0
50
100
150
200
250
300n = 2,242
Is this correct?
Age (yrs)
0 1 2 3
Rel
ativ
e fr
eque
ncy
(%)
0
10
20
30
40
50
60n = 333
Age-Length Key
Age (yrs)
0 1 2 3
Rel
ativ
e fr
eque
ncy
(%)
0
10
20
30
40
50
60
70
n = 2,242
Age (yrs)
0 1 2 3
Rel
ativ
e fr
eque
ncy
(%)
0
10
20
30
40
50
60
Age (yrs)
0 1 2 3
Rel
ativ
e fr
eque
ncy
(%)
0
10
20
30
40
50
60
70
n = 333
n = 2,242
Which one do you think is most accurate?
Subsample only
From ALK
Age-Length Key
• Mean length-at-age
Li = ΣNij lij (Ni)-1
Si2 = [ΣNij (lij-Li)2] (Ni –1)-1
where, Li = mean length of the ith age group, Si2 = variance in
mean length of the ith age group, Nij = Nj (nij/nj), Nj = total number of fish in the jth length group, nij = number of fish of the ith age group subsampled from the jth length group, nj = number of fish subsampled in the jth length group, lij is the mean length of fish of the ith age group subsampled from the jth length group, and Ni = ΣNij over all j length groups.
Age-Length Key
Age-Length Key
This is simply a weighted mean:
Li = (ΣNij × lij) / Ni = 10,447 / 141 = 74 mm
Ni = ΣNij
If we only use the subsample, mean length is 77 mm
Age-Length Key
Si2 = [ΣNij (lij – Li)2] lij) / (Ni – 1) = 41,559 / 140 = 297
Age-Length Key
