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The science behind minimum landing sizes and minimum conservation reference sizes
Ken H. Andersen
The science behind minimum landing sizes and minimum conservation - - PowerPoint PPT Presentation
The science behind minimum landing sizes and minimum conservation - - PowerPoint PPT Presentation
The science behind minimum landing sizes and minimum conservation reference sizes Ken H. Andersen How? Single species perspective Abundance R log( w ) w0 W R p BH Recruitment Single-species simulation
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… w0 W log(w)
R BH Recruitment Rp
Single species perspective
Abundance
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Single-species simulation
Fishing mortality Biomass http://stockassessment.org/spectrum
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Maximum sustainable yield
Length at 50% retainment “mesh size” Fishing mortality size at maturation
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Differences between stocks
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Why?
size at maturation weight age W∞ Mortality weight
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Controversy
Science, 2012
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Optimal yield
Mesh size (g) Fishing mortality (yr-1) 10 10
1
10
2
10
3
0.2 0.4 0.6 0.8 1
Catch largefish Beverton-Holt standard theory
Mesh size (g) Fishing mortality (yr-1) 10 10
1
10
2
10
3
0.2 0.4 0.6 0.8 1
Catch small fish Fisheries yield Low stock size High stock size
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Early life density dependent control Density dependent growth Classic Beverton-Holt theory
?
Mesh size (g) Fishing mortality (yr-1) 10 10
1
10
2
10
3
0.2 0.4 0.6 0.8 1 Mesh size (g) Fishing mortality (yr-1) 10 10
1
10
2
10
3
0.2 0.4 0.6 0.8 1
Yield
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Beyond state of the art
0.5 0.6 0.7 0.8 0.9 1.0 0.5 0.6 0.7 0.8 0.9 1.0 0.5 0.6 0.7 0.8 0.9 1.0 6 9 12 20 30 40 20 30 40 50 Fishery size−at−entry (cm) Relative highest yield Relative highest yield Relative highest yield
By: Rob van Gemert
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Fisheries reference points
𝑋
∞ = 333 g
𝑋
∞ = 10 g
𝑋
∞ = 10 kg
Yield Biomass Fishing mortality
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How do we characterize fish?
Size
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… w0 W log(w)
R BH Recruitment Rp
Single species perspective
Abundance
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Single-species simulation
Fishing mortality Biomass http://stockassessment.org/spectrum
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Fcrash Fmsy Flim Asymptotic weight (g) Andersen and Beyer (2015) F&F
Fisheries reference points
Fishing mortality
0.00 0.25 0.50 0.75 10 100 1000 10000 1e+05
W¥ FMSY
“Metabolic” scaling, Fmsy W-1/4