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 http://stockassessment.org/spectrum Fishing mortality Biomass

Maximum sustainable yield Fishing mortality size at maturation Length at 50% retainment “mesh size”

Differences between stocks

W∞ weight age Why? size at maturation Mortality weight

Controversy Science, 2012

Optimal yield Fisheries yield 1 Fishing mortality (yr -1 ) 0.8 0.6 0.4 Low stock size 0.2 0 High stock size 0 1 2 3 10 10 10 10 Mesh size (g) Catch small fish Catch largefish 1 Fishing mortality (yr -1 ) 0.8 0.6 0.4 Beverton-Holt standard theory 0.2 0 0 1 2 3 10 10 10 10 Mesh size (g)

Yield 1 Fishing mortality (yr -1 ) Density dependent growth 0.8 0.6 0.4 0.2 0 0 1 2 3 10 10 10 10 Mesh size (g) ? 1 Fishing mortality (yr -1 ) 0.8 Classic Beverton-Holt theory 0.6 Early life density dependent control 0.4 0.2 0 0 1 2 3 10 10 10 10 Mesh size (g)

Beyond state of the art 1.0 Relative highest yield 0.9 0.8 0.7 0.6 0.5 6 9 12 1.0 Relative highest yield 0.9 0.8 0.7 0.6 0.5 20 30 40 1.0 Relative highest yield 0.9 0.8 0.7 0.6 0.5 By: Rob van Gemert 20 30 40 50 Fishery size − at − entry (cm)

Fisheries reference points Yield 𝑋 ∞ = 333 g Biomass Fishing mortality 𝑋 ∞ = 10 g 𝑋 ∞ = 10 kg

How do we characterize fish? Size

Single species perspective … Abundance R log( w ) w0 W  R p BH Recruitment

Single-species simulation http://stockassessment.org/spectrum Fishing mortality Biomass

Fisheries reference points 0.75 0.50 F MSY Fishing mortality 0.25 Fcrash Flim 0.00 10 100 1000 10000 1e+05 W ¥ “Metabolic” scaling, F msy W -1/4 Fmsy Asymptotic weight (g) Andersen and Beyer (2015) F&F