Transcript PPT - FishBase

Status of European Stocks
Rainer Froese, GEOMAR, Kiel
WKGMSFDD3-II
Copenhagen, 10-12 February 2015
Bayesian State-Space Production Model
ICES_Results.xlsx, Froese et al. submitted
2013 Status of 47 Stocks
CFP
Naming the Stocks
Froese et al. submitted
Summary for Stock Status
• The CFP law sets stock status levels that are
scientifically, ecologically and economically
sound and standard in USA, Australia, NZ, …
• MSFD is a directive that has to follow the
binding CFP law
• Bmsy can be easily estimated for all ICES
stocks with catch and biomass or CPUE data,
no need for Bpa or MSY_Btrigger (5%
probability of producing MSY) as proxies
• Many stocks (19%) already fulfil B > Bmsy
Size Structure and Selectivity
• What is the age and size structure that allows a
population to reproduce and fulfil its ecosystem
role as prey or predator?
• The natural length at first maturity is about 1/3 to
½ of maximum length
• The natural average length of parents is about
2/3 of maximum length
• Starting fishing at about ½ of maximum length
allows all fish to reproduce and leads to natural
average length; it also maximizes catch and
biomass for a given F (Froese et al. in prep.)
Yield-per-Recruit
Yield per recruit is a function of F and Lc (Beverton & Holt 1957).
The Equation for Optimum Selectivity
𝐿𝑐_𝑜𝑝𝑡
𝐾(3𝐹 + 2𝑀)
= 𝐿∞
(𝐹 + 𝑀)(3𝐾 + 𝑀)
Lc_opt maximizes catch and biomass
Lc_opt minimizes impact on size & age structure
For F <= M, Lc_opt is about half of maximum length
Froese et al. in prep.
Optimizing Selectivity
For every F, there is a corresponding length-at-first-capture (Lc) that maximizes catch (dashed
Lc_max curve) or that maximizes catch and increases biomass (solid Lc_opt curve, Froese et al.,
in prep.)
Optimizing Biomass
Does Not Reduce Catch
For a given F, starting fishing at Lc_opt gives the same yield as starting fishing at Lc_max
Yield-per-Recruit Analysis
In the area of reasonable fishing, yield lines are nearly parallel to the length-at-first-capture axis.
Using Yield-per-Recruit Analysis
For a given F, starting fishing at Lc_opt gives higher biomass than starting at Lc_max
Biomass as a Function of F/M and
Length at first Capture
Froese et al. in prep.
Long-term Catch as a Function of F/M
and Length at First Capture
Froese et al. in prep.
Healthy Age & Size Structure I
Froese et al. in prep.
Healthy Age & Size Structure II
Froese et al. in prep.
Summary
• Setting selectivity (length at first capture Lc)
right will increase catches, biomass, and age
structure
• Lm50 should be a lower limit reference point
for Lc
• Lc_opt or half of Linf is a good target reference
point for Lc
Thank You