1. Biodiversity of Fishes Population Growth and Exploitation
Rainer Froese

2. Thomas Robert Malthus (1766 – 1834, English Economist)

3. World Population Growth
"The power of population is indefinitely greater than the power in the earth to produce subsistence for man"

4. Pierre François Verhulst (1804 – 1849, Belgian Mathematician)
(1844)

5. BioDivPopGrowthMSY.xls

6. Logistic Curve Properties
BioDivPopGrowthMSY.xls

7. Milner Baily Schaefer (1912 – 1970, US Fisheries Scientist)

8. The Schaefer Model
BioDivPopGrowthMSY.xls

9. Surplus Production Implications
Surplus production (Y) is the production of biomass beyond what is needed to maintain current population size
If a fishery only catches the surplus production, then the population size remains
If a fishery catches more, then the population shrinks
If it catches less, then the population grows

10. Surplus Production Implications
Surplus production has a maximum at about half of unexploited population size B∞
Keeping a population at 0.5 B∞ allows catching MSY forever
A population is kept stable if the fishing rate F equals the intrinsic growth rate rt
MSY is reached at ½ B∞ and ½ rmax
Thus, MSY is reached at Fmsy = ½ rmax

11. The Law of the Sea
The Law of the Sea (UNCLOS 1982) requires all signatories to maintain fish stocks at levels that can produce the maximum sustainable yield MSY
The EU Common Fisheries Policy has implemented the MSY provision in 2014
Thus, the fishing rate F may not exceed Fmsy in European fisheries management

12. Outside safe biological limits
The MSY Framework
High biomass
High profit
High catch
Overfishing
CFP 2013
Recovering
Outside safe biological limits

13. Status and Exploitation of European Stocks
Presentation of 397 stocks in European Seas in a pressure (F/Fmsy) – state (B/Bmsy) plot. The
red area indicates stocks that are being overfished or are outside of safe biological limits.
The yellow area indicates recovering stocks. The green area indicates stocks subject to
sustainable fishing pressure and of a healthy stock size that can produce high yields close to MSY.

14. Exploitation of 397 stocks in European Seas in 2013-2015
Exploitation of 397 stocks in European Seas in Note overlapping of different types of overexploitation, and therefore the numbers do not add up to 100% Froese et al. 2016

15. Status of 397 stocks in European Seas. Froese et al. 2016

16. Analysis of current (2013 -2015) and potential catches for 397 stocks in European Seas. Because
of trophic interactions, all stocks cannot support maximum yields simultaneously.

17. Status and Exploitation of European Stocks
Froese et al. 2016

18. Conclusions
The Common Fisheries Policy sets the correct goal of rebuilding stocks above levels that can produce MSY
An analysis of all European stocks shows that the goal of sustainable exploitation by 2015 has been missed by a large margin
Therefore, there is no visible trend of rebuilding in European fish stocks
However, sustainable catches can be 5 MT (57%) higher if stocks have been rebuilt

19. Why is Management so Bad?
Depending on the productivity of the species (rmax), about 20% of the biomass can be taken sustainably every year
Therefore, about 80% of the fish have to be left in the water, although they are easily accessible
There is only one problem

20. GREED

21. “Heringszaun”, Kappeln, Germany
Fish weirs in rivers typically cover % of the river width, facing toward the sea,
so they catch the fish before they can spawn. And there used to be many of these.

22. Exercise
Go to select Community, Advisory Process, Latest Advice
Search for a stock for which ICES gives Fmsy
Use graphs to discuss trends in biomass and catch as a function of F / Fmsy
What happens if F > rmax?
[show example: mackerel]