1. MSFD Indicators and Reference Points for Data-Limited Stocks
Rainer Froese
GEOMAR
EU-BON Workshop, Leipzig
18 February 2014

2. Some Terms
Maximum sustainable yield (MSY) is the maximum surplus production in numbers or weight (= ecosystem service) that an exploited population can provide forever
Biomass (B) is the size of a population in weight
Bmsy is the biomass that can produce MSY
Fmsy is the anthropogenic mortality rate that will result eventually in Bmsy

3. MSFD Descriptor 3
The level of pressure of the fishing activity, measured either as fishing mortality F relative to the one associated with the maximum sustainable yield (Fmsy) or, if F is unknown, the ratio between catch and biomass, with a reference point that is compatible with Fmsy.
The spawning stock biomass SSB relative to the one that can produce the maximum sustainable yield (SSBmsy) or other suitable biomass indices.
The age and size distribution within the population, with the sub-indicators
Proportion of fish larger than the mean size of first sexual maturation;
Mean maximum length across all species found in research vessel surveys;
95 % percentile of the fish length distribution observed in research vessel surveys;
Size at first sexual maturation [relative to historic sizes], which may reflect the extent of undesirable genetic effects of exploitation.

4. What is a Proxy for Fmsy?
Fmsy is the maximum mortality that may be inflicted by humans
Fmsy is known for less than ¼ of exploited fish stocks
Natural mortality M can be used as a proxy for Fmsy

5. M as Proxy for Unknown Fmsy
A fishing mortality rate F that equals the natural mortality rate M effectively
doubles the mortality rate that the species has evolved to withstand
reduces life expectancy and duration of reproductive phase by half
reduces the number of old, large, fecund fish

6. M as Proxy for Unknown Fmsy
There is a broad, longstanding agreement in fisheries science that sustainable rates of fishing F may not exceed Fmsy and shall not exceed M.
Gulland 1971, Shepherd 1981, Beddington and Cooke 1983, Clark et al. 1985, Beverton 1990, Patterson 1992, Thompson 1993, Walters and Martell 2002, 2004, MacCall 2009, Pikitch et al
Thus, M can be used as a proxy for Fmsy

7. What is a Proxy for Bmsy
Bmsy is the internationally agreed minimum size of exploited marine populations (UNCLOS 1982)
However, there are no agreed estimates of Bmsy for European stocks
A proxy for Bmsy can be derived from the biomass representing borderline of safe biological limits, which is available for many stocks

8. 2 * Bpa as Proxy for Unknown Bmsy
Over the past two decades the border to safe biological limits Bpa was used as reference point in European fisheries
In fisheries textbooks, half of Bmsy is typically assumed as the borderline to unsafe stock status.
It follows that 2*Bpa is a reasonable proxy for Bmsy

9. DATRAS: Millions of Survey Records http://datras.ices.dk

10. SMALK: Length-Weight Needed to turn length into weight and biomass
North Sea flounder: 25,609 observations of length and weight; 42 outliers were removed.
Weight = * Length [SMALK_Analysis_25.r]

11. SMALK: Growth Needed to turn length into age
North Sea flounder: 25,501 observations of length and age.
Length-at-age = 48 * (1 – e-0.11 * (age – 2.8)) [SMALK_Analysis_25.r]

12. SMALK: Length & Age at Maturity Needed for proxy recruits and spawners
North Sea flounder: 10,814 observations of length, age, and state of maturity.
Female length where 90% are mature is 23 cm, age is 2-3 years [SMALK_Analysis_25.r]

13. CPUE in Area 6
Average catch in numbers of North Sea cod resulting from one hour of trawling with
standardized survey gears. The bold line represents a three-year moving average to
reduce scatter and facilitate interpretation of trends. The dotted line indicates the mean
catch of the time series. [MSFD_8.pdf]

14. CPUE by Length a) b) c) d)
North Sea dab. a)shows the raw data. The red line indicates individuals above 50% maturity;
b) shows immature individuals as proxy for recruits; d) shows length converted to biomass of
mature (red) and all fish (black); c) shows total mortality Z over the respective previous two years
and scaled exploitation rate u+M, both as a proxies for F, with indication of M [MSFD_8.pdf].

15. CPUE by Length
North Sea dab: preliminary stock-recruitment relationship based on CPUE in weight as proxy
biomass of mature fish and number of young fish (= proxy-recruits) two years later, derived from
length composition in standardized survey catches. A hockey stick was fitted by a rule-based
procedure. The dotted vertical line indicates proxy SSBpa as the precautionary borderline to
potentially compromised recruitment. [MSFD_8.pdf]

16. CPUE by Length a) b) c) d)
North Sea dab. a)shows the raw data. The red line indicates individuals above 50% maturity;
b) shows immature individuals as proxy for recruits; d) shows length converted to biomass of
mature (red) and all fish (black); c) shows total mortality Z over the respective previous two years
and scaled exploitation rate u+M, both as a proxies for F, with indication of M [MSFD_8.pdf].

17. Peek Preview of Ongoing Research
For a population to sustain a history of output such as catch, it needs to have had a certain size and productivity
If you know the time series of annual production (biomass taken out for human use), and you know the productivity of the species, then you can calculate biomass and reference points

18. Catch-MSY Revisited Martell & Froese 2013
Output of the Catch-MSY method showing “viable” pairs surplus production rate r and
unexploited biomass k for North Sea cod. The red line indicates all r-k pairs that would result in
the same estimate of MSY; the red circle indicates the geometric. While the estimate of MSY is
robust, the geometric mean r = 0.24 depends on the lower bound for r.

19. k
Bmsy
Bpa
Icelandic cod: The black line shows the biomass predicted by the CMSY-method. The red line
shows observed total biomass. The vertical blue lines show the prior biomass windows used as
filters by the CMSY-method. The upper dashed line represents the unexploited biomass k, the
middle dotted line represents Bmsy, and the lower dashed line represents Bpa.

20. Exploitation Rate for Data-limited Stocks
umsy
Icelandic cod: exploitation rate catch/biomass as predicted by the CMSY method(black line)
and as observed (red line). The dotted line represents a proxy for MSY-compatible exploitation.

21. Conclusions
M is a good proxy for Fmsy and 2*Bpa is a good proxy for Bmsy
For most data-limited stocks in the ICES area, DATRAS contains sufficient information to estimate LWR, growth, maturity and relative abundance
Combining survey results with catch data leads to reasonable proxies for stock status and exploitation pressure
Length where 90% of the females reach maturity seems to be a reasonable lower limit reference point for mean length in commercial catches.