MSFD Indicators and Reference
Points for Data-Limited Stocks
Rainer Froese
GEOMAR
EU-BON Workshop, Leipzig
18 February 2014
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
MSFD Descriptor 3
1. 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.
2. The spawning stock biomass SSB relative to the one that can
produce the maximum sustainable yield (SSBmsy) or other suitable
biomass indices.
3. The age and size distribution within the population, with the subindicators
i. Proportion of fish larger than the mean size of first sexual
maturation;
ii. Mean maximum length across all species found in research
vessel surveys;
iii. 95 % percentile of the fish length distribution observed in
research vessel surveys;
iv. Size at first sexual maturation [relative to historic sizes], which
may reflect the extent of undesirable genetic effects of
exploitation.
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
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
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. 2012.
Thus, M can be used as a proxy for Fmsy
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
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
DATRAS: Millions of Survey Records
http://datras.ices.dk
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 = 0.007 * Length3.16
[SMALK_Analysis_25.r]
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]
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]
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]
CPUE by Length
a)
c)
b)
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].
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]
CPUE by Length
a)
c)
b)
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].
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
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.
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.
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.
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.