Transcript PowerPoint

Climate Change and
Implications for Management
of North Sea Cod (Gadus
morhua)
L.T. Kell, G.M. Pilling and C.M. O’Brien
CEFAS, Lowestoft
1
Acknowledgements
This paper was prepared with funding support
provided by the Commission of the
European Communities Directorate General
for Fisheries (DG XIV) and by the
Department for Food, Environment and
Rural Affairs (UK).
2
Objectives
• Evaluate whether management strategies for
North Sea cod i.e.
– Recovery plans
– Harvest Control Rules
are robust to plausible hypotheses about
climate change
• Whether climate change is the most
important factor for management
3
Methodology ~ Simulation
IWC, MATACS/MATES
• Experimental approach using
computer simulation.
– Operating Model
• Hypotheses about Stock and
Fishery dynamics
– Management Procedure
• Alternative Assessment and
management options
• Experimental treatments correspond to hypotheses
about dynamics
• Can includes a wide range of uncertainty
4
Uncertainty
Sources of uncertainty implicitly considered
• Process Error
– Recruitment, somatic growth, natural mortality
• Measurement Error
– Occurs when collecting observations from a population
• Estimation Error
– Arises during the assessment process
• Model Error
– Models used within assessment procedures will never capture the true complexity
of the dynamics
• Implementation Error
– Management actions are never implemented perfectly
5
Climate Change Hypotheses
Climate change acts through temperature on
• Growth (weight-at-age):
– Optimum temperature for growth
• Stock Recruitment Relationship
– Juvenile survival
– Carrying capacity
6
Temperature scenarios
10
SST (°C)
9
8
7
6
1960
1980
Observed
2000
2001
2020
Hadley Low
2040
2060
Const. Increase
7
Annual increase
Weight-at-age ~ f(T)
Age 3
Age 5
Impacts on selectivity by gear,
discarding practice and SSB
Temperature
8
Stock Recruitment ~ Ricker
R  Se
500000
450000
 S
Recruitment
400000
350000
300000
250000
200000
150000
100000
Biomass at maximum recruitment
50000
0
0
200000
400000
600000
800000
1000000
1200000
1400000
SSB
2001
9
Stock Recruitment ~ (T)
R  Se
500000
450000
 S
Recruitment
400000
350000
300000
250000
200000
150000
100000
Biomass at maximum recruitment
50000
0
0
200000
400000
600000
800000
1000000
1200000
1400000
SSB
2001
Hadley Low 2030
10
Stock Recruitment ~ (T)
R  Se
500000
450000
 S
Recruitment
400000
350000
300000
250000
200000
150000
100000
Biomass at maximum recruitment
50000
0
0
200000
400000
600000
800000
1000000
1200000
1400000
SSB
2001
Hadley Low 2030
Const. Increase 2030
11
Stock Recruitment ~ (T)
R/S at origin
R  Se
500000
450000
 S
Recruitment
400000
350000
300000
250000
200000
150000
100000
50000
0
0
200000
400000
600000
800000
1000000
1200000
1400000
SSB
2001
Hadley Low 2030
Const. Increase 2030
12
Stock Recruitment ~ (T)
R  Se
500000
450000
 S
Recruitment
400000
350000
300000
250000
200000
150000
100000
50000
0
0
200000
400000
600000
800000
1000000
1200000
1400000
SSB
2001
Hadley Low 2030
Const. Increase 2030
13
Productivity Curve
R  Se
 S
300000
Alpha - Hadley Low
Alpha - Const Increase
Yield
2000
0
Fcrash = 0.72 0.78 0.87
0
1500000
SSB
~ Juvenile Survival
Affects fishing mortality
Reference points (FMSY,
FCrash)
14
Productivity Curve
R  Se
 S
~ Carrying Capacity
300000
Affects biomass
reference points (BMSY,
Blim, BPA)
Alpha - Hadley Low
Alpha - Const Increase
Yield
2000
300000
Beta - Hadley Low
Beta - Const Increase
0
Fcrash = 0.72 0.78 0.87
0
1500000
Yield
2000
SSB
~ Juvenile Survival
Affects fishing mortality
Reference points (FMSY,
FCrash)
0
0
Fcrash = 0.87
1500000
SSB
15
Management Strategies
Strategies investigated were either those adopted
by the European Commission or currently
under consideration by the Commission
• Short-term
– Recovery plans
• Long-term
– Harvest Control Rules
16
Short-term Management Strategies
• North Sea cod Recovery Plan (Adopted in
December 2003)
– Set Catch each year so that SSB increases by
30% annually until stock recovers to 150,000 t
(BPA)
17
Results
• Predicated upon the assumptions used in the
simulation experiments
• Don’t allow us to predict what will happen
• Allow us to investigate the relative
importance of the various processes and the
interactions between them
18
Recovery ~ Climate Change
Probability of Recovery
1.0
2001
0.5
Low ~ Alpha
High ~ Alpha
Low ~ Beta
High ~ Beta
0.0
2000
2005
2010
2015
Year
19
Recovery ~ Climate Change
100%
% Contribution
Probability of Recovery
1.0
0.5
75%
50%
25%
0%
2000
2005
Year
0.0
2000
2005
Most of the biomass during the recovery
period is
from year-classes
recruited prior
2010
2015
to implementation of the recovery plan
Year
20
Recovery ~ Yields
300000
2001
Low ~ Alpha
High ~ Alpha
Expected Yield
Low ~ Beta
High ~ Beta
0
2000
2002
2004
Year
2006
2008
2010
21
Recovery ~ Climate Change
Probability of Recovery
1.0
2001
0.5
Low ~ Alpha
High ~ Alpha
Low ~ Beta
High ~ Beta
0.0
2000
2005
2010
2015
Year
22
Recovery ~ In a mixed fishery?
Probability of Recovery
1.0
2001
Low ~ Alpha
0.5
High ~ Alpha
Low ~ Beta
High ~ Beta
Cod Bycatch
0.0
2000
2005
Year
2010
2015
23
Recovery ~ But will we know?
Probability of Recovery
1.0
2001
Low ~ Alpha
High ~ Alpha
0.5
Low ~ Beta
High ~ Beta
Cod Bycatch
Perceived
0.0
2000
2005
Year
2010
2015
24
Long-term Management Strategies
• Harvest Control Rules where Total
Allowable Catches (TACs) are set for a
target Fishing Mortality
– Target F = 0.65 (FPA defined by ICES)
– Target F = 0.45
F
– ICES HCR
• F reduced if SSB < BPA
F = 0.65
BPA
SSB
25
Management Objectives
• Sustainability
– SSB > BPA (SSB at which spawning impaired)
• Yields
• Stability of Yields (long-term planning)
26
Harvest Control Rules ~ Results
Rela tive to F=0.65 with no clima te cha nge
SSB
F= 0.65
F=0.45
HC R
Yield
F= 0.65
F=0.45
HC R
AV Yield
F= 0.65
F=0.45
HC R
Ha d le y Lo w
A lp ha
C o nst Inc re a se
A lp ha
Ha d le y Lo w
Be ta
C o nst Inc re a se
Be ta
85%
164%
86%
76%
155%
79%
70%
123%
70%
63%
111%
64%
Ha d le y Lo w
A lp ha
C o nst Inc re a se
A lp ha
Ha d le y Lo w
Be ta
C o nst Inc re a se
Be ta
85%
100%
90%
77%
94%
82%
70%
75%
73%
66%
67%
66%
Ha d le y Lo w
A lp ha
C o nst Inc re a se
A lp ha
Ha d le y Lo w
Be ta
C o nst Inc re a se
Be ta
18%
15%
21%
18%
15%
22%
18%
15%
24%
18%
15%
26%
27
Results
• Yields of North Sea cod at the levels seen in the
1980’s could be achieved if fishing mortality
reduced and fisheries managed on a mixed stock
basis
28
Conclusions I
• Climate Change has little effect in short-term
• Management of fleets in the mixed North Sea
fisheries more important, especially if
distribution of stocks change
• Can not easily estimate changes in MSY or BMSY
• As important to understand the mechanism
through which climate change acts as well as to
quantify the magnitude of change
• Unlikely to determine this solely through stock
assessment or analyses based upon VPA
29
Conclusions II
• Do not try to make Stock Assessment more
complex by including environmental
covariates
• Develop simpler management procedures that
meet management objectives and are robust to
uncertainty about the true dynamics
• Do this by evaluating candidate strategies
against plausible hypotheses about ecological,
environmental, fishery processes and the
interactions between these processes
30