WP4: Models to predict

1
WP4 Models to predict test recovery strategies

• Cefas Laurence Kell John Pinnegar
• Univ. Aberdeen Tara Marshall Bruce McAdam

2
Objectives

• Evaluate alternative recovery strategies and
  identify the relative value of
• Information
• Control
• Synthesise available models and data on key
  processes that may affect stock recovery in a
  common framework
• Use framework to evaluate alternative management
  strategies that are robust to uncertainty
• Quantify and compare the impacts of alternative
  management strategies in order to produce a suite
  of strategies to achieve stock rebuilding

3
Tasks
1) Preparation of input data 2) Choice of
performance criteria and management
objectives 3) Specify base-case scenario 4)
Perform evaluations
4


Starting state


of system
Operating Model

Observation Error Model


generation of data on
represents the true dynamics of
fishery and stock(s)

the biological system against which
Simulation

performance will be measured

th
rough time

Current Stock Status
Future Stock Status
Management Procedure

Assess status of stock and set
management options depending upon
perceived status of fishery stock(s)

Performance Statistics

used to evaluate performance
of management procedures
against objectives

Recovery? Yield of target/non-target stocks
Figure 1. Conceptual framework
5
Framework for the Evaluation of Management
Strategies

• FEMS proposed and prototyped a generic framework
  known as FLR through a variety of contrasting
  case studies
• Why?
• Despite constant efforts made to regulate
  fisheries fishing capacity remains above that
  necessary to sustainable exploit marine
  resources.
• However, while the need to develop alternative
  management strategies is widely recognised it is
  almost impossible to develop these by conducting
  large-scale experiments on fish stocks. There has
  therefore been a trend towards the use of
  computer simulation to develop management
  strategies that meet multiple, but often
  conflicting management objectives, and are robust
  to uncertainty
• FLR is available from http//www.flr-project.org

6
Uncertainty

• Process error natural variability (in both time
  and space) in dynamic processes of the
  populations (e.g. recruitment, predation, growth
  and migration) and of the fisheries
• Model error related to the ability of model
  structure to capture the core of the system
  dynamics, many models are assumption rich but
  data poor
• Observation error related to collecting in-situ
  observations, such as total catch, catch
  composition (e.g. length, age, sex), research
  survey indices, effort
• Estimation error related to estimating
  parameters of various models used in the
  assessment procedure, such as growth models,
  stock-recruitment models, virtual population
  analyses, statistical models
• Implementation error because management actions
  are never implemented perfectly and may result in
  realised total catch, catch composition and
  effort that differ from those intended, e.g.
  misreporting.

7
Model Error?
Relates to the ability of any one model structure
to capture the core of the system dynamics, many
models are assumption rich but data poor. FEMS
was tasked by the European Commission with
specifying
Software Catalogue
8
Cod and Climate

• Hypotheses were that climate change acts through
• Growth, optimum temperature for growth
• Juvenile survival
• or
• Carrying capacity
• Therefore impacts on
• Recovery
• Long-term yields
• Sustainable levels

9
Management strategies

• Strategies investigated were either those adopted
  by or under consideration by the European
  Commission
• Short-term
• Recovery plans (30 increase in SSB)
• Long-term
• Harvest control rules (ensure F lt FPA and SSB gt
  BPA)

10
Recovery Plans

• Short-term
• Despite contrasting climate change hypothesises,
  magnitude of the change in temperature and the
  mechanism through which it acts (i.e. juvenile
  survival or carrying capacity), the predicted
  recovery time was little affected

• This was because recovery in the short term
  depended upon conserving fish that have already
  recruited

11
Recovery Plans

• Short-term
• Despite contrasting climate change hypothesises,
  magnitude of the change in temperature and the
  mechanism through which it acts (i.e. juvenile
  survival or carrying capacity), the predicted
  recovery time was little effected

• This was because recovery in the short term
  depended upon conserving fish that have already
  recruited

12
Long-term

• Scientific advice on safe biological limits to
  exploitation depends upon the correct hypothesis
• Reduced survival of recruits?
• Reduction in range?
• Since consequences are
• ?Flim if recruit survival reduced
• ?Blim if range reduced
• However, the correct mechanism can only be
  detected through biological studies rather than
  through stock assessment

13
North Sea Flatfish

• 100mm gt 55
• 80mm lt 55

• Plaice in the North
• Sole in the South

However, the distribution of plaice and sole
varies wrt 55
14
North Sea Flatfish

• 100mm gt 55
• 80mm lt 55

• Plaice in the North
• Sole in the South

However, the distribution of plaice or sole may
change wrt 55
The productivity of plaice and sole has also
changed over time
15
Cod and Climate

• Hypotheses were that climate change acts through
• Growth, optimum temperature for growth
• Juvenile survival
• or
• Carrying capacity
• Therefore impacts on
• Recovery
• Long-term yields
• Sustainable levels

16
Management strategies

• Strategies investigated were either those adopted
  by or under consideration by the European
  Commission
• Short-term
• Recovery plans (30 increase in SSB)
• Long-term
• Harvest control rules (ensure F lt FPA and SSB gt
  BPA)

17
Recovery Plans

• Short-term
• Despite contrasting climate change hypothesises,
  magnitude of the change in temperature and the
  mechanism through which it acts (i.e. juvenile
  survival or carrying capacity), the predicted
  recovery time was little affected

• This was because recovery in the short term
  depended upon conserving fish that have already
  recruited

18
Recovery Plans

• Short-term
• Despite contrasting climate change hypothesises,
  magnitude of the change in temperature and the
  mechanism through which it acts (i.e. juvenile
  survival or carrying capacity), the predicted
  recovery time was little effected

• This was because recovery in the short term
  depended upon conserving fish that have already
  recruited

19
Long-term

• Scientific advice on safe biological limits to
  exploitation depends upon the correct hypothesis
• Reduced survival of recruits?
• Reduction in range?
• Since consequences are
• ?Flim if recruit survival reduced
• ?Blim if range reduced
• However, the correct mechanism can only be
  detected through biological studies rather than
  through stock assessment

20
North Sea Flatfish

• 100mm gt 55
• 80mm lt 55

• Plaice in the North
• Sole in the South

However, the distribution of plaice and sole
varies wrt 55
21
North Sea Flatfish

• 100mm gt 55
• 80mm lt 55

• Plaice in the North
• Sole in the South

However, the distribution of plaice or sole may
change wrt 55
The productivity of plaice and sole has also
changed over time