Stock assessment for fishery management using the FMSP Tools

1
Stock assessment for fishery management - using
the FMSP Tools
FMSP Stock Assessment Tools Training
Workshop Bangladesh 19th - 25th September 2005
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Purpose of talk

• To show where the FMSP Tools may be used in the
  process of fishery management
• Complements Chapters 3-5 of FAO Fish. Tech. Pap.
  487

Chapters 3-5
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Content

• The stock assessment process
• Data collection for stock assessment
• Estimating intermediate parameters
• Estimating indicators
• Estimating technical reference points
• Risks of alternative reference points
• Providing stock assessment advice to managers
• ----------
• The FMSP Stock assessment tools
• What do they estimate?
• What can they provide advice on?
• How do you select the best tool for the job?

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The stock assessment process

• Collecting fishery data
• ( Estimating intermediary parameters )
• Estimating the current status of the fishery
  (indicators)
• Estimating technical reference points
• Providing management advice
• Monitoring and feedback

Chapter 3
5
The Stock Assessment Process
Figure 1.2
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Data collection for stock assessment

• Catch, effort and abundance (CPUE or
  survey-based)
• Catch compositions (length and/or age frequencies
  -gt F)
• Other biological data (maturity, fecundity etc)
• Section 3.2 focuses data needs for stock
  assessment (as above). See also below from FAO
• FAO. 1998. Guidelines for the routine
  collection of capture fishery data. Prepared at
  the FAO/DANIDA Expert Consultation. Bangkok,
  Thailand, 18-30 May 1998. FAO Fish. Tech. Pap.
  382. Rome, FAO. 113pp.
• Stamatopoulos, C. 2002. Sample based fishery
  surveys. A technical handbook. FAO Fish. Tech.
  Pap. 425. Rome, FAO. 132pp.

Section 3.2
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Estimating intermediate parameters

• Individual growth rates of fish (e.g. by LFDA)
• Population growth rate and carrying capacity
  (e.g. CEDA)
• Natural mortality rate (e.g. by Pauly equation)
• Exploitation pattern / gear selectivity
• Catchability (e.g. by CEDA)
• Maturity and reproduction
• Stock and recruitment (usually from VPA)
• Not of direct value, but used as inputs to
  fishery assessments
• Not constants, may vary over time (e.g. q, K etc)
• Values will usually be uncertain, so use
  sensitivity tests

Section 3.3
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Estimating indicators

• Catch (Grainger and Garcia method)
• --------------------------------------------------
  -----------------------------
• CPUE (approximate indicator of stock size)
• --------------------------------------------------
  -----------------------------
• Stock size (overall biomass by CEDA
• or stock size at age by VPA
• or relative abundance index by swept area
  survey)
• --------------------------------------------------
  -----------------------------
• Fishing mortality rate (F at age year by VPA
• or equilibrium F by catch curves)
• --------------------------------------------------
  -----------------------------
• Other performance indicators
• (e.g. of mature fish in catch, others re
  objectives)

Section 3.4
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Estimating technical reference points (1/3)

• MSY reference points (LRPs or TRPs)
• FMSY, BMSY or the MSY catch (Yield, CEDA or PFSA)
• Proxies for MSY reference points
• e.g. Fmax, F0.1, where no SR data (from Yield or
  Gulland eqn)
• Reference points for reproductive capacity (use
  as LRPs)
• From a stock-recruitment plot MBAL, BLOSS, Fmed
  etc
• From a stock-recr. relationship B50R, Fcrash
  etc
• From biomass per recruit F20SPR,
  F30SPR (Yield)
• From size limits based on size at maturity

Section 3.5
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Estimating technical reference points (2/3)

• Risk defined reference points
• Risk is inherently determined by
• selection of reference points (e.g. Fcrash is
  clearly a riskier reference point than FMSY), and
• distance between Flim and Fpa (percentile point
  selected) (see next slide)
• Set risk more explicitly using Yields Ftransient
  point
• F giving a specified probability (e.g. 10) that
  the SSB will fall below a specified level (e.g.
  20 of unexploited level) during a forward
  projection (e.g. of 20 years)

Section 3.5
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Risks of alternative reference points
Maximum Catch - FMSY
Fcrash riskier Point at which species becomes
extinct
Size of
Catch
Amount of Fishing
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Setting risk-based reference points
Low risk Bpa at 90th percentile of Blim
distribution
Blim (BMSY)
Bpa (ileBMSY)
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Setting risk-based reference points
Higher risk Bpa at 75th percentile of Blim
distribution
Blim (BMSY)
Bpa (ileBMSY)
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Estimating technical reference points (3/3)

• Multi-species and ecosystem-based reference
  points
• Focus on technical interactions and avoidance of
  bycatch and discarding problems etc
• In CCAMLR, target fisheries may be closed if a
  bycatch limit is reached for a bycatch species
• Economic and social reference points
• E.g. MEY, indices of employment income or
  profitability (resource rent) distribution of
  benefits (e.g. the percentage of the catch
  allocated to industrial and artisanal fisheries)
• emphasises tradeoffs in objectives, e.g. between
  the catch rate and the total catch, and between
  the economic efficiency and employment.

Section 3.5
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Providing management advice

• Annual feedback for control rule management
  (where a full decision control system already in
  place and agreed)
• Long-term decision analyses (every few years?)
• Making projections short-term and medium-term
  advice (emphasising the current state of the
  stock, and the likely time it will take to
  recover see Yield and CEDA presentations)
• Recognising multiple objectives and management
  options
• present as graphs or decision tables
• Providing advice on uncertainty and risk
• using sensitivity tests,
• or by estimating risk-based reference points

Section 3.6
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A simple decision table format
Indicators

• Repeat table for each uncertainty or alternative
  state of nature

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• Flow of information between managers and stock
  assessment advisors in developing and
  implementing a management plan
• See also checklist of SA needs in new document

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Options for alternative SA approaches

• Following slides summarise Section 3.1 of FAO
  Document

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Deterministic or stochastic?

• Deterministic models always give the same answer
• Stochastic models allow for uncertainty in the
  inputs and estimate the uncertainty in the
  outputs.
• CEDA, Yield and PFSA software all give stochastic
  outputs

Section 3.1.2
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Biomass dynamic or analytical?

• Biomass dynamic models like Schaefer surplus
  production model used in CEDA and PFSA
• relate fishery outputs (catch) directly to inputs
  (effort)
• Useful where fish are hard to age used to set
  quotas and effort
• Analytical models used in Yield and other per
  recruit and dynamic pool approaches
• include intermediary processes, both biological
  and fishery (e.g. from LFDA)
• may be length-based or age-based
• Needed for management advice on size limits,
  seasons etc
• Neither approach is more right or wrong than the
  other they are just based on different models
  and assumptions

Section 3.1.3
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Equilibrium or dynamic?

• Modern biomass dynamic fitting methods all use
  non-equilibrium dynamic approaches
• Older methods (e.g. plotting CPUE vs f) would
  always enable some model to be fitted, due to
  correlation in variables, but often WRONG
• Non-equilibrium methods will sometimes fail to
  find any reasonable solution, e.g. due to lack of
  contrast in data
• Better to recognise limitations of data rather
  than use an incorrect equilibrium model

Section 3.1.4
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Age-based or length-based?

• ELEFAN, FiSAT II etc largely promoted
  length-based methods for tropical fisheries.
  FMSP LFDA software also length-based
• Four FMSP projects, however, have confirmed the
  benefits of age-based approaches, wherever fish
  can be aged (e.g. using otolith readings) more
  accurate etc
• Age-based methods now used for deep slope
  snapper fisheries in FMSP study sites in
  Seychelles
• Length-based methods better where fish really can
  not be aged (e.g. crustacea), or where ageing is
  v. expensive

Section 3.1.5, Chapter 10
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per recruit or with recruitment?

• Including recruitment in analytical models
  completely changes results
• But stock-recruit relationship expensive to get
• So, if using per-recruit models, give first
  priority to LRPs for biomass per recruit

Section 3.2
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The FMSP Stock Assessment Tools

• Following FMSP outputs covered in FAO FTP 487
• LFDA software - estimating growth and mortality
  rates
• Reference points from minimal population
  parameters
• Yield software - estimating reference points for
  YPR etc
• Management of multi-species fisheries
• CEDA software - biomass dynamic / surplus
  production models
• ParFish software - for data-limited situations
  co-management
• Empirical methods
• Special approaches for inland fisheries

Chapter 4 and Parts 2/3
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The analytical stock assessment approach using
LFDA and Yield
Biological data, management controls (size
limits, closed seasons etc)
Length frequency data
Data / inputs
LFDA
Yield
Assessment tools
Intermediate parameters
L8, K, t0 (growth)
Indicators
Z ( - M ) Fnow(Eq)
Per recruit Fmax F0.1 FSPR
With SRR FMSY Ftransient
Reference points
Compare to make management advice on F e.g. if
Fnow gt FMSY, reduce F by management controls
if Fnow lt FMSY, OK
Management advice
Figure 4.1
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The CEDA stock assessment approach (DRP / biomass
dynamic model)
Current catch / effort data
Catch / effort time series
Data / inputs
Assessment tools
CEDA
Intermediate parameters
r, K, q
Bnow
fnow Cnow
Indicators
Reference points
BMSY fMSY MSY
Compare to make management advice on effort or
catches
Management advice
Figure 4.5 Section 4.5
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The ParFish stock assessment approach
Current catch / effort data
Catch / effort time series
Stock assesst interview data or other priors
Preference interview data
Data / inputs
Assessment tools
ParFish
ParFish
Intermediate parameters
r, K, q
Indicators
fnow Cnow
Bnow
Reference points
flim Clim
fopt Copt
Management advice on effort or catch controls, in
terms of limit and target levels. Targets
(fopt,Copt) incorporate the preferences of
resource users. Limits are based on the risk
that B will be reduced below a specified of K.
Management advice
Figure 4.10 Section 4.6
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What do the different FMSP stock assessment
tools estimate? (Table 5 of new guide)
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Which tools can be used to provide advice for
different management measures (Table 6 of new
guide)
See also Section 2.5.5 in FTP 487
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How to select the best tool for the job?

• Step 1. Decide the goals, objectives and
  standards first.
• What tools could provide advice about the
  management controls and standards (indicators and
  reference points) selected for the fishery?
• See Tables 5 and 6 of new SA guide
• Note that several tools might be suitable, so...
• Step 2. Of the tools and approaches available,
  what is the most appropriate to the local
  situation?
• See pros and cons tables to help decide
• See also Box 13 and Table 9 of new guide for
  process.