Transcript Document

Promotion of the FMSP Fishery Management
and Stock Assessment Guides
Part 2.
The ‘Stock Assessment Guide’
Presented at:
CRFM 2nd Annual Science Conference
Trinidad and Tobago, March 2006
By Dan Hoggarth, Scales Consulting Ltd
Reminder….
Two part set from project R8468:
I.
II.
How to manage a fishery – A simple guide to writing a fishery
management plan (the ‘Managers’ Guide’)
A guide to fisheries stock assessment using the FMSP tools
More detailed technical guide from project R8360:
• FAO Fisheries Technical Paper 487.
Stock assessment for Fishery Management. A framework
guide to the use of the FMSP stock assessment tools.
More details on stock assessments and models also available in
software help files
The ‘SA’ Guide - Table of Contents
Preface
1
2
3
4
5
6
Annexes
Annex 1.
Annex 2.
Annex 3.
Annex 2.
Annex 3.
What is the role of stock assessment in fishery management?
What is a stock assessment?
What tools can I use to make a stock assessment?
How do I select the best tool for the job?
How should I provide stock assessment advice to managers?
References
A checklist for fisheries scientists
Glossary of terms
The analytical approach to stock assessment using LFDA and Yield
The biomass dynamic approach to stock assessment using CEDA
Using the ParFish tool in data-limited situations and co-management
1. What is the role of Stock Assessment
in fishery management?
1.1 Providing advice in the preparatory phase
•
Identifying unit stock etc
1.2 Helping develop (and review) the management plan
•
•
•
Suggesting indicators and reference points
Strategic advice on alternative management options
Estimating uncertainty and advising on control rule options
1.3 Fine tuning in the implementation phase
•
Tactical advice (e.g. annually) on year-to-year adjustments in the
management measures
Stock assessment inputs over time
Preparing for
management planning
(situation analysis,
identify unit stock etc)
Years:
2006
Full strategic assessments to develop
the plan and then for reviews say
every 3-5 years in future (long term
advice)
‘07
‘08
2009
‘10
‘11
2012
‘13
‘14
Tactical assessments (short term advice) to monitor the
fishery indicators and adjust management controls as
needed, say every 1-2 years
Sections 1.1-1.3
2. What is a stock assessment?
A full strategic ‘SA’ should answer three key questions:
• "Where would we like to be?" - the values of specific reference points
selected by managers, as estimated for that fishery, updated for any new
data (e.g. the actual value of F that would give MSY).
• "Where are we now, relative to where we would like to be?" - an assessment
of the current status of the fishery as given by the indicators (e.g. the
estimate of Fnow).
• "What are the implications of alternative management scenarios, including
doing nothing?" - estimates of the effect on each indicator of those
management measures or controls identified as feasible for the fishery.
What is involved in a stock assessment?
Stock assessment process
NB:
Data/Inputs
Intermediate parameters
Full stock assessments require
both indicators & reference points
Indicators
Intermediate parameters are only
steps towards the real needs
Reference
points
Advice on management
options or needs, allowing for
risks and uncertainty
Example
Stock
Assessment
Elements
Data / Inputs




Catch, effort and abundance data
Size compositions (catch at age and length frequency data)
Biological data (sex, size at maturity, etc)
Other data: Social, economic, indigenous knowledge, etc
Intermediate parameters
Assessment
tools
FMSP software
 LFDA
 Yield
 CEDA
 ParFish
Other FMSP
tools/guidelines
 Age based
methods
 B&H invariant
methods
 Multi-species
guidelines
 Bayesian
approaches
 Empirical
approaches
Other tools
 FiSAT
 VPA
 BEAM4, etc
Used in models to estimate indicators and reference points, e.g.:
 Individual fish growth rates (K, L∞)
 Population growth rate (r) and carrying capacity (K)
 Natural mortality (M), maturity and reproduction (Lm50)
 Gear selectivity (e.g. Lc50), Catchability (q)
 Stock recruitment relationship
Fishery Indicators




Catch, effort (Cnow, fnow)
CPUE, Stock size (Bnow)
Fishing mortality rate (Fnow)
Others (social, economic,
ecological, governance etc)
Reference Points
 MSY-based (FMSY, BMSY)
 Proxies for MSY (e.g. F0.1)
 For maintaining reproductive
capacity (e.g. F%SSB, F%SPR)
 Risk-defined (e.g. Ftransient)
 Multispecies and ecosystem based
 Economic and social
Management advice
 Comparison of fishery indicators and reference points to provide
management advice allowing for uncertainty and risk
 Feedback for control rule management
 Management projections (short-term and long-term advice)
 Recognising multiple objectives and management options
Section 2.1
(and see FAO
FTP 487)
2.2 Are there alternative approaches to
stock assessment?
Yes….
Analytical / dynamic pool approach
(see e.g. Annex 3 - using LFDA and Yield software)
Biomass dynamic approach
(see e.g. Annex 4 - using CEDA software)
ParFish approach (see Annex 5)
And many other alternative approaches, software, models...
Biomass dynamic or analytical?
Biomass dynamic models like Schaefer surplus production model used
in CEDA and ParFish
• 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
Boxes 4 & 5, Table 7
2.3 What data would I need?
For the biomass dynamic approach
For the analytical approach
Multi-year time series of catch and
effort data, or catch and some other
index of abundance (e.g. from annual
surveys)
Short time series of catch composition
data (e.g. from length frequencies or
ageing studies)
Biological data (e.g. size at maturity)
(see Box 6)
(see Box 7)
3. What tools can I use to make a stock
assessment?
FMSP software tools:
•
•
•
•
Length Frequency Distribution Analysis (LFDA)
Yield
Catch Effort Data Analysis (CEDA)
Participatory Fisheries Stock Assessment (ParFish)
and many others
See FAO Fish. Tech. Paper 487 for details
see Box 8
see Box 9
see Box 10
see Box 11
3.1 What do the different FMSP stock assessment tools
estimate? (Table 5)
Indicators
Reference
points
x
Beverton
and Holt
invariants
x
Empirical
methods
ParFish
r, K, q
(production model)
K, L∞, t0
(von Bertalanffy growth)
M
(natural mortality rate)
Z
(total mortality rate)
YPR / BPR (yield / biomass per recruit)
Yield / biomass
(absolute, equilibrium)
Bt
(biomass in year t)
Nt
(numbers in year t)
Feq
(fishing mortality rate, Z-M)
CPUA
(catch per unit area)
MSY, fMSY, BMSY, FMSY
Fmax, F0.1, F0.x, F%SPR
(per recruit)
FMSY, F%SSB, Fcrash
(absolute)
Ftransient
(risk-based)
flim, Clim
(risk-based, biological limits)
fopt, Copt
(adjusted for ‘preferences’)
Fmax
(max yield per recruit)
FMSY
(max absolute yield)
CEDA
Intermediate
Yield
Available FMSP tools
LFDA
Parameters estimated
Type
Parameters
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
3.2 So what type of stock assessments can I use the
different tools for?
1
Beverton
and Holt
invariants
Empirical
methods
ParFish
CEDA
Yield
Management measures
Biological
studies
Options for strategic stock assessments of the long-term effects of alternative
management measures (Table 6)
2
x
Fishing effort (‘input’) controls, e.g. limited vessel licensing
x
x
x
3
2
Catch (‘output’) controls, e.g. quotas or ‘TACs’
x
x
x
x
Closed seasons
x
x
Changing size at first capture (e.g. with minimum legal
x
x
mesh size or fish size regulations)
Closed areas
x
x
1
In combination with LFDA or some other method of estimating current fishing mortality rate.
2
Per unit area.
3
If biomass also known.
1
x
3
x
3.2 And for short term tactical assessments…
At this stage, you just need to re-estimate your selected indicators to
see if you are meeting your targets or avoiding your limits (e.g. every 12 years)
As shown in Table 5…...
• If you are using Biomass-based reference points, use CEDA or ParFish
• If you are using F-based reference points, use LFDA or other (VPA)
4. How do I select the best tool for the job?
Step 1.
What tools could provide advice about the management controls
and standards (indicators and reference points) selected for the
fishery?
See Tables 5 and 6 as above
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 Tables 7 and 8 to help decide
See also Box 13 and Table 9 for process….
5. How should I provide stock
assessment advice to managers?
5.1
5.2
5.3
5.4
5.5
Providing strategic advice on alternative management options
Providing tactical advice to guide management by the control rules
Making projections: how long will it take to achieve the results?
How should I present the uncertainty in my analysis?
Giving advice in terms of risk
5.1 Providing strategic advice on alternative
management options
Remember, full strategic SA report should cover:
• "Where would we like to be?" - the values of specific reference points
selected by managers, as estimated for that fishery, updated for any new
data (e.g. the actual value of F that would give MSY, e.g. FMSY = 0.4).
• "Where are we now, relative to where we would like to be?" - an
assessment of the current status of the fishery as given by the indicators
(e.g. the estimate of Fnow).
• "What are the implications of alternative management scenarios, including
doing nothing?" - estimates of the effect on each indicator of those
management measures or controls identified as feasible for the fishery.
Providing strategic advice….
1
Use graphs or decision
tables to show the trade-offs
between the different
objectives
Graphs nice when only two
objectives, e.g. here
Add lines or symbols to
show current position on
curves
YPR reference points, e.g. F0.1,
where slope of YPR curve is
10% of that at the origin
0.8
0.6
0.4
SSBPR reference points, e.g.
F20%SPR, where SSBPR is 20% of
its unfished level
0.2
0
0
0.2 0.4 0.6 0.8
1
1.2 1.4 1.6 1.8
Fishing mortality rate, F
2
Or use decision tables when more
objectives to consider...
E.g. here from box 14 (could add more rows or columns…)
Management
Scenario 1
(No change)
Management
Scenario 2
e.g. F down 20%
Management
Scenario 3
e.g. mesh size
limit up 20%
Biological Indicators
e.g. Relative spawning per recruit (%SPR)
20 (11 – 29)
30 (20 – 40)
35 (26 – 44)
Economic Indicators
e.g. Relative yield per recruit (%YPR)
13 (10 – 16)
12 (9 – 15)
14 (11 – 17)
Mean catch value per fisher ($ ‘000)
5 (3 – 7)
5.8 (3.8 – 7.8)
5.4 (3.4 – 7.4)
Social Indicators
e.g. Change in number of fishers
0
-20%
0
Note: values in parentheses are 95% confidence intervals).
5.2 Providing tactical advice to guide
management by the control rules
e.g. mark position
of Fnow and Bnow
and show action
required
Flim
Fpa
Fishing
mortality
rate to be
allowed
next year
Blim
Bpa
Stock size this year
5.3 Making projections
1.
2.
Show how long it will take to achieve results
Allow for the fact that current biomass might be below optimum or target levels
(gives the basis of rebuilding plans for overexploited fisheries).
Can use Yield or CEDA software.
C. Predicted stock biomasses from 1968 with alternative TACs
1400
130 Kt
1200
Stock biomass (Kt)
140 Kt
1000
800
140 Kt, then 161 Kt
(MSY) after 1977
600
151 Kt (Replacement yield)
161 Kt (MSY)
400
170 Kt
200
Fit
0
1934
1939
1944
1949
1954
1959
1964
Year
1969
1974
1979
1984
1989
1994
1999
5.4 How should I present the uncertainty
in my analysis?
See boxes etc to illustrate use of confidence intervals, histograms of
parameter estimates, and sensitivity tests
Uncertainty can be used to adjust management advice to give
‘precautionary’ reference points, but….
… remember that the manager needs to decide what level of
precaution is appropriate (not the SA advisor), e.g. following
discussions with stakeholders
Outputs from ‘Yield’ showing uncertainty in
results given as histograms
Uncertainties in the control rule plot
(FMSY)
Flim
(%ileFMSY)
Fpa
Fishing control
RPs
(e.g. Fishing
mortality rate)
Blim
Bpa
Stock status RPs
(BMSY)
(%ileBMSY)
(e.g. Biomass)
5.5 Giving advice in terms of risk
Risk is formally defined as the probability of something bad or
undesirable happening
Risk assessment is one of the foundations of the precautionary
approach, and required by the FAO Code of Conduct for Responsible
Fisheries
You can provide advice in simple ways
•
•
e.g. by clarifying the risks of alternative reference points
or by showing confidence intervals or distributions
or more explicitly
•
e.g. using Yield’s Ftransient reference point (see Boxes 19 and 25)
Annex 1. A checklist for fisheries scientists
p 60
Annex 2. Glossary of terms
Analytical models
Bayesian approach
Beverton and Holt ‘invariant’ method
Biomass dynamic models
Carrying Capacity
CEDA
Decision control rules
Decision tables
Depletion models
Empirical models
FiSAT
Fishing mortality rate, F
FMSP
Growth overfishing
Indicator
Intermediate parameters
LFDA
Limit reference point
Management measures
Management strategy
Management standards
Mortality rates (see also fishing mortality rate)
Objectives
ParFish
‘Per recruit’ indicators and ref. points
Precautionary approach
Precautionary reference point
Production Model
Projection
Recruitment overfishing
Reference point
Risk
Scenario
Sensitivity analysis
SPR / SSBPR
Stock assessment (SA)
Stock assessment (SA) tools
Strategic stock assessments
Tactical stock assessments
Target reference point
Technical reference points
Uncertainty
Unit stock
Virtual Population Analysis (VPA)
von Bertalanffy growth function (VBGF)
‘Yield’
Annexes 3-5. Example Stock
Assessment Approaches
Annex 1.
Annex 2.
Annex 3.
The analytical approach to stock assessment using LFDA
and Yield
The biomass dynamic approach to stock assessment using
CEDA
Using the ParFish tool in data-limited situations and comanagement
These are not complete demonstrations of the software capabilities, nor
show all the options
But given as examples of how a SA could be carried out, and what
advice could be provided by each tool
Data / inputs
Assessment
tools
Intermediate
parameters
Indicators
Length
frequency
data
LFDA
Yield
The
analytical
stock
assessment
approach
using LFDA
and Yield
L∞, K, t0 (growth)
Z(-M)
Fnow(Eq)
Reference
points
Management
advice
Biological data,
management controls
(size limits, closed
seasons etc)
Per recruit
With SRR
Fmax
F0.1
F%SPR
FMSY
Ftransient
Compare to make management advice on F
e.g. if Fnow > FMSY, reduce F by management controls
if Fnow < FMSY, OK
Annex 3
‘per recruit’ or with recruitment?
Including recruitment in
analytical models
completely changes
results
Yield-per-R
Yield
But stock-recruit
relationship expensive
to get
So, if using per-recruit
models, give first priority
to LRPs for biomass per
recruit
SSB-per-R
SSB
0
0.5
1
1.5
2
Fishing mortality rate (F)
Box 24
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 agebased 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
Table 7
Data / inputs
Catch / effort
time series
Assessment
tools
CEDA
Intermediate
parameters
Indicators
Reference
points
Management
advice
Current catch /
effort data
The CEDA
stock
assessment
approach
r, K, q
Bnow
fnow
Cnow
(biomass
dynamic
model)
BMSY fMSY MSY
Compare to make management
advice on effort or catches
Annex 4
Data / inputs
Stock assess’t
interview data
or other priors
Catch /
effort time
series
Assessment
tools
ParFish
Intermediate
parameters
r, K, q
Indicators
Reference
points
Management
advice
Preference
interview
data
Current
catch / effort
data
ParFish
Bnow
fnow
flim
Clim
fopt
Cnow
The ParFish
stock
assessment
approach
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.
Annex 5