Office of Science and Technology
Kristan Blackhart, National Stock Assessment Program Lead, NOAA Fisheries Office of Science and TechnologyMelissa Karp, Fisheries Science CoordinatorECS Federal in support of NOAA Fisheries National Stock Assessment Program
Stock Assessments in Support of U.S. Fisheries
U.S. Department of Commerce | National Oceanic and Atmospheric Administration | National Marine Fisheries ServicePage 2
• Understand the context for stockassessments in fisheries management
• Learn about data supporting assessmentsand the assessment process
• Get ready for live discussion and Q&A• Prepare for exercise where you will
interpret assessment advice to makemanagement decisions
U.S. Department of Commerce | National Oceanic and Atmospheric Administration | National Marine Fisheries ServicePage 3
• “…prevent overfishing whileachieving…optimum yield”NS1
• “…best scientificinformation available”NS2
• “…an individual stock…shallbe managed as a unitthroughout its range”NS3
Magnuson-Stevens Act
Stock Assessments Supporting Management
U.S. Department of Commerce | National Oceanic and Atmospheric Administration | National Marine Fisheries ServicePage 4
• 8 FMCs, 46 FMPs,450+ stocks
• 16+ management& advisoryorganizations
SUPPORTING
• 6 Science Centers• 20+ labs• Headquarters,
OST, NSAP• 5 Regional Offices
NOAA Fisheries Science
U.S. Department of Commerce | National Oceanic and Atmospheric Administration | National Marine Fisheries ServicePage 5
We use mathematical models to answer two basic questions…
The primary scientific basis for successful and sustainable fisheries
What is a Stock Assessment?
U.S. Department of Commerce | National Oceanic and Atmospheric Administration | National Marine Fisheries ServicePage 6
How much is too much?2What level of catch is sustainable?
Is everything OK? 1What is the status of the stock?
U.S. Department of Commerce | National Oceanic and Atmospheric Administration | National Marine Fisheries ServicePage 7
Northern Stock
Southern Stock
Biological Stocks• Group of individuals of the same species• Inhabit the same geographic region• Mix and interbreed when mature
Management Stocks• Often the same as biological stocks• Exceptions include multispecies complexes, breaks at
geopolitical boundaries
Defining “Stock”
U.S. Department of Commerce | National Oceanic and Atmospheric Administration | National Marine Fisheries ServicePage 8
U.S. Department of Commerce | National Oceanic and Atmospheric Administration | National Marine Fisheries ServicePage 9
Fishery-Independent: Scientific Surveys• Statistical sampling design• Covers full stock range• Uses standardized gear and practices• Extractive methods (e.g., trawl, longline,
H/L, pot, trap, gill net, etc.)• Non-extractive methods (e.g., acoustic,
video, aerial, diving, tag/recapture, etc.)
Data Collection & Processing: Abundance
U.S. Department of Commerce | National Oceanic and Atmospheric Administration | National Marine Fisheries ServicePage 10
Fishery-Dependent: Commercial / Recreational Fisheries• Catch per unit of effort (CPUE)• May not reflect abundance ─ market
dynamics and changing practices• Uneven distribution of effort
Fishery-Independent: Scientific Surveys• Statistical sampling design• Covers full stock range• Uses standardized gear and practices• Extractive methods (e.g., trawl, longline,
H/L, pot, trap, gill net, etc.)• Non-extractive methods (e.g., acoustic,
video, aerial, diving, tag/recapture, etc.)
Data Collection & Processing: Abundance
U.S. Department of Commerce | National Oceanic and Atmospheric Administration | National Marine Fisheries ServicePage 11
Good Habitat
Bad Habitat
Bad Habitat
Hyperstability
U.S. Department of Commerce | National Oceanic and Atmospheric Administration | National Marine Fisheries ServicePage 12
Hyperstability
U.S. Department of Commerce | National Oceanic and Atmospheric Administration | National Marine Fisheries ServicePage 13
Hyperstability
U.S. Department of Commerce | National Oceanic and Atmospheric Administration | National Marine Fisheries ServicePage 14
Hyperstability
U.S. Department of Commerce | National Oceanic and Atmospheric Administration | National Marine Fisheries ServicePage 15
Hyperstability
U.S. Department of Commerce | National Oceanic and Atmospheric Administration | National Marine Fisheries ServicePage 16
Hyperstability
U.S. Department of Commerce | National Oceanic and Atmospheric Administration | National Marine Fisheries ServicePage 17
Hyperstability
U.S. Department of Commerce | National Oceanic and Atmospheric Administration | National Marine Fisheries ServicePage 18
Hyperstability
U.S. Department of Commerce | National Oceanic and Atmospheric Administration | National Marine Fisheries ServicePage 19
-
50,000
100,000
150,000
200,000
250,000
300,000
350,000
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
Year
Surve
y Biom
ass
0
0.2
0.4
0.6
0.8
1
1.2
Catch
rate
(lbs/h
ook)
BiomassCatch rate
Hyperstability
U.S. Department of Commerce | National Oceanic and Atmospheric Administration | National Marine Fisheries ServicePage 20
Data Sources• Fishery-independent surveys• Fisheries observers• Port sampling• Research & tagging studies• Cooperative research
Data Types• Age• Length & Weight• Fecundity• Natural Mortality• Growth• Recruitment• Movement • Environmental influences• Predation• Diet… and more!
Data Collection & Processing: Biology
U.S. Department of Commerce | National Oceanic and Atmospheric Administration | National Marine Fisheries ServicePage 21
Data Sources• Fishery Information Networks (state,
federal, interstate commissions)• Dockside monitoring• Logbooks• Observer programs• Marine Recreational Information
Program (MRIP)
Data Types• Commercial landings• Commercial discards• Recreational catch• Recreational releases• Research removals• Survival rate
Data Collection & Processing: Catch
U.S. Department of Commerce | National Oceanic and Atmospheric Administration | National Marine Fisheries ServicePage 22
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Stock Size
Bt+1= Bt + Rt + Gt – Mt - Ft Fishing
* Landings * Discards/Survival * Selectivity
Natural Mortality
* Predation * Disease * Etc.
Growth
* Length * Weight
Reproduction
* Maturity * Fecundity * Stock-Recruit
Population Dynamics Modeling Basics
U.S. Department of Commerce | National Oceanic and Atmospheric Administration | National Marine Fisheries ServicePage 24
Prod
ucti
on
Biomass
Pretty Good Yield
Lower effort neededHigher catch ratesLess fluctuationsLarger fishLess ecosystem impactBuffer uncertainty
BMSY
What is Sustainable?
U.S. Department of Commerce | National Oceanic and Atmospheric Administration | National Marine Fisheries ServicePage 25
0
5
0
5
0
5
0
5
0
5
1964
2001
Stock Biomass
Catc
h
Prod
ucti
on
Abundance
Assessment Modeling: Cartoon vs. Reality
U.S. Department of Commerce | National Oceanic and Atmospheric Administration | National Marine Fisheries ServicePage 26
DataReq’s
• Length- or age-structured, incorporating complete information• Stock status and forecasts of catch limits relative to ref. points
Statistical Catch-at-Age/Length (SCAA/SCAL)
• Abundance-at-age calculated backwards in time• Analyses can help provide complete advice on status, forecasts
Virtual Population Analysis (VPA)
• Requires at least one abundance index, but not age-specific• Provides estimates of MSY, B/Bmsy, F/Fmsy, catch @ Fmsy
Aggregate Biomass Dynamics
• Time series analysis of fishery or survey trends• Provides mostly qualitative advice about stock trendsIndex-Based
• Many are catch only; some use biological info• Provides management advice in relative termsData-Limited
Types of Assessment Models
U.S. Department of Commerce | National Oceanic and Atmospheric Administration | National Marine Fisheries ServicePage 27
• Models are simplifications• Choosing a model can
depend on:• Data availability• Stock biology• Stock importance
• Multiple methods may beappropriate
Science is really in the business of disproving current
models or changing them to conform to new information. In
essence, we are constantly proving our latest ideas wrong.”
David Suzuki
“…all models are approximations. Essentially, all models are wrong, but some are
useful. However, the approximate nature of the model must always be borne in mind…”
George E.P. Box
Choosing Assessment Methods
U.S. Department of Commerce | National Oceanic and Atmospheric Administration | National Marine Fisheries ServicePage 28
U.S. Department of Commerce | National Oceanic and Atmospheric Administration | National Marine Fisheries ServicePage 2 U.S. Department of Commerce | National Oceanic and Atmospheric Administration | National Marine Fisheries ServicePage 2
Key Areas of Advice…
• What are the sustainable biological limits to fishing (i.e. FMSY
and BMSY)?
• How hard have we been fishing and what is the current stockstatus?
• What fraction of the stock should be harvested each year?
• Harvest Policy & Control Rules
• What short-term future catch level (forecast) wouldimplement the harvest policy given the current stock statusand prevailing environmental conditions?
U.S. Department of Commerce | National Oceanic and Atmospheric Administration | National Marine Fisheries ServicePage 3 U.S. Department of Commerce | National Oceanic and Atmospheric Administration | National Marine Fisheries ServicePage 3
Stock Status
• Current fishing rateand biomass levelsrelative tomanagementreference points
0
1
2
0 0.5 1 1.5 2
Fis
hin
g M
ort
ality
/ L
imit
Abundance / MSY Target
Overfishing,Overfished
Overfished Stock abundant,not Overfishing
Overfishing,Stock declining
but still abundant
TARGET
Overfishing,Stock declining
Rebuilding
U.S. Department of Commerce | National Oceanic and Atmospheric Administration | National Marine Fisheries ServicePage 4 U.S. Department of Commerce | National Oceanic and Atmospheric Administration | National Marine Fisheries ServicePage 4
Proactive Short-Term Advice: Catch Levels
• In accordance with harvest policy
• No more than specified (<=50%) chance ofoverfishing
• Rebuild overfished stocks
• Maximize benefits while protecting marineecosystems
• Control Rule: Formula that calculates future catch levelfrom forecasted biomass
U.S. Department of Commerce | National Oceanic and Atmospheric Administration | National Marine Fisheries ServicePage 5 U.S. Department of Commerce | National Oceanic and Atmospheric Administration | National Marine Fisheries ServicePage 5
Proactive Short-Term Advice: Catch Levels
SSC
Council
ABC Control Rule
U.S. Department of Commerce | National Oceanic and Atmospheric Administration | National Marine Fisheries ServicePage 1 U.S. Department of Commerce | National Oceanic and Atmospheric Administration | National Marine Fisheries ServicePage 1
Proactive Short-Term Advice: Uncertainty• Uncertainty is the Reality
• Models are simplifications & data are incomplete• Uncertainty ≠ bad science
• Scientific Uncertainty• Data/Observation: sampling variability from surveys,
error in observations, lack of information• Model/Assessment: arises during the modeling and
assessment process and includes: parameter uncertainty, accuracy of assumptions, choice of modeling approach
• Ecosystem: unknown or poorly understood ecosystemrelationships and their effects on single-speciesmanagement advice
• Management Uncertainty• Implementation: uncertainty in performance of
management actions, leading to uncertainty in whetherthe target is being met
1980 1985 1990 1995 2000 2005 2010
Nor
mal
ized
inde
x
Domestic RPN
GOA Trawl Survey
IFQ Fishery
Derby Fishery
U.S. Department of Commerce | National Oceanic and Atmospheric Administration | National Marine Fisheries ServicePage 7 U.S. Department of Commerce | National Oceanic and Atmospheric Administration | National Marine Fisheries ServicePage 7
Proactive Short-Term Advice: Uncertainty
• Methods for characterizing scientific uncertainty:
• Statistical error
• Sensitivity analysis
• Multiple models
• Retrospectiveanalysis
Image sources:
https://science.howstuffworks.com/nature/climate-weather/storms/spaghetti-models.htm
ICES J Mar Sci, Volume 72, Issue 1, January 2015, Pages 99–110, https://doi.org/10.1093/icesjms/fsu198
U.S. Department of Commerce | National Oceanic and Atmospheric Administration | National Marine Fisheries ServicePage 8 U.S. Department of Commerce | National Oceanic and Atmospheric Administration | National Marine Fisheries ServicePage 8
Proactive Short-Term Advice: Uncertainty
• Methods for characterizing scientific uncertainty:
• Statistical error
• Sensitivity analysis
• Multiple models
• Retrospectiveanalysis
Image sources:
https://science.howstuffworks.com/nature/climate-weather/storms/spaghetti-models.htm
ICES J Mar Sci, Volume 72, Issue 1, January 2015, Pages 99–110, https://doi.org/10.1093/icesjms/fsu198
U.S. Department of Commerce | National Oceanic and Atmospheric Administration | National Marine Fisheries ServicePage 9 U.S. Department of Commerce | National Oceanic and Atmospheric Administration | National Marine Fisheries ServicePage 9
Proactive Short-Term Advice: Uncertainty
• Methods for characterizing scientific uncertainty:
• Statistical error
• Sensitivity analysis
• Multiple models
• Retrospectiveanalysis
Image sources:
https://science.howstuffworks.com/nature/climate-weather/storms/spaghetti-models.htm
ICES J Mar Sci, Volume 72, Issue 1, January 2015, Pages 99–110, https://doi.org/10.1093/icesjms/fsu198
U.S. Department of Commerce | National Oceanic and Atmospheric Administration | National Marine Fisheries ServicePage 10 U.S. Department of Commerce | National Oceanic and Atmospheric Administration | National Marine Fisheries ServicePage 10
Proactive Short-Term Advice: Uncertainty• SSCs expected to address scientific
uncertainty with ABCs (safety buffer)
• P* harvest control rule
• Fig: uncertainty around OFL
• P* = P* is the allowable probability that the ABC
will exceed the OFL (overfishing). Should not
exceed 50%
U.S. Department of Commerce | National Oceanic and Atmospheric Administration | National Marine Fisheries ServicePage 2 U.S. Department of Commerce | National Oceanic and Atmospheric Administration | National Marine Fisheries ServicePage 2
Proactive Short-Term Advice: Uncertainty• SSCs expected to address scientific
uncertainty with ABCs (safety buffer)
• P* harvest control rule• Fig: uncertainty around OFL• P* = P* is the allowable probability that the ABC
will exceed the OFL (overfishing). Should notexceed 50%
• Using P* = 40% identifies anABC that has 40% chance ofexceeding true OFL
• Council determines P* through their Risk Policy
• Multiplier approach: ABC = 0.75*OFL
U.S. Department of Commerce | National Oceanic and Atmospheric Administration | National Marine Fisheries ServicePage 3 U.S. Department of Commerce | National Oceanic and Atmospheric Administration | National Marine Fisheries ServicePage 3
Uncertainty and the Data-Poor Situation• MSY or proxies cannot be calculated
• Catch level that constitutesoverfishingis unknown
• Statistical uncertainty may berelatively low with data-poor methods
• However, the buffer should increasewith less information• Need to account for unmeasured
(likely) uncertainty• Size of buffer can be “borrowed”
from similar species (should not beless)
U.S. Department of Commerce | National Oceanic and Atmospheric Administration | National Marine Fisheries ServicePage 13 U.S. Department of Commerce | National Oceanic and Atmospheric Administration | National Marine Fisheries ServicePage 13
Uncertainty & Decision Support Tools
• Decision Tables
• Show expected outcomes given a range ofmanagement decisions and assessmentscenarios
• Communicates risks and tradeoffs
U.S. Department of Commerce | National Oceanic and Atmospheric Administration | National Marine Fisheries ServicePage 14 U.S. Department of Commerce | National Oceanic and Atmospheric Administration | National Marine Fisheries ServicePage 14
Uncertainty & Decision Support Tools
• Decision Tables
• Show expected outcomes given a range ofmanagement decisions and assessmentscenarios
• Communicates risks and tradeoffs
• Management Strategy Evaluations
• Uses computer simulation to run manytimes to reveal the performancecharacteristics of an entire fisheryscience-to-management process
U.S. Department of Commerce | National Oceanic and Atmospheric Administration | National Marine Fisheries ServicePage 15 U.S. Department of Commerce | National Oceanic and Atmospheric Administration | National Marine Fisheries ServicePage 15
Uncertainty & Decision Support Tools
• Decision Tables
• Show expected outcomes given a range ofmanagement decisions and assessmentscenarios
• Communicates risks and tradeoffs
• Management Strategy Evaluations
• Uses computer simulation to run manytimes to reveal the performancecharacteristics of an entire fisheryscience-to-management process
• Example: Gulf of Mexico red-tide events
U.S. Department of Commerce | National Oceanic and Atmospheric Administration | National Marine Fisheries ServicePage 16 U.S. Department of Commerce | National Oceanic and Atmospheric Administration | National Marine Fisheries ServicePage 16
Assessments designed to answer management questions
Abundance, biology, and catch are key inputs
Variety of advanced technical methods tuned to diverse data availability scenarios
Assessments produce estimates of stock abundance, fishing mortality, and productivity
Stock forecasts provide technical basis to guide setting Annual Catch Limits
Summary
U.S. Department of Commerce | National Oceanic and Atmospheric Administration | National Marine Fisheries ServicePage 17 U.S. Department of Commerce | National Oceanic and Atmospheric Administration | National Marine Fisheries ServicePage 17
For More Information
NMFS Stock Assessment Site
https://www.fisheries.noaa.gov/topic/population-assessments#fish-stocks
NMFS Stock Assessment Improvement Planhttps://www.fisheries.noaa.gov/feature-story/updated-stock-assessment-improvement-plan-builds-past-success
Status of Fisheries and FSSI Quarterly Reports
https://www.fisheries.noaa.gov/national/population-assessments/fishery-stock-status-updates
StockSMART– Explore and Visualize Stock Assessment Results
https://www.st.nmfs.noaa.gov/stocksmart
U.S. Department of Commerce | National Oceanic and Atmospheric Administration | National Marine Fisheries ServicePage 18
Be ready for live discussion and Q & A
on October 21st!
Thank You for Your Attention