Living Marine Resources Cooperative

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The Foundation of Science in Marine Resource
Management and Policy
Michael J. Fogarty NOAA/NMFS/NEFSC
Marine Fisheries Policy Seminar Series
Living Marine Resources Cooperative
Science Center (LMRCSC)
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Topics to be Covered

• Basic Concepts of Population Biology
• The Concept of Biological Production
• Growth
• Maturation
• Mortality
• Recruitment
• Management Strategies and Reference Points
• Control Rules
• Translation and Transmission of Scientific Advice
• Towards Ecosystem Approaches to Fishery Management

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Population Biology Depends on The Development
and Use of Mathematical Models
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You are Used to Seeing Many of the Concepts
ofPopulation Biology in Humans
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• Exponential Growth
• Populations increase proportional to their
  biomass (the rate of change is a function of
  stock size).
• Thomas Malthus (1798) used the exponential growth
  model to project the human population explosion.
• Currently used to model bacterial populations.

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• US Population 1790-2000

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So What Information do we Need?

• Basic Biology
• lifespan
• growth
• maturity rate
• movements
• Fishery Information
• Historical development (areas, gears)
• Past and current regulations (size limits, gear
  restrictions).
• Catch (landings, discards, age/size distribution)
• Effort (catch rates)
• Surveys
• Distribution
• Relative abundance and biomass over time
• Age/size structure
• Life history (growth, maturity)

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Where do we get the Numbers? NEFSC Monitoring
and Observing Program Elements

• Satellite Oceanography
• Oceanographic Buoys/Moorings
• Standardized Research Vessel
• Surveys

• Ships of Opportunity CPR Program
• Observer Program
• Logbooks
• Cooperative Industry Research

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Population Dynamics

• Age Structure
• Reproductive Biology
• Growth
• Mortality
• Recruitment

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The Basic Fish Population Model
dP (G R) (M C)
dP change in population biomass G growth R
recruitment M natural mortality C catch
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Some Definitions
A population is a group of interbreeding
individuals of a species in a particular area
A stock is specified management unit, possibly
corresponding to population but not necessarily so
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Unit Stock
Functions as a management unit
Gulf of Maine Cod Stock
Isolated reproductively
Different growth, spawning areas, maturation
Georges Bank Cod Stock
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Change in Biomass Increases due to Recruitment
Increases due to Individual Growth
- Losses due to Natural
Mortality
- Losses due
to Harvesting
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All these problems require some type of approach
to estimate quantities that are not easily
observed!

• We cannot do a census of everything.
• Its too expensive and also unnecessary!

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Why is fish population dynamics important?

• with population dynamics and models we can
  estimate something we cannot see the number and
  biomass of fish in the sea

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Models of Individual Growth
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Aging Fish
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Atlantic Cod
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How do we age fish?
Use microscope to count annual growth rings
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How long do marine fish live?

• Most in our region live 10-15 years
• Redfish live 25-40 years
• Sand eels live 3-5 years
• Squids live about 1 year

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Age Structure of Fish Populations
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Why do we age fish?

• If you know how many fish were alive at the
  beginning of the year at each age and how many
  have died during the year!
• Then you can estimate fishing rates, biomass
  etc.
• If you know how many new recruits are produced,
  you can predict future catch and biomass.
• We can produce more detailed stock assessments
  and provide better advice.

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• Important points about age structure

Few Ages
Georges Bank Haddock under 2 different fishing
regimes
Heavily fished Lightly Fished
Many Ages
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Growth
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Why is Growth Important?

• The weight gain in fish over time replaces
  biomass removed by fishing!
• Understand the seasonality of the process
• Essential for estimating biomass in the sea

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Why Study Fish Growth?

• We need to know how much fish weigh.
• To estimate the weight of the catch
• To estimate the biomass of fish in the sea

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How do we get fish weights?

• Weigh fish at the port when they are landed
• Weigh fish at sea on commercial or survey vessels
• Estimate the weight from length

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Weight is a cubic function of length wtaL3
A 40 cm YT weighs .511 kg
We can convert length to weight easily

• A 40 cm fish weighs .511 kg

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• We can use curves to describe the growth of fish
  in length and weight

• These relationships fit well and are very useful

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Fish Growth Facts

• Fish Growth is Indeterminate
• Fish grow fast when they are young
• Growth slows with age, but never stops
• Related to food, density, temperature

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Reproductive Biology
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What do we use maturity information for?

• To calculate length and age at first spawning
• To estimate peak spawning times and areas
• To calculate spawner biomass

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Maturation varies by species and region
Maturation is also sensitive to density,
temperature, food resources.
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Mortality
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Mortality Models
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What is it?

• Study of the loss of fish by natural and fishing
  related causes.
• Estimating the rate of decline or the number of
  fish that die during some time period, usually 1
  year.

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Why are mortality rates so important?

• With them
• We can determine the historical size of a stock!
• We can estimate current biomass!
• We can estimate next years biomass!
• We can determine maximum sustainable yields!

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There are many examples of exponential rates that
affect our daily lives!

• The mortgage rate on your house!
• The interest on your 401K retirement plan!
• The life insurance premium you pay to your
  insurance agent!
• Radioactive decay of spent fuel from a nuclear
  power plant!

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An Example of exponential rates Compound
interest on a bank account!
Problem Calculate the size of your bank account
in 13 years with a 5 interest rate if you start
with 1000 dollars now!
You could multiply 1000 X 1.05 for the first
year and 1050 x 1.05 for the second year, and
. For 13 years 1885.65 or you can find the
exponential interest rate and do it the easy way
Iln 1.05.04879 Total 0
x eI x t
Total 1000 x e 0.0487913 1000 x
exp(.04879 x 13) 1885.65
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Mortality Rates for Fish Are Very Much the Same!

• Mortality is a decay process!

Instead of being positive like an interest rate,
it is negative since fish are dying from fishing
or natural causes
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• Total Instantaneous Mortality Z
• How do we calculate this quantity?

• SNt/N0
• Z-ln(S)

• Then S Nt/N0
• 736/1000
• .736
• and Z-ln(S)
• -ln(.736)
• .306

So if you know how many fish were alive at the
beginning of the year, say 1000 and how many are
left at the end of the year, say 736
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• Fishing Mortality Rate

• ZFM

• From Previous page Z.306
• and for most groundfish and flats with M.2
• ZFM
• .306F.2 ,
• .306-.2F
• F.106

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Effects of Different Fishing Rates
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Total Exponential and Annual Mortality Rates
Z
A
These are the equivalent percentage rates
These are total exponential mortality rates
In science jargon we refer to these as
instantaneous rates

• A 1-e-Z

• SNt1/Nt
• Z-lnS

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Mortality Rates Relating the two Types

• Important Points

• Annual Rates are Percentage Rates
• Instantaneous Rates are Exponential Rates
• A Z of 3 an A of 95
• Instantaneous rates are handy because they can be
  added, subtracted, multiplied etc
• Z F M
• Annual rates cannot be manipulated this way

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More on Getting the NumbersVirtual Population
AnalysisSimultaneous Estimation of Fishing
Mortality and Population Size
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Virtual Population Analysis

• Over the lifespan of the 1987 yearclass, 77
  million fish were caught.
• We also know that some fish died from natural
  mortality.
• So, at a minimum, there were 77 million fish when
  they were 1 year olds.
• But this is just the population we saw (the
  virtual population) from the underlying true
  population.
• VPA reconstructs the true population from the
  virtual population.

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VPA

• Reconstruction of all yearclasses gives a total
  population estimate.
• Input Data
• catch at age
• estimate of natural mortality
• initial guess about abundance of survivors at the
  oldest age.

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VPA Calibration

• Initial guesses are replaced with estimates
• oldest age of historical yearclasses estimated by
  assuming that age-7 fish have the same
  vulnerability to the fishery as ages 4-6
• CFxN
• C/FN
• yearclasses that are alive now require more
  information.
• need an independent index of relative abundance
  over time.

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VPA Estimates

• Informative Assessment
• Example SNE yellowtail
• Estimates of stock size and F,
• But also age distribution, recruitment, mature
  biomass, etc.

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Recruitment
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Stock-Recruitment Models
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What is it?

• New fish entering the population from a previous
  years spawning.

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Why is Recruitment Important?

• It is the engine that drives a fishery
• Provides the new fish that sustains the catch in
  the future!
• If we can estimate it we can predict future stock
  status.
• It changes annually based on spawner biomass and
  environmental factors.

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Fluke Recruitment-age 1

• New fish entering the population from a previous
  years spawning
• Different each year, related to spawning stock
  size and environmental factors

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Why is it important to know how much spawning
stock there is?

• Spawning biomass is the equivalent of a fishery
  bank account
• It produces the interest (recruits) for the
  following years.
• Based on current knowledge, more is better!

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Stock-Recruitment
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Why is the Study of Stock-Recruitment So Important

• Used to forecast stock status
• Understand level of spawning biomass necessary to
  produce large sustainable catches
• Calculate key values (reference points) for the
  stock

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Stock-Recruitment Data
Use the data or Fit a curve and use the curve and
its properties.
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Biological Reference Points
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What are Biological Reference Points

• Key fishing rates or biomass levels that are
  related to the maximum potential of a stock
• A fishing rate (F) that produce the highest
  catches or spawning potential
• A biomass level that produces the highest catches
• Produced from relatively simple models
• Yield per recruit, surplus production, SR

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Limit and Target Reference Points
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Target
Management targets are

• A level of F that gets you to a goal.
• An F target gets you to a desired place!
• A level of biomass that is a goal.
• A biomass target is a desired place!

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Limits
Limits are

• Fs you shouldnt exceed, a biomass you shouldnt
  go below
• A key reference point value like Fmsy or Bmsy

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What is overfishing?

• Catching too many fish
• Applying a fishing rate that is too high.
• Result
• The stock cannot produce enough recruits to
  maintain itself at a productive level.

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Why does it matter?

• Causes the stock to decline to a less productive
  state
• Reduces future catches and dollars earned
• Removes fish too early in their life
• Reduces recruitment, in many cases dramatically
• Not sustainable

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Types of Overfishing

• Growth overfishing- related to the size and age
  of fish
• Recruitment overfishing- related to the
  production of new recruits

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Growth Overfishing

• Removing too many young fish
• Size of fish is too small relative to their
  potential

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Examples of Growth Overfishing

• Scallops- were harvested at small sizes for
  decades. Potential was shown when scallops that
  were 4x larger were encountered in closed areas
• Grey sole- discards were very large before the
  nordmore grate was used in the shrimp fishery and
  larger mesh in the groundfish fishery.

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Recruitment Overfishing

• Rate of fishing that reduces stock size to the
  point where recruitment is impaired.
• Removing too many fish so that there are
  insufficient recruits to keep the stock at a
  productive level

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Landings from the Georges Bank haddock fishery
1904-2001
Stock collapsed by the late 1960s
Sustained catch at 45,000 mt
Cost of overfishing over 1 million mt of yield
foregone during 1970-2001
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Surplus Production Models
Production Function
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Populations Cannot Grow Without Limits

• Limited Population Growth
• Logistic growth populations increase
  proportional to their biomass, but the rate of
  increase slows as the population approaches its
  carrying capacity.
• Rate of change (production) is maximum when the
  population is at half of its carrying capacity.

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Production Models

• Grahams Theory of Sustainable Fishing (1935)
• If removals can be replaced by stock production
  each year, the fishery is sustainable.
• If stock size is maintained at half its carrying
  capacity, the population growth rate is fastest,
  and sustainable yield is greatest (Maximum
  Sustainable Yield).

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• Production Models

• Stock Status
• Recent models can use observed yield and multiple
  stock size indices to estimate F and B by
  smoothing and scaling.
• Smoothing stock size estimates are fit to survey
  data using the simple population process
• logistic growth and observed catch.
• More informative than 3-year average.
• Scaling

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Production Models

• Stock Status
• Scaling survey observations are scaled to
  absolute biomass estimates by evaluating the
  response in survey data to absolute removals.
• When catch was not sustainable, stock decreased
  (1970s-1980s).
• When catch was less than potential production,
  stock increased (1960s, 1990s).

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Fit a simple model,estimate parameters, produce
a symetric yield curve (Shaefer), and you get
MSY
Bmsy

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Other Important Reference Points

• Fmax- fishing rate that produces maximum yield
  per recruit
• F0.1- fishing rate that is 1/10 of the slope of
  the Y/R curve at the origin
• F40- fishing rate that gives 40 of the maximum
  spawning potential

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Yield and Spawning Biomass Per Recruit Models
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F0.1
Fmax
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F40
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Biomass Limit
Think of Bmsy as a minimum amount
You dont want to drop below this amount
Bmsy
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F and Biomass Targets
If you fish at Fmsy or below (target) youll get
to Bmsy (target)
Bmsy
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How Do We Prevent Overfishing?

• Limit the number of fish removed!
• Indirect Measures like mesh sizes, area closures,
  time closures, minimum fish sizes.
• Direct Measures like effort limitation, catch
  quotas, individual quotas.

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Control Rules
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What is a Control Rule?

• A roadmap to a goal (higher stock size)!
• Shows you how to get from an undesirable place
  (overfished) to a better place!
• Can be a definition, a graph, or a mathematical
  expression.

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Control Rule
In the context of SFA
Fishing rate limit is Fmsy
Biomass limit is ½ Bmsy
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When is Overfishing Occurring Using Current
Guidelines?
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Overfishing, F too high
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Georges Bank Haddock 1930-1999
Georges Bank Haddock a Long History of overfishing
Overfishing was occurring in every year except
during 1995-1999
We have done real well since 1995!
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When is a Stock Overfished Using Current SFA
Guidlines?
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Overfished, biomass too low, below ½ Bmsy
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Georges Bank Yellowtail Flounder
Overfishing occurred for almost entire history
Biomass was overfished for entire history
Now, low F, recovered biomass, good job!
Dramatic response in recruitment
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Stock Assessment Review Committee (SARC)
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What is the SARC?

• Peer review process to review assessments and
  give advice!
• Review several stock assessments from working
  groups.
• Write an advisory document for the NEFMC and MAFMC

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Assessment Review

• Determine if the fishing rate is too high
• Determine if the biomass is too low.
• Project future biomass under several different
  assumptions

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SARC Products

• Assessment Document
• Advisory Report
• Forecast Stock Status 2 years or more ahead

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Advice

• Suggested actions for controlling or not
  controlling catch.

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SARC What is the point?

• To serve as the interface between scientists and
  managers
• To determine the current status of fish stocks
• To distill stock assessments into a roadmap for
  managers to change or not change current
  conditions.

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The SARC Process
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Closing Thoughts Moving Toward Ecosystem
Approaches to Fisheries
Management
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Single Species Dynamics Reference Points
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Effects of an Environmental Shift
Favorable Environment
Unfavorable Environment
If Intrinsic rate of increase is affected
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• Multispecies Models Technical Interactions

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• Multispecies Models Technical Interactions

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Multispecies Fisheries Biological Interactions
Prey Yield
Prey Fishing Mortality
Predator Fishing Mortality
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Fishing Effects on Carrying Capacity
Standard Model
Habitat Effects Model
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The Challenges Ahead

• Develop Strategies for Consultation with
  Stakeholders
• Choose Specific Management Objectives with
  Stakeholder Input
• Develop Indicators of Ecosystem Status
• Develop Predictive Models of Ecosystem Dynamics
• Develop Precautionary Management Strategies to
  Meet Chosen Objectives