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Fisheries Management
I. Renewable and Nonrenewable Resources
II. Maximum Sustainable Yield
A. Schaefer Model
B. Beverton-Holt Model
III.Resource Limited Population
IV.Practical and Theoretical Problems
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Renewable and Nonrenewable Resources
I. Geological Resources are Nonrenewable
II. Biological Resources
A. If managed properly, they can be Renewable
B. If managed improperly, they become Nonrenewable
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Renewable and Nonrenewable Resources
Copper
Petroleum
Soils
Dodo
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Renewable and Nonrenewable Resources
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Maximum Sustainable Yield
I. Schaefer ModelRelates Fish Catch to Fishing Effort
II. Beverton-Holt ModelRelates Fish Catch to Fish
Population Dynamics
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Maximum Sustainable Yield
Development of the Concept
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“It took fisheries scientists until the 1930s to prove scientifically that the Victorian scientist T.S. Huxley had been incorrect whenhe said that the great sea fishes were inexhaustible and that itwas futile to try to regulate the great fisheries.”
1. You do not PROVE something scientifically.
2. In hindsight, Huxley could have done better. By the Victorian Era, the Right and Grey Whales had already been wiped out in the North Atlantic.
3. In any case, by mid-century, some people realized that a science-based management of fisheries was necessary.
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Maximum Sustainable Yield:Assumptions Used in its Development
I. Oceanic Ecosystems are Infinitely Resilient
II. It Will be Possible to Accurately Determine Critical Parameters of Fish Populations
III. If a Fish Stock is Overharvested, Fishing Pressure Will Be Reduced
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Maximum Sustainable Yield:Political Context Within Which it Developed
I. Post-War American Domination of the Seas
II. Economic Activities Don’t Require Regulation
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Maximum Sustainable Yield
I. Schaefer ModelRelates Fish Catch to Fishing Effort
II. Beverton-Holt ModelRelates Fish Catch to Fish
Population Dynamics
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Maximum Sustainable Yield
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Maximum Sustainable Yield
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Schaefer Model
Underfishing Overfishing
(hours)
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Schaefer Model
Overfishing Underfishing
(pounds/hour)
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Beverton-Holt Model
F
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Beverton-Holt Model
F
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Beverton-Holt Model
FSchaefer Model
Schaefer Model
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Beverton-Holt Model: Application to a Resource-Limited Population
F
Mortality declines with fishing because:
1. Caught fish don’t die a natural death;
2. A fished population is a younger population, with a lower death rate;
3. Individuals in a fished population have access to more resources, so they are healthier and have a lower death rate.
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Beverton-Holt Model: Application to a Resource-Limited Population
F
Gross Production declines with fishing less rapidly than M declines because:
1. Individuals in a fished population have access to more resources, so they grow faster and have higher fecundity.
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Practical and Theoretical Problems
I. Practical Problems
Determination of Population Parameters(Beverton-Holt Model)
Determination of Fishing Effort(Schaeffer Model)
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OTOLITHS: Information that can be obtained from the
analysis of otolith biomineralization patterns
Age
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OTOLITHS: Information that can be obtained from the
analysis of otolith biomineralization patterns
Spawn Date
Hatch Date
Metamorphosis
Growth History
Age
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For Those Who May Be Interested:
More information on otoliths can be found at
http://www.marinebiodiversity.ca/otolith/english/daily.html
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Population Size: Estimate by Tagging
18,055 herring tagged and released
Subsequent to release, 810,000 fish surveyed
13 tags recovered
(13/810,000) = (18,055/1.12x109)
Population size estimated at 1.12x109 herring
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Determination of Fishing Effort
I. Units used to measure effort must be defined
II. Type of fish-finding technology andfish-harvesting technology must be taken into account
III. “I fish, therefore I lie” must be factored in
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Theoretical Problems
Variable Recruitment
K and r Selection
Stock Stability
Effects of Competitors
Recruitment - Reproduction Time Lag
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Percentage contribution of year classes of Norwegian spring spawn herring to the adult stock from 1954 through 1962. The very good year class of 1950 began first appearing in significant numbers in 1954 and dominated the adult stock throughout this period.
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Resource Mismatch
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Mathematical Modeling of Population Dynamics:
The Logistic Equation
and
r-selected and K-selected populations
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Thomas Malthus:Unlimited Growth
Unlimited Population Growth Based on the Exponential Equation
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Thomas Malthus:Unlimited Growth
Unlimited Population Growth Based on the Exponential Equation
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Limited Population Growth Based on the Logistic Equation
Pierre Francois Verhulst:Limited Growth
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rate of change = ⎟⎠⎞
⎜⎝⎛ −
K
N1rN
The Logistic Equation
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rate of change = ⎟⎠⎞
⎜⎝⎛ −
K
N1rN
The Logistic Equation
N = Population Size
R = Reproductive Capacity of the Species
K = Carrying Capacity of the Ecosystem
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Limited Population Growth Based on the Logistic Equation
Pierre Francois Verhulst:Limited Growth
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Multiple “Steady States” Possible with the Logistic Equation
Pierre Francois Verhulst:Limited Growth
Multiple “Steady States” Possible with the Logistic Equation
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r-selected species K-selected species
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Table 4.2. Characteristics of r-selected and K-selected populations
parameter r-selected K-selected
Environment variable and/or unpredictable
constant and/or predictable
Lifespan short long
Growth rate fast slow
Fecundity high low
Natural mortality high low
Population dynamics unstable stable
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r-selected species K-selected species
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Fishing at 15% of MSY
Fishing at 75% of MSY Fishing at 100% of MSY
Stock Stability
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Strategic Issues
Economics
Maximizing Yield
How to Deal with Catch Variability
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ECONOMICS
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Table 4.3. Example of effect of natural mortality and growth on yield of a year class
Age Number of individuals Weight per individual Yield per recruit
3 1,000,000 15 15.000
4 900,000 17 15.300
5 810,000 19 15.390
6 729,000 21 15.309
7 656,100 23 15.090
8 590,490 25 14.762
MAXIMIZING YIELD PER RECRUIT CLASS
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How to Deal with Catch Variability
The Canadian Cod Example:
Fished to Commercial Extinction BeforeEstablishment of a Moratorium: No Recoveryof the Stock, No Recovery of the Fishery
The Norwegian Cod Example:
Moratorium Established in Response toDeclining Catch: Stock Recovered, as dida Viable Fishery
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HOW MANY FISH SHOULD WE CATCH?
Given the uncertainties involved in estimatingthe maximum sustainable yield; and
Given that the economics of attaining the maximumSustainable yield don’t make sense; and
Given that harvesting the maximum sustainable yieldmakes the population especially prone to collapse;
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Fishing at 15% of MSY
Fishing at 75% of MSY Fishing at 100% of MSY
Stock Stability
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HOW MANY FISH SHOULD WE CATCH?
SUBSTANTIALLY LESS THAN THE
MAXIMUM SUSTAINABLE YIELD!
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Fishing at 15% of MSY
Fishing at 75% of MSY Fishing at 100% of MSY
Stock Stability
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Social Concerns
Information Quality
Natural Var iability