1. Fisheries Management Renewable and Nonrenewable Resources
Maximum Sustainable Yield
A. Schaefer Model
B. Beverton-Holt Model
Resource Limited Population
Practical and Theoretical Problems

2. Renewable and Nonrenewable Resources
Geological Resources are Nonrenewable
Biological Resources
A. If managed properly, they can be Renewable
B. If managed improperly, they become
Nonrenewable

3. Renewable and Nonrenewable Resources
Copper
Petroleum
Soils
Dodo

4. Renewable and Nonrenewable Resources

5. Maximum Sustainable Yield
Schaefer Model
Relates Fish Catch to Fishing Effort
Beverton-Holt Model
Relates Fish Catch to Fish
Population Dynamics

6. Maximum Sustainable Yield
Development of the Concept

8. “It took fisheries scientists until the 1930s to prove scientifically
that the Victorian scientist T.S. Huxley had been incorrect when
he said that the great sea fishes were inexhaustible and that it
was futile to try to regulate the great fisheries.”
You do not PROVE something scientifically.
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.
In any case, by mid-century, some people realized that a science-based
management of fisheries was necessary.

9. Maximum Sustainable Yield: Assumptions Used in its Development
Oceanic Ecosystems are Infinitely Resilient
It Will be Possible to Accurately Determine
Critical Parameters of Fish Populations
III. If a Fish Stock is Overharvested, Fishing
Pressure Will Be Reduced

10. Maximum Sustainable Yield: Political Context Within Which it Developed
Post-War American Domination of the Seas
Economic Activities Don’t Require Regulation

11. Maximum Sustainable Yield
Schaefer Model
Relates Fish Catch to Fishing Effort
Beverton-Holt Model
Relates Fish Catch to Fish
Population Dynamics

12. Maximum Sustainable Yield

13. Maximum Sustainable Yield

14. Schaefer Model
Underfishing
Overfishing
(hours)

15. Schaefer Model
Overfishing
Underfishing
(pounds/hour)

16. Beverton-Holt Model F

17. Beverton-Holt Model F

18. Beverton-Holt Model
Schaefer Model
Schaefer Model F

19. Application to a Resource-Limited Population
Beverton-Holt Model:
Application to a Resource-Limited Population
Mortality declines with
fishing because:
Caught fish don’t die
a natural death;
A fished population is
a younger population,
with a lower death rate;
Individuals in a fished
population have access to
more resources, so
they are healthier and
have a lower death rate. F

20. Application to a Resource-Limited Population
Beverton-Holt Model:
Application to a Resource-Limited Population
Gross Production declines
with fishing less rapidly than
M declines because:
Individuals in a fished
population have access to
more resources, so they
grow faster and have higher
fecundity. F

21. Practical and Theoretical Problems
Practical Problems
Determination of Population Parameters
(Beverton-Holt Model)
Determination of Fishing Effort
(Schaeffer Model)

22. Information that can be obtained from the
OTOLITHS:
Information that can be obtained from the
analysis of otolith biomineralization patterns
Age

23. Information that can be obtained from the
OTOLITHS:
Information that can be obtained from the
analysis of otolith biomineralization patterns
Age
Spawn Date
Hatch Date
Metamorphosis
Growth History

25. For Those Who May Be Interested:
More information on otoliths can be found at
otolith/english/daily.html

26. 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

27. Determination of Fishing Effort
Units used to measure effort must be defined
Type of fish-finding technology and
fish-harvesting technology must
be taken into account
III. “I fish, therefore I lie” must be factored in

28. Theoretical Problems Variable Recruitment K and r Selection
Stock Stability
Effects of Competitors
Recruitment - Reproduction Time Lag

29. Percentage contribution of year classes of Norwegian spring spawn herring to the adult stock from 1954 through The very good year class of 1950 began first appearing in significant numbers in 1954 and dominated the adult stock throughout this period.

30. Resource Mismatch

31. Mathematical Modeling of Population Dynamics:
The Logistic Equation
and
r-selected and K-selected populations

32. Unlimited Population Growth Based on the
Thomas Malthus:
Unlimited Growth
Unlimited Population Growth Based on the
Exponential Equation

33. Unlimited Population Growth Based on the
Thomas Malthus:
Unlimited Growth
Unlimited Population Growth Based on the
Exponential Equation

34. Pierre Francois Verhulst:
Limited Growth
Limited Population Growth Based on the
Logistic Equation

35. The Logistic Equation
rate of change =

36. rate of change = The Logistic Equation N = Population Size
R = Reproductive Capacity of the Species
K = Carrying Capacity of the Ecosystem

37. Pierre Francois Verhulst:
Limited Growth
Limited Population Growth Based on the
Logistic Equation

38. Pierre Francois Verhulst:
Limited Growth
Multiple “Steady States” Possible with the
Logistic Equation
Multiple “Steady States” Possible with the
Logistic Equation

39. r-selected species
K-selected species

40. 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
Population dynamics
unstable
stable

41. r-selected species
K-selected species

42. Stock Stability Fishing at 15% of MSY Fishing at 75% of MSY

43. Strategic Issues Economics Maximizing Yield
How to Deal with Catch Variability

44. ECONOMICS

45. MAXIMIZING YIELD PER RECRUIT CLASS
Table 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

46. How to Deal with Catch Variability
The Canadian Cod Example:
Fished to Commercial Extinction Before
Establishment of a Moratorium: No Recovery
of the Stock, No Recovery of the Fishery
The Norwegian Cod Example:
Moratorium Established in Response to
Declining Catch: Stock Recovered, as did
a Viable Fishery

47. HOW MANY FISH SHOULD WE CATCH?
Given the uncertainties involved in estimating
the maximum sustainable yield; and
Given that the economics of attaining the maximum
Sustainable yield don’t make sense; and
Given that harvesting the maximum sustainable yield
makes the population especially prone to collapse;

48. Stock Stability Fishing at 15% of MSY Fishing at 75% of MSY

49. SUBSTANTIALLY LESS THAN THE MAXIMUM SUSTAINABLE YIELD!
HOW MANY FISH SHOULD WE CATCH?
SUBSTANTIALLY LESS THAN THE
MAXIMUM SUSTAINABLE YIELD!

50. Stock Stability Fishing at 15% of MSY Fishing at 75% of MSY