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

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

Renewable and Nonrenewable Resources

Copper

Petroleum

Soils

Dodo

Renewable and Nonrenewable Resources

Maximum Sustainable Yield

I. Schaefer ModelRelates Fish Catch to Fishing Effort

II. Beverton-Holt ModelRelates Fish Catch to Fish

Population Dynamics

Maximum Sustainable Yield

Development of the Concept

“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.

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

Maximum Sustainable Yield:Political Context Within Which it Developed

I. Post-War American Domination of the Seas

II. Economic Activities Don’t Require Regulation

Maximum Sustainable Yield

I. Schaefer ModelRelates Fish Catch to Fishing Effort

II. Beverton-Holt ModelRelates Fish Catch to Fish

Population Dynamics

Maximum Sustainable Yield

Maximum Sustainable Yield

Schaefer Model

Underfishing Overfishing

(hours)

Schaefer Model

Overfishing Underfishing

(pounds/hour)

Beverton-Holt Model

F

Beverton-Holt Model

F

Beverton-Holt Model

FSchaefer Model

Schaefer Model

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.

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.

Practical and Theoretical Problems

I. Practical Problems

Determination of Population Parameters(Beverton-Holt Model)

Determination of Fishing Effort(Schaeffer Model)

OTOLITHS: Information that can be obtained from the

analysis of otolith biomineralization patterns

Age

OTOLITHS: Information that can be obtained from the

analysis of otolith biomineralization patterns

Spawn Date

Hatch Date

Metamorphosis

Growth History

Age

For Those Who May Be Interested:

More information on otoliths can be found at

http://www.marinebiodiversity.ca/otolith/english/daily.html

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

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

Theoretical Problems

Variable Recruitment

K and r Selection

Stock Stability

Effects of Competitors

Recruitment - Reproduction Time Lag

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.

Resource Mismatch

Mathematical Modeling of Population Dynamics:

The Logistic Equation

and

r-selected and K-selected populations

Thomas Malthus:Unlimited Growth

Unlimited Population Growth Based on the Exponential Equation

Thomas Malthus:Unlimited Growth

Unlimited Population Growth Based on the Exponential Equation

Limited Population Growth Based on the Logistic Equation

Pierre Francois Verhulst:Limited Growth

rate of change = ⎟⎠⎞

⎜⎝⎛ −

K

N1rN

The Logistic Equation

rate of change = ⎟⎠⎞

⎜⎝⎛ −

K

N1rN

The Logistic Equation

N = Population Size

R = Reproductive Capacity of the Species

K = Carrying Capacity of the Ecosystem

Limited Population Growth Based on the Logistic Equation

Pierre Francois Verhulst:Limited Growth

Multiple “Steady States” Possible with the Logistic Equation

Pierre Francois Verhulst:Limited Growth

Multiple “Steady States” Possible with the Logistic Equation

r-selected species K-selected species

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

r-selected species K-selected species

Fishing at 15% of MSY

Fishing at 75% of MSY Fishing at 100% of MSY

Stock Stability

Strategic Issues

Economics

Maximizing Yield

How to Deal with Catch Variability

ECONOMICS

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

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

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;

Fishing at 15% of MSY

Fishing at 75% of MSY Fishing at 100% of MSY

Stock Stability

HOW MANY FISH SHOULD WE CATCH?

SUBSTANTIALLY LESS THAN THE

MAXIMUM SUSTAINABLE YIELD!

Fishing at 15% of MSY

Fishing at 75% of MSY Fishing at 100% of MSY

Stock Stability

Social Concerns

Information Quality

Natural Var iability