fisheries management t review of maximum sustainable yield concepts and problems

Fisheries Management

TReview of Maximum Sustainable Yield Concepts and Problems

Reasons to Fish Below the MSY

I. Inaccurate Information

A. I Fish Therefore I Lie (Schaefer Model)

B. Not Enough Biological Data (Beverton-Holt Model)

II. Variable Recruitment

III. Resource Mismatch

IV. Presence of Competitors

V. Stock Stability

VI. Economics (Law of Diminishing Returns)I. T

Reasons to Fish Below the MSY

I. Inaccurate Information

A. I Fish Therefore I Lie (Schaefer Model)

B. Not Enough Biological Data (Beverton-Holt Model)

II. Variable Recruitment

III. Resource Mismatch

IV. Presence of Competitors

V. Stock Stability

VI. Economics (Law of Diminishing Returns)I. T

Schaefer Model

Underfishing Overfishing

(hours)

Schaeffer Model

Requirements:

Measurement of Fish Caught

Measurement of Fishing Effort

Schaeffer Model

Fish Caught per Unit of Fishing Effort:

A PROXY for Population Size

Schaefer Model

Overfishing Underfishing

(pounds/hour)

Beverton-Holt Model

Requirements:

Measurement of Fish Caught

Knowledge of Fish Biology

Population Size (Tagging)

Age (Otoliths)

Reproductive Biology

Beverton-Holt Model

F

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.

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.

Reasons to Fish Below the MSY

I. Inaccurate Information

A. I Fish Therefore I Lie (Schaefer Model)

B. Not Enough Biological Data (Beverton-Holt Model)

II. Variable Recruitment

III. Resource Mismatch

IV. Presence of Competitors

V. Stock Stability

VI. Economics (Law of Diminishing Returns)I. T

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.

INITIAL DEPOSIT 10,000$ INITIAL DEPOSIT 10,000$ INTEREST RATE 10%/YR INTEREST RATE 10%/YR (AVG)I/R CONDITION CONSTANT I/R CONDITION FLUCTUATING WITHDRAWL AMT 1000 WITHDRAWL AMT 1000W/D CONDITION CONSTANT W/D CONDITION CONSTANT

YEB- YEB- YEB- YEB-YEAR BW/D W/D AMT AW/D YEAR BW/D W/D AMT AW/D

10000 100000 11000 1000 10000 0 10500 1000 95001 11000 1000 10000 1 10450 1000 94502 11000 1000 10000 2 9639 1000 86393 11000 1000 10000 3 9503 1000 85034 11000 1000 10000 4 9353 1000 83535 11000 1000 10000 5 8938 1000 79386 11000 1000 10000 6 8732 1000 77327 11000 1000 10000 7 8505 1000 75058 11000 1000 10000 8 8631 1000 76319 11000 1000 10000 9 8241 1000 7241

10 11000 1000 10000 10 8182 1000 7182

INITIAL DEPOSIT 10,000$ INITIAL DEPOSIT 10,000$ INTEREST RATE 10%/YR INTEREST RATE 10%/YR (AVG)I/R CONDITION CONSTANT I/R CONDITION FLUCTUATING WITHDRAWL AMT 1000 WITHDRAWL AMT 1000W/D CONDITION CONSTANT W/D CONDITION CONSTANT

YEB- YEB- YEB- YEB-YEAR BW/D W/D AMT AW/D YEAR BW/D W/D AMT AW/D

10000 100000 11000 1000 10000 0 10500 1000 95001 11000 1000 10000 1 10450 1000 94502 11000 1000 10000 2 9639 1000 86393 11000 1000 10000 3 9503 1000 85034 11000 1000 10000 4 9353 1000 83535 11000 1000 10000 5 8938 1000 79386 11000 1000 10000 6 8732 1000 77327 11000 1000 10000 7 8505 1000 75058 11000 1000 10000 8 8631 1000 76319 11000 1000 10000 9 8241 1000 7241

10 11000 1000 10000 10 8182 1000 7182

INITIAL DEPOSIT 10,000$ INITIAL DEPOSIT 10,000$ INTEREST RATE 10%/YR INTEREST RATE 10%/YR (AVG)I/R CONDITION CONSTANT I/R CONDITION FLUCTUATING WITHDRAWL AMT 1000 WITHDRAWL AMT 1000W/D CONDITION CONSTANT W/D CONDITION CONSTANT

YEB- YEB- YEB- YEB-YEAR BW/D W/D AMT AW/D YEAR BW/D W/D AMT AW/D

10000 100000 11000 1000 10000 0 10500 1000 95001 11000 1000 10000 1 10450 1000 94502 11000 1000 10000 2 9639 1000 86393 11000 1000 10000 3 9503 1000 85034 11000 1000 10000 4 9353 1000 83535 11000 1000 10000 5 8938 1000 79386 11000 1000 10000 6 8732 1000 77327 11000 1000 10000 7 8505 1000 75058 11000 1000 10000 8 8631 1000 76319 11000 1000 10000 9 8241 1000 7241

10 11000 1000 10000 10 8182 1000 7182

Reasons to Fish Below the MSY

I. Inaccurate Information

A. I Fish Therefore I Lie (Schaefer Model)

B. Not Enough Biological Data (Beverton-Holt Model)

II. Variable Recruitment

III. Resource Mismatch

IV. Presence of Competitors

V. Stock Stability

VI. Economics (Law of Diminishing Returns)I. T

Reasons to Fish Below the MSY

I. Inaccurate Information

A. I Fish Therefore I Lie (Schaefer Model)

B. Not Enough Biological Data (Beverton-Holt Model)

II. Variable Recruitment

III. Resource Mismatch

IV. Presence of Competitors

V. Stock Stability

VI. Economics (Law of Diminishing Returns)I. T

Reasons to Fish Below the MSY

I. Inaccurate Information

A. I Fish Therefore I Lie (Schaefer Model)

B. Not Enough Biological Data (Beverton-Holt Model)

II. Variable Recruitment

III. Resource Mismatch

IV. Presence of Competitors

V. Stock Stability

VI. Economics (Law of Diminishing Returns)I. T

Fishing at 15% of MSY

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

Stock Stability(Population Resilience)

Stock Size

Stock Size

Fishing

Stock SizeGood Recruitment

Stock SizeGood Recruitment

Stock SizeBad Recruitment

Stock SizeBad Recruitment

Stock SizeLow Stock Size

Stock SizeLow Stock Size

Stock SizeENSO

Stock SizeENSO

Stock SizeLow Stock Size High Stock Size

Stock Size

Low Stock Size High Stock Size

Stock Size

Low Stock Size High Stock Size

Fishing at 15% of MSY

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

Reasons to Fish Below the MSY

I. Inaccurate Information

A. I Fish Therefore I Lie (Schaefer Model)

B. Not Enough Biological Data (Beverton-Holt Model)

II. Variable Recruitment

III. Resource Mismatch

IV. Presence of Competitors

V. Stock Stability

VI. Economics (Law of Diminishing Returns)I. T

ECONOMICS

The Canadian Cod Example:

Fished to Commercial Extinction BeforeEstablishment of a Moratorium: No Recoveryof the Stock, No Recovery of the Fishery

During the 1980s cod catches remained steady but that was because larger, more powerful and sophisticated vessels were chasing the fewremaining fish.

During the 1980s cod catches remained steady but that was because larger, more powerful and sophisticated vessels were chasing the fewremaining fish.

Working harder and harder, to catch the few remaining cod.

"In normal years we'd get 200,000 pounds of cod, but that year it was more like 70,000 pounds. Then all of a sudden they just crashed."

Fisheries scientists concluded that quotas had to be more than halved in order to prevent this stock's collapse. Politicians were appalled; the proposed quotas would have caused economic chaos throughout Eastern Canada.

So the politicians compromised what could not be compromised. Quotas were cut by only 10 percent.

Fishermen tried as hard as they could, but could only catch 122,000 of the 190,000-ton cod quota for 1991.

The estimated combined weight of the adult cod population was a mere 1.1 percent of its historic levels of the early 1960s.

ECONOMICSLaw of Diminishing Returns

Social Concerns

Information Quality

Natural Var iability

Reasons to Fish Below the MSY

I. Inaccurate Information

A. I Fish Therefore I Lie (Schaefer Model)

B. Not Enough Biological Data (Beverton-Holt Model)

II. Variable Recruitment

III. Resource Mismatch

IV. Presence of Competitors

V. Stock Stability

VI. Economics (Law of Diminishing Returns)I. T