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Introduction to Stock Assessment and Management

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Discuss possible objectives of fisheries management and their ... walleye. whitefish. Northern Cod Fishery. Trends in Cod Abundance. Trends in Cod Catch Rates ... – PowerPoint PPT presentation

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Title: Introduction to Stock Assessment and Management


1
Introduction to Stock Assessment and Management
2
Definition of Stock Assessment
Stock assessment is the quantitative prediction
of the reaction of fish populations to
alternative management actions. - paraphrased
from H W, p. 3
3
Definition of Fisheries Management
Fisheries Management is the application of
regulations and/or enhancement in a fishery in
order to sustain both fish stocks and the fishing
industry. - paraphrased from H W, p. 3
  • Good stock assessment
  • summarizes biological information
  • not all information of equal value
  • assists managers in choosing among
  • alternative management actions

4
Stages in the Development of a Fishery
5
Some Examples of Fisheries Development
  • Atlantic
  • Cod
  • Pacific
  • herring
  • Lake Winnipeg
  • sauger
  • walleye
  • whitefish

6
Northern Cod Fishery
7
Trends in Cod Abundance
8
Trends in Cod Catch Rates
9
Trends in Pacific Herring
10
Pacific Herring
11
Manitoban Fisheries
12
Catch Trends in Lake Winnipeg
13
Objectives of Fisheries Management
What/Who benefits from good management?
  • Objectives
  • Biological
  • Economic
  • Recreational
  • Social

14
Biological Objectives
Sustainable Harvest (i.e. avoid local extinction)
other considerations
  • MSY
  • fish highly variable
  • single MSY unrealistic
  • arbitrary safety margin
  • e.g. F0.1
  • maybe too little

15
Economic Objectives
  • Maximize net profits (no pun)
  • a.k.a. resource rent
  • value minus cost

Note only variable costs shown
16
Social Objectives
  • may focus on subjective issues
  • self image of fishers
  • cultural preservation
  • may be economically inefficient
  • Attempt to measure as
  • number of jobs
  • settlement patterns
  • income distribution
  • among individuals
  • among communities

An uneasy mix of traditional attitudes and
technological innovation
17
Recreational Objectives
  • What is important to fishers?
  • number of fish caught
  • size of fish caught (trophies)
  • time spent fishing

Managers may attempt to maximize one of these.
18
Decisions and Risk
Do you prefer A) 50 B) 100 if I flip
heads C) either A or B
Classification of Strategies
Preference Type A Risk
Averse B Risk Prone C Risk Neutral
19
Which Strategy Would You Choose?
A50_at_100 B100_at_50 Ceither
  • You owe 25 on your boat
  • You owe 75 on your boat
  • You owe nothing on your boat
  • You owe nothing on your boat but have a fuel
    and food bill of 35
  • You owe 150 on your boat

20
Discounting and Resource Management
What should you do to maximize profits?
21
Does Discounting Make Sense?
  • What is the value of letting one more fish breed?
  • without discounting, it is infinite when
    summed over all time
  • Discounting Captures
  • alternative investments (opportunity costs)
  • uncertainty about the future
  • Discounting Ignores
  • non-monetary or unquantified objectives

22
Multiple Objectives
So how can a manager use this?
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