Lecture 8: Introduction to Stock Assessment

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Lecture 8Introduction to Stock Assessment

• WMAN 445
• Fish Management
• Lecture Notes

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Fisheries Management Approaches

• Manage Fish Populations Directly
• Stocking
• Harvest Regulations
• Size limits
• Creel limits
• Technology limits
• Limited Entry
• Seasonal Limits
• Special Reg Areas

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Fisheries Management Approaches

• Manage the Associated Community
• Food / Prey supplementation
• Control Predators / Parasites

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Fisheries Management Approaches

• Manage Habitats and Water Quality
• Habitat Improvement Structures
• Treat pollution / acid precipitation
• Bank Stabilization
• Artificial Reefs
• Limit Activities that Destroy Habitat (bottom
  trawls, Dredging)

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Fisheries Management Approaches

• Manage Activities in the Watershed
• Best Management Practices for Agriculture and
  Forestry
• Development Planning to minimize impacts to
  aquatic systems
• Erosion Control
• Stormflow Control

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Fisheries Management Approaches
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3
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Targeted Fish Species
Aquatic Habitat and Water Quality
Watershed Processes
Aquatic Communities
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More Sustainable
Less Sustainable
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Need for Fisheries Stock Assessments

• All fish management approaches require
  quantitative information on the status of the
  fishery and factors that influence, have
  influenced, or are likely to influence that
  status.

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Need for Fisheries Stock Assessments

• Managers must know the answer to questions such
  as
• What is the size of the targeted fish population?
• What is the populations age structure?
• What is the reproductive capacity of the
  population?
• How many fish can be harvested each year? Which
  sizes should be left alone?
• Which habitat or water quality conditions
  influence the population?
• Do interactions with other species affect the
  population?
• Which human activities other than fishing affect
  the fishery?

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Some Important Definitions

• SPECIES a group of similar organisms that can
  freely interbreed (example Coho Salmon)
• POPULATION a group of individuals of the same
  species that have a high probability of
  interacting with each other and interbreeding
  (example Upper Snake River Coho Salmon)
• STOCK a harvested or managed unit of fish (may
  include more than one population or species)
  (example Pacific Northwest Salmon off Oregon and
  Washington Coast)

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And a Couple More

• SUBSPECIES taxonomically distinct individuals
  that occupy non-overlapping geographical ranges,
  but share the essential characteristics of the
  species such as interbreeding (example
  Yellowstone Cutthroat Trout, Southern Appalachian
  Brook Trout)
• EVOLUTIONARILY SIGNIFICANT UNIT (ESU) a
  geographically isolated portion of the species
  population has high level of genetic difference
  from other subpopulations of the species, but not
  recognized taxonomically as a separate subspecies
  or species (California Coho Salmon)

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What is a Stock Assessment?

• The use of statistical and mathematical
  calculations to make quantitative predictions
  about the response of fish populations to
  alternative management choices (usually
  alternative harvest levels).

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What is a Stock Assessment?

• Stock Assessment includes
• Estimate of current population size.
• Estimate of current harvest rate.
• Estimates of population size or harvest rates at
  which the stock can be maintained over time.
• Predictions of population dynamics under various
  management scenarios.

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Stock Assessment vsFisheries Management
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Where does the data come from?

• Commercial and / or Recreational Fishery Catches
  (Creel Surveys, Landings)
• Lots of cheap data
• Biased

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Where does the data come from?

• Independent Fisheries Surveys (NOAA,
  Universities, State Agencies)
• Expensive data
• Unbiased

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Stock Assessment in Practice What We Measure

• Basic Population Parameters
• Fish Abundance
• Recruitment
• Fishing Mortality
• Natural Mortality
• Fishing Effort
• Surplus Production

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Stock Assessment in Practice What We Measure

• Calculated Yield Functions
• Production Function
• Long-Term Potential Yield (LTPY)
• Current Potential Yield (CPY)
• Recent Average Yield (RAY)
• Stock Level Relative to LTPY
• Status of Utilization