Transcript Overview of Fisheries Assessment

Lecture 8:
Introduction to Stock Assessment
WMAN 445:
Fish Management
Lecture Notes
Fisheries Management Approaches
1.
Manage Fish Populations Directly
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Stocking
Harvest Regulations
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Size limits
Creel limits
Technology limits
Limited Entry
Seasonal Limits
“Special Reg” Areas
Fisheries Management Approaches
2.
Manage the Associated Community
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Food / Prey supplementation
Control Predators / Parasites
Fisheries Management Approaches
3.
Manage Habitats and Water Quality
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Habitat Improvement Structures
Treat pollution / acid precipitation
Bank Stabilization
Artificial Reefs
Limit Activities that Destroy Habitat
(bottom trawls, Dredging)
Fisheries Management Approaches
4.
Manage Activities in the Watershed
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Best Management Practices for
Agriculture and Forestry
Development Planning to minimize
impacts to aquatic systems
Erosion Control
Stormflow Control
Fisheries Management Approaches
1
4
Watershed
Processes
3
Targeted Fish
Species
Aquatic Habitat
and
Water Quality
Aquatic
Communities
2
More
Sustainable
Less
Sustainable
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.
Need for Fisheries Stock
Assessments
Managers must know the answer to
questions such as:
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What is the size of the targeted fish population?
What is the population’s 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?
Some Important Definitions
1.
SPECIES: a group of similar organisms that
can freely interbreed (example: Coho Salmon)
2.
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)
3.
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)
And a Couple More…
4.
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)
5.
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)
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).
What is a Stock Assessment?
Stock Assessment includes:
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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.
Stock Assessment
vs
Fisheries Management
Where does the data come from?
Commercial and / or Recreational Fishery
Catches (Creel Surveys, “Landings”)
• Lots of cheap data
• Biased
Where does the data come from?
Independent Fisheries Surveys (NOAA,
Universities, State Agencies)
• Expensive data
• Unbiased
Stock Assessment in Practice:
What We Measure
Basic Population Parameters
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Fish Abundance
Recruitment
Fishing Mortality
Natural Mortality
Fishing Effort
Surplus Production
Stock Assessment in Practice:
What We Measure
Calculated Yield Functions
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Production Function
Long-Term Potential Yield (LTPY)
Current Potential Yield (CPY)
Recent Average Yield (RAY)
Stock Level Relative to LTPY
Status of Utilization