1. Lecture 8: Introduction to Stock Assessment
WMAN 445:
Fish Management
Lecture Notes

2. Fisheries Management Approaches
Manage Fish Populations Directly
Stocking
Harvest Regulations
Size limits
Creel limits
Technology limits
Limited Entry
Seasonal Limits
“Special Reg” Areas

3. Fisheries Management Approaches
Manage the Associated Community
Food / Prey supplementation
Control Predators / Parasites

4. 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)

5. 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

6. Fisheries Management Approaches1 3 4
Targeted Fish Species
Aquatic Habitat
and
Water Quality
Watershed Processes
Aquatic Communities 2
More Sustainable
Less Sustainable

7. 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.

8. 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 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?

9. 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)

10. 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)

11. 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).

12. 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.

13. Stock Assessment vs Fisheries Management

14. Where does the data come from?
Commercial and / or Recreational Fishery Catches (Creel Surveys, “Landings”)
Lots of cheap data
Biased

15. Where does the data come from?
Independent Fisheries Surveys (NOAA, Universities, State Agencies)
Expensive data
Unbiased

16. Stock Assessment in Practice: What We Measure
Basic Population Parameters
Fish Abundance
Recruitment
Fishing Mortality
Natural Mortality
Fishing Effort
Surplus Production

17. 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