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Lecture 8: Introduction to Stock Assessment

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

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  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 Approaches 1 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 vsFisheries 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

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