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Unusable Stock

Recruitment. Natural Deaths. Unusable Stock. Disease. Growth. Emigration Immigration. Recruitment. Natural Deaths. Usable Stock. Disease. Growth. Emigration Immigration. Yields. Dynamics of fish stock. Fishing mortality=F. Can be controlled?. R = Recruitment G = Growth

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Unusable Stock

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  1. Recruitment Natural Deaths Unusable Stock Disease Growth Emigration Immigration Recruitment Natural Deaths Usable Stock Disease Growth Emigration Immigration Yields Dynamics of fish stock Fishing mortality=F Dr. Mala Supongpan

  2. Can be controlled? R = Recruitment G = Growth M =Natural mortality F = Fishing mortality HOW? Dr. Mala Supongpan

  3. Dr. Mala Supongpan

  4. Dr. Mala Supongpan

  5. Yield against effort CPUE against effort Analytical methods Holistic methods Dr. Mala Supongpan

  6. Dr. Mala Supongpan

  7. The fish stock assessment needs: • Catches, Species and Sizes composition • Abundance • Biomass estimation • Analytical methods and Holistic methods • Parameter estimation (recruitment, growth, mortality-natural mortality, fishing mortality and total mortality) • Catch and effort data from statistic record (time series) • Population size and catchability • Using catch per unit effort to find original population size and catchability Dr. Mala Supongpan

  8. Parameters for fish stock assessment 1. Length-weight 2. Growth parameter 3. Mortality And data on production Catch and effort, production and biomass Dr. Mala Supongpan

  9. Modal Progression Analysis Dr. Mala Supongpan

  10. Dr. Mala Supongpan

  11. Dr. Mala Supongpan

  12. For virgin stock or limited data 1. Estimation of initial population size and catchability coefficient from the fishing success to catch or effort Original population size (Roughly virgin stock size) Z=M+F Z=M+qf F=qf catchability Leslie’s method Cumulative catch+ DeLury’s method Cumulative effort+ Dr. Mala Supongpan

  13. 2. Estimation of Z using CPUE data 3. Natural mortality estimation When no fishing 4. Fishing mortality estimation F=Z-M Dr. Mala Supongpan

  14. Estimation of total mortality (Z) 1. CPUE data 2. Catch curve based on length composition data 3. Cumulative catch curve based on length composition data 4. Beverton and Holt’s Z equation 5. Plot Z on effort 1. Estimate Z from CPUE data From above equations, then gives: * Dr. Mala Supongpan

  15. Plot Z against effort to estimate F and M Z = M + q*f F = Z - M Dr. Mala Supongpan

  16. Biomass estimation Dr. Mala Supongpan

  17. Swept area to estimate biomass Dr. Mala Supongpan

  18. Dr. Mala Supongpan

  19. Survey strata by depth Dr. Mala Supongpan

  20. Sustainable yield estimation Virgin biomass For conservation, a- should be=0.3 ZB = (F+M)B and the catch Y = FB Dr. Mala Supongpan

  21. Definition Catchability ( ): A fraction of a fish stock which is caught by a defined unit of the fishing effort. When the unit is small enough that it catches only a small part of the stock-0.01 or less-it can be used As an instantaneous rate in computating population change. Also called catchability coeffifient. Dr. Mala Supongpan

  22. Availability: The fraction of a fish population which lives in regions where it is susceptible to fishing during a given fishing season. This fraction receives recruits from or become mingled with the non-available part of the stock at other seasons, or in other years. Dr. Mala Supongpan

  23. Catch per unit of effort (CPUE): The catch of fish, in number or in weight, taken by a defined unit of fishing effort. Also called Catch per effort, fishing success, availability. Dr. Mala Supongpan

  24. Biomass: The weight of a fish stock, or of some defined portion of it. Fishing effort: The total fishing gear in use for a specified period of time. When two or more kinds of gear are used, they must be adjusted to some standard type. Dr. Mala Supongpan

  25. References Gulland, J.A. 1983. Fish stock assessment. (FAO/Wiley series on food and agriculture; v. 1), 223 pp. Ricker, W.E. 1975. Computation and interpretation of biological statistics of fish populations, pp.151-155. Dr. Mala Supongpan

  26. Exercises 1 and 2 Dr. Mala Supongpan

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