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2. CRFM - Barbados Summary

2. CRFM - Barbados Summary. Multispecies. Predation. Predation. R. M. Z. r. F. G. Population dynamic models. Stock B. Environment. Fishing. Management. Climate. 2 kind of models: Individually based models Population models. Population growth.

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2. CRFM - Barbados Summary

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  1. 2. CRFM - BarbadosSummary

  2. Multispecies Predation Predation R M Z r F G Population dynamic models Stock B Environment Fishing Management Climate • 2 kind of models: • Individually based models • Population models

  3. Population growth

  4. Surplus production = population growth rate Max B∞ = K

  5. Biological turnover rates are a function of Body size (Wmax)

  6. r ≈ P/B ≈ ZThe intrinsic rate of natural increase ≈ Production to biomass ratio ≈ total mortality rate Blueweiss et al. (1978)

  7. r ≈ P/B ≈ Z Modified from Banse & Mosher (1980) Log P/B ratio is a linear function of log body size

  8. Only 2 biological questions in fisheries management • How much? • = Fishing pressure • (effort f) • How? • = Fishing pattern • (catchability q) • (selectivity s)

  9. Fishing mortality = ‘How much’ * ’How’ • Catch = Fishing mortality * Biomass • Catch per unit effort = catchability * Biomass

  10. Number of deaths ti - ti+1 Number caught in interval i Mean number in interval i Thus or Catch equation

  11. All models use a variant of the catch equation • Cohort models (Y/R) • Population models

  12. Production if F = M The exploitation rate (E) is Gulland’s estimator for unfished stocks: Cadima’s estimator for fished stocks: Multispecies: Jeppe’s estimator for fished stocks: Simple estimators Catch

  13. We do not always need a model • If information is available on biomass and catch in a corresponding area then • Estimate Z from catch-curve or from r as and

  14. Options of management BMSY, Minimum SSB, MBAL, Bpa Stocking, Bio-manipulation, Enhancement B B Size of capture: tc Mortality index: Z=F+M Exploitation rate: E = F/Z Effort control: f = F/q F control: F0.1, Fmed etc. Closed area Closed season F Y Y F MSY, TAC, ITQ, Bag limit That is all. Any available or conceivable regulation can be reduced to one of the three terms.

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