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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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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
Surplus production = population growth rate Max B∞ = K
Biological turnover rates are a function of Body size (Wmax)
r ≈ P/B ≈ ZThe intrinsic rate of natural increase ≈ Production to biomass ratio ≈ total mortality rate Blueweiss et al. (1978)
r ≈ P/B ≈ Z Modified from Banse & Mosher (1980) Log P/B ratio is a linear function of log body size
Only 2 biological questions in fisheries management • How much? • = Fishing pressure • (effort f) • How? • = Fishing pattern • (catchability q) • (selectivity s)
Fishing mortality = ‘How much’ * ’How’ • Catch = Fishing mortality * Biomass • Catch per unit effort = catchability * Biomass
Number of deaths ti - ti+1 Number caught in interval i Mean number in interval i Thus or Catch equation
All models use a variant of the catch equation • Cohort models (Y/R) • Population models
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
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
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.