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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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Population dynamic models

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





R p b z the intrinsic rate of natural increase production to biomass ratio total mortality rate
r ≈ P/B ≈ ZThe intrinsic rate of natural increase ≈ Production to biomass ratio ≈ total mortality rate

Blueweiss et al. (1978)


R p b z
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
Only 2 biological questions in fisheries management

  • How much?

    • = Fishing pressure

      • (effort f)

  • How?

    • = Fishing pattern

      • (catchability q)

      • (selectivity s)



Catch equation

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
All models use a variant of the catch equation

  • Cohort models (Y/R)

  • Population models


Simple estimators

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
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
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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