1. 2. CRFM - Barbados Summary

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

3. Population growth

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

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

7. r ≈ P/B ≈ Z The intrinsic rate of natural increase ≈ Production to biomass ratio ≈ total mortality rate
Can get a pretty good idea from here how hard we can fish a stock
Blueweiss et al. (1978)

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

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

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

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

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

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

14. 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

15. Options of management B B Y F Y F
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 Y Y F F
MSY, TAC, ITQ, Bag limit
That is all. Any available or conceivable regulation can be reduced to one of the three terms.