Lecture 1 review. Why managers cannot avoid making predictions Approaches to prediction Components of population change What is a “population”? How natural populations behave. The ecological basis of sustainable production and harvest.
Nt+1=(SAt+SJt ft)Nt = rtNt where rt=SAt+SJt ft
NtWhat if you plot Nt+1 against Nt, ie if you assume one predictor of next year’s population is this year’s population?
What if your data indicate that the slope doesn’t change, i.e. r is constant or at least independent of Nt?
As you saw in the last tutorial, complete independence of rt from Nt always leads to predictions of exponential increase or decline, never to sustainable N
Age-structured models warn us to expect big drops in mean fecundity and production during both periods of heavy fishing and periods of population recovery
A simulated population decline and recovery, based on yellowfin tuna parameters
Associated changes in surplus production and production/biomass
Biomass next year = Biomass this year + Production – Catch
which implies: Production=Biomass next year-Biomass this year +Catch
There is a long
History of catch
But only a short, history of noisy data on trends in stock size