Part IV. Renewable Resources. Fish – part 1: Biology and optimal harvest Forests Water Biodiversity. B. Fish. Chapter 11. Intro.
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Fish – part 1: Biology and optimal harvest
MSY – max amount harvest year after year in a sustainable fashion. Exploitation beyond MSY leads to declining populations.
Initially, there is no growth, then over some range of population (up to X2), population growth is increasing. Beyond X2, the growth of the population is decreasing.
The logistic growth function represented in Figure 11.1 represents a compensated growth function (growth rate always declining).
11.2 represents a depensated growth function, where the growth rate initially increases and then decreases.
Fig.11.3 contains a critically depensated growth function where, X0 represents the minimum viable population. If population falls below this level, growth becomes negative and population becomes irreversibly headed towards 0.
Figure 11.6 illustrates a set of yield functions, where each curve represents a different level of fishing effort.
Of course, not every point on each yield function is sustainable (growth = catch)
Superimposed equilibrium catch function on the yield functions – gives sustainable yields (catch=growth) at C1, C2, C3
The 1 point of sustainable catch associated with each level of effort is graphed with the corresponding level of effort on the x axis
As effort increases, sustainable yield increases and then decreases. Note order of C1, C2, C3.
The objective of fishery management would be to choose a point along the sustainable catch curve that maximizes the sum of economic rent + consumer + producer surplus.
The result is that the locus of points that illustrate the biological equilibrium associated with different supply functions has shifted inward (Figure 11.7).