Artificial Population Regulation n For regulation of populations n For commercial harvest n Maximum...
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Artificial Population Regulation
For regulation of populations For commercial harvest
Maximum Sustained Yield (MSY)– Based on the logistic equation:
dN/dt = rN((K-N)/K)
– Generally found at 1/2 the carrying capacity (K)– Formula for MSY
H = (Kr)/4
Optimum yield
Below MSY because of other interests Defined in the U.S. Fishery Conservation and
Management Act of 1976– “the quantity . . . (1) that will provide the greatest
overall benefit to the nation, with reference to food production and recreation and
– (2) that is prescribed as such on the basis of maximum sustained yield as modified by any relevant economic, social, or ecological factors.
Reproduction curves & replacement
K type populationsr populations
45o line is density independent replacement level
Haddock & Cod fisheries
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Fixed effort harvesting
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Multiple equilibria in harvesting
Eo would harvest to extinctionU= unstable equilibrium
Declining harvest efficiency with increased density
IFQ’s
Individual fishing quota– Allowable catch divided into %’s awarded to or
purchased by fisherman and companies Avoids “fishing derby” Can be sold or traded High cost excludes many fishermen
– Can be overcome if community quotas are allowed
Dynamic pool example
Plaice (Krebs, Fig. 17.5)
Best harvest rate would have been about 1/2 of actual level
Biological Conservation
Population viability analysis (PVA)– How vulnerable to extinction? Includes minimum
viable population (MVP) Three general methods
– Long term studies - biogeographical patterns– Subjective expert assessment– General mathematical model
Simulation models seem to hold the most promise
Problems with the analysis:– Changing conditions– Stochastic forces
Causes of rarity
Habitable areas are:– Short-lived– Small– Isolated
Resources sparse Predators Genetic variation lacking
Florida pantherInput demographic patterns Simulation results
Initiation Probability of extinction (years)
Age of reproduction
Adult mortality
Litter size N K 25 50 100 200
Mean time to extinction
3 25 3.0 45 45 0.24 0.77 1.00 1.00 39
3 25 2.5 45 45 0.38 0.94 1.00 1.00 30
3 20 3.0 45 45 0.04 0.28 0.95 0.95 77
3 20 2.5 45 45 0.11 0.57 1.00 1.00 51
2 25 3.0 45 45 0.04 0.45 0.77 0.77 96
2 25 2.5 45 45 0.11 0.91 0.99 0.99 56
2 20 3.0 45 45 0.00 0.04 0.11 0.11 114
2 20 2.5 45 45 0.01 0.27 0.56 0.56 107