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Fisheries Management using a population model

This text explores fisheries management using population models, focusing on the logistic growth equation. It defines key concepts like carrying capacity (K), population dynamics under various birth and death rates, and the implications of harvesting. The relationship between population density, growth rates, and the maximum sustainable yield (MSY) is analyzed. The consequences of fishing practices near MSY, including the risk of entering a 'danger zone' where population recovery becomes difficult, are critically examined. This framework aids in sustainable fisheries practices.

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Fisheries Management using a population model

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  1. Fisheries Management using a population model b<m b=m b>m

  2. Density dependent birth and death Per capita birth,death b=b0-b1B m=m0+m1B b0 Slope=b1 m0 Slope=m1 K is called the carrying capacity K Biomass B

  3. We need to define K in terms of the birth and death rates

  4. Now we need to incorporate K into the population growth model This is called the logistic equation

  5. per capita rate of increase slows down linearly as the biomass increases and reaches 0 when the carrying capacity (K) is reached. • per capita rate of increase reaches an upper limit of r0 as B approaches 0 • It becomes negative when B>K Is called the logistic equation B K

  6. B K/2 K

  7. B K/2 K

  8. What kind of growth curve does this equation generate?—logistic growth

  9. What would happen to a population at K subjected to a harvest rate of C/t C/t B * K/2 K The population would be reduced which would increase dB/dt The decrease would continue until it reaches *where dB/dt increases enough to offset the harvest rate

  10. How great can this harvest rate be and still be compensated for by increased population growth? C/t B * K/2 K Why is called the maximum sustainable yield?

  11. What would happen to a population at K/2 subjected to a harvest rate of B K/2 K is called the Maximum Sustainable Yield (MSY), why?

  12. Constant Quota fishing at levels approaching the MSY shortens the biomass range the population will recover, and the likelihood of entering the danger zone increases. Once the danger zone is entered fishing must stop or be severely curtailed Danger zone Stable biomass range Catch rate B K/2 K Maximum Sustainable Yield (MSY)

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