Overexploitation

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Overexploitation
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What?

• Hunting
• Logging
• Non-timber forest products (fruits, nuts,
  medicinal plants, etc)
• Fishing

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Overexploitation
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Two types of impact

• Impact on target species.
• Impact on non-target species.

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Impacts on target species

• Selective hunting, fishing, logging and other
  exploting activities directed towards a target
  species.
• This is called direct targeting.
• Removal of species or reproductive units of
  species (seeds, nuts, etc).
• Simplification of ecosystems.

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Impacts on non-target species

• Species taken accidentally or opportunistically.
• Species deprived of their food.
• Species deprived of their habitat.
• Change in environmental conditions, like amount
  of light and shadow.
• Loss of functional species, ecosystem engineer.

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Sustainable exploitation
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Biolgical theory of sustainable exploitation

• Constant quota exploitationThe numbers removed
  are constant. MSY (maximum sustainable yield).
• Constant effort (Proportional exploitation)A
  constant effort, like number of days hunting or
  fishing. Explotiation effort proportional to the
  population size.
• Threshold exploitationThe use of treshold to
  determine not only the rate of exploitation but
  also wether exploitation should take place at
  all. To only take the surplus.

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Bioeconomics

• We need to look at and understand economics if we
  want to achieve sustainable yield.
• Bioeconomic models.
• Look at incentives and disincentives.

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Open access tragedy of the commons

• If there is open access there is a higher
  probability of overexploitation.
• In fear of your self-restraint being exploited by
  someone else you do not restrain yourself to the
  degree you should.

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Discounting

• The phenomenon of exploiting heavily now, rather
  than conserving for the future.
• You might be uncertain about your rights in the
  future.
• It might even be more economically rational to
  put the money in the bank.

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Calculation of sustainable yield

• Surplus yield (production)If you know how yields
  have responded to different levels of
  exploitation effort over time, you estimate the
  dome-shaped yield curve. Has several pitfalls if
  your curve is not correct.
• Yield per recruitThe level of mortality that
  maximize the yield under the tradeoff between
  numbers and value.
• Full demographyFull-blown population models with
  stochasticity aid in deciding a sustainable
  yield.

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The demographic rules of thumb to models

• Models are useless if we lack data and go on to
  guessing the parameters.
• The most vulnerable species are often the ones we
  know the least about.
• A model is a simplification of reality.
• Always be critical to your model, and take care
  to identify its weaknesses.

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Sustainable use and biodiversity

• The goal is sustainable use and maintainance of
  biodiversity.
• Even well-meaning management prescriptions can be
  misguided and lead species to extinction.
• Important to recognize management and sustainble
  yield as a part of conservation.
• Work in other areas than just that of scientific
  biology economics, institutional issues,
  management, sociology, etc.