Sustainable exploitation: a review of principles and methods

Although the main theoretical framework determining how to exploit populations was derived almost 50 years ago, overexploitation is common. I review 10 major concepts underlying the regulation of exploitation: population increase can be exploited; density dependence is essential; quantifying density dependence is exceedingly difficult; sustainable exploitation involves reducing population size; population growth rate is usually mismeasured; sustainability has many conflicting definitions and the choice depends upon the objectives; it is better to monitor the population than the harvest; quotas are unstable; increasing effort is simple, reducing it is painful; exploit conservatively. I then give a brief account of each of the nine main methods that are used to determine sustainable exploitation and the uses, advantages and limitations of each. The nine techniques are: surplus production models, yield per recruit models, Robinson and Redford model, linking yield to recruitment and mortality, adjusting to population changes, comparing demography across sites, reducing to a fixed fraction of unexploited population size, full population models and adaptive management.