When presented with a threatened population in need of conservation, the simplest and most basic question a manager can ask is “how big is it?” Unfortunately, this is one of the most challenging questions to answer. Determining the number of individuals in a population is fundamental to effective management. Small, concentrated populations can be destroyed in a single sweep, while large, broadly distributed populations require more resources and complex management involving many stakeholders.
A population that is easy to sample is rare. Animals move – sometimes over enormous distances. Habitats are difficult or impossible to access. Entire popualtions may be adept at avoiding capture. For most populations, it is impossible to count every individual. In marine ecosystems populations can span the entire globe, and the cost of mounting an expedition to systematically sample all members is huge. In order to get accurate estimates of the number of individuals, ecologists have had to devise statistical techniques to estimate the size of a population.