Capture-recapture sampling (also referred to as “capture-mark-recapture sampling” or “mark-release-recapture sampling”) is a method used to estimate the unknown size of a population. In practice, it is often not feasible to manually count every individual element in a population because of time, budget, or other constraints. And, in many situations, capture-recapture sampling can produce a statistically valid estimate of a population size in a more efficient and timely manner than a census.

The most basic application of capture-recapture sampling consists of two stages. The first stage involves drawing (or capturing) a random sample of elements from a population of unknown size, for example, fish in a pond. The sampled elements are then marked, or tagged, and released back into the population. The second stage consists of ...