A more extensive overview of the historical development of capture-recapture analysis is given elsewhere. Briefly, the first use of capture-recapture analysis can be traced back to Graunt who used a similar method for estimating the population of England as early as 16627 and Laplace, who attempted to estimate the population size in France in 1782, but usually it is mentioned that capture-recapture analysis was first applied by Petersen in 1894 for the study of fish populations. He used the so-called two-sample method, the simplest capture-recapture model, to estimate the unknown size of a population of plaice in the Limfjord in Denmark. The first sample provides the animals for marking or tagging and is returned to the population, while the second sample provides the recaptures, i.e. the numbers of animals caught in both samples. Using the number of recaptures and the number of animals caught in the first and the second sample, it is possible, under certain assumptions, to estimate the number not caught in either sample, thus providing an estimate of the total population size. Two-sample capture-recapture analysis was extended to multiple-sample capture-recapture analysis by Schnabel in 1938. Unmarked animals in each sample are given individual (i.e. numbered) marks before being returned to the population, resulting in a known capture history of each marked animal.