# Population size

By place

In the Petersen recapture method, catches are considered separately by location and calendar week. Population size N is calculated from two consecutive monitorings A and B: N = n * M / m, where n is the number of individuals and m is the number of recaptures in monitoring B, and M is the number of individuals in monitoring A. For each site, the population size in a given year is calculated as the maximum of all values in that year, and the total population size is calculated as the sum over all sites in that year. If there are no recaptures, the sum of the catches is used. If there is only one monitoring, the number of catches is used.