Most populations of organisms are too large to actually count all the organisms present. Instead, we make estimations to determine the approximate size of the population.

a) Typically, the area being sampled is divided into a grid.

b) In order to increase the accuracy of the sampling, we use random sampling to sample the population in a predetermined number of grids. The grids are selected randomly either using special computer software or values pre-determined from special population sampling books.

c) We capture as many of the members of the population within each of the grids that have been sampled.

d) We then mark each organism without making them more visible to predators or without harming them.

e) We release each organism back to the location we found it.

f) At a later date, capture as many members of the population found within the same grids sampled in "c" above.

g) Count how many are marked or tagged and how many are unmarked.

h) Use the Lincoln Index to estimate the population size of the organism.