The mark-capture-release method is used for mobile organisms as opposed to plants. It’s popular for estimating the size of an animal population. A portion of the organism under investigation is caught then marked before being released back into the community. Later the same is done again and the number of marked animals is counted separately.

Due to the fact that the marked individuals taken the second time round should be proportional to the total number of marked individuals within the whole population, an estimate of the population can be calculated using the Lincoln-Petersen Index:

N = S₁S₂

R

Where N is the population, S₁ is the first sample, S₂ is the second sample, and R is the recaptures.

Points that should be taken into consideration when using this method are:

• the markings used should not affect the behaviour of the organism
• the population must not change during the study e.g. through death, birth or migration
• the marked organism must be allowed to mix back into its population

This is still only a very rough estimate of what the true population is and any answer will usually be in the range of N