NUMBAT OER - Open Educational Resources

5. Low rates of recapture

In addition to the assumptions set out in Section 3, the method is vulnerable to low rates of recapture of marked animals. Imagine that 100 animals are captured and marked before release. On the second sampling, a further 100 animals are captured, only one of which is marked. Using the equation above, this suggests a population size of 10 000. If two marked animals had been caught in the second sampling, this would halve the population estimate, whilst three animals would reduce the estimate to 3333. So if the rate of recapture is low, small variations in the number of marked animals in the second sampling will have a profound impact on the estimate of population size.