Natural Resource BiometricsMark and Recapture MethodsPetersons Method: (Single marking)The Peterson method is the simplest mark and recapture method. The procedure involves capturing a number of individuals, marking, releasing, and then recapturing to check for marked individuals. All of this needs to be done over a relatively short period of time. The second sample needs to be random and allow for the unmarked individuals to have the same opportunity to be captured. The Biased Estimator Equation:
The variables are:
This formula is widely used because it is intuitively clear. But the formula can produce a biased population estimate. If (M + C) is greater than or equal to N and at least 7 recaptures R > 7 this formula can be used. This formula considers that once an individual is counted it is not replaced back into the population. Thus eliminating the possibility of sampling the same individual twice.
The Unbiased Estimator Equation:
If removing sampled individuals is not feasible, a second formula can be used. The Unbiased Estimator Equation (replacement accounted for):
Five assumptions to be considered for an accurate estimate when using the corrected formulas:
Other considerations:
Also See: Chapter 2  Estimating Abundance: MarkandRecapture pages 1627 in:

Natural Resources Biometrics by David R. Larsen is licensed under a Creative Commons AttributionShareAlike 4.0 International License . Author: Shane Rice and Dr David R. Larsen Created: October 11, 1995 Last Updated: Ocotber 13, 2014 