Mark-recapture Technique

• A specific area is demarcated
• A number of individuals are caught, counted and marked, and they are known as the 1st sample
• The marked individuals are released into the environment
• Sufficient time must be allowed for the marked individuals to mix with the rest of the population
• Another group of individuals is caught and counted and they are known as the 2nd sample
• The number of marked individuals in the 2nd sample are counted
• This data is used to determine the estimated size of the population using the following formula:
• This data is used to determine the estimated size of the population using the formula

  P= (m x s) ÷ t

  P= estimated population size

  m= total number of animals captured and marked in 1st sample

  s= total number of animals captured in 2nd sample

  t= number of marked individuals in 2nd sample
• The mark-recapture technique can be improved by repeating the sampling a few times and then calculating an average population size
• Only valid if the marking methods should not injure or damage the organism
• Only valid if the marks are clearly visible for the duration of the investigation
• Only valid if the marking methods do not affect the movement or behaviour of the organism
• Only valid if marked organisms are allowed enough time to mix with the rest of the population before the next sample is taken
• Only valid if the population is closed, so no immigration or emigration take place
• Only valid if the period between the two samplings is sufficiently brief, so that no births or deaths occur