How do scientist estimate the population of the Beluga whale?

What are the various scientific methods that we can use to estimate the number of individuals in a population?

We will study one of the method today which is called the mark/ recapture method.

The mark/recapture method depends on catching a number of individuals from a population, marking them in some way (e.g. with coloured leg bands for birds) and releasing them. Then a second portion of the population is captured. The whole populations size can be estimated by the formula:
P = N x M/R

where P = estimated population size
M = number of individuals marked during first capture
N = total number of individuals (marked and unmarked) captured second time
R = number of marked individuals captured second time

This estimate of population size is called the Lincoln Index.
  1. There are some assumptions behind this equation. What do you think are some of the assumptions?
  2. There are also a number of technical difficulties involved in this method of estimating population sizes. What are they?

PAUSE! Lets talk share this in class.

Find a partner to carry out the experiment below.

  1. Two different coloured beans
  2. bag

  1. Collect a fistful of yellow beans in any manner you like e.g. grab some without looking.
  2. Count all of these beans and put them aside.
  3. Replace the yellow beans taken with an identical number of black beans. These different coloured beans represent the “marked” population.
  4. To simulate homogeneous mixing of marked and unmarked organisms, shake the container until all the beans are thoroughly mixed.
  5. Now collect a fistful of second sample without looking into the container. Count as required.
  6. Calculate the population size using the formula given above. How close is it to the actual number of beans you have in your container?
  7. Tabulate your result as individual pair and as a class. Is the individual pair result closer to the population size or the total class result?
  8. Upload you class data here for all.


Analysis of data:
  1. Study the data from all groups and your group. Did the Lincoln index estimation of the population from most group an over estimation or under estimation of the actual population?
  2. Is there any correlation between the size of the initial marked sample and the accuracy of the estimation of the population size?
  3. What is the percentage of error for most groups?
  4. Is there any group's result that you will not include in your group collation? Why?
  5. Why was teh total of all the groups taken instead of the average?

  1. Suggest ways to improve on this simulation.
  2. Name as many different marked methods as you can.
  3. Identify two field conditions under which this method would not be reliable.

Learn more about the method and Lincoln Index HERE.