Population Estimates and Determining Population Numbers


Many Fisheries and Wildlife biologists and managers have many duties and tasks that they must perform on a daily basis within their jobs. One of these tasks is to estimate the populations of various wildlife and to try to project these populations for years to come. 


Estimating populations of wildlife can be a very difficult and meticulous task, but when done correctly it will provide crucial information to wildlife agencies everywhere. Agencies then can use this data to set hunting season dates, track animal movement, regulate recreational activities, and simply manage our resources. 

Agencies must understand and take into account a few factors before they can begin to estimate populations. These include knowing the historical numbers of animals in a given area, know what the predator prey ratio is close to, understand the dynamics and behavior of the population, immigration and immigration rates and other biological factors.


There are a couple different ways that managers can estimate populations. They can either use a change in ratio method, or a mark and recapture method.  

The change in ratio method is a good way to estimate the size of a population. Attached is a link with some background information on this method. https://link.springer.com/chapter/10.1007/978-94-011-2868-1_9  This method also contains an equation. The equation is as follows: N= (C-(p2)(C))/(p2-p1). Where C is number that is added or subtracted, p1 is the proportion that was first observed and p2 was the second proportion that was observed. 

The Mark and Recapture method is the other way of estimating a population by capturing and marking the animals and then recapturing another set of animals and seeing how many have already been marked then estimating the population from that. There is another equation that is associated with this method. Like most equations, it is a matter of plugging in the variables and solving the rest. Attached is a link to the equation and a lab is embedded within this link. http://www.cee.org/tep-lab-bench/pdf/PopulationSize.Worksheet.pdf