Estimating Population Size

Fishing is a great way for people of all ages to relax and enjoy time together. This popular pastime is celebrated annually on National Go Fishing Day on June 18. Of course, if it gets too popular, there’s the danger that fish populations may dwindle. To keep people from overfishing, many local authorities have put measures in place to control the number and type of fish that can be caught.

One method scientists use to monitor fish populations is called “capture/recaputure.” In the Estimating Population Size Gizmo, students simulate this method to estimate population size. In the Gizmo, students catch and tag fish in a pond, return them, and then catch a second group of fish. Then they use the number of tagged fish caught to write a proportion and estimate the fish population of the pond.

For example, suppose students tag and release 20 fish. If they catch 10 fish and only 1 is tagged, then it is reasonable to guess that about one-tenth of the fish are tagged. So, they can estimate that the population is 20 times 10 or 200 fish.