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  Teaching Guide

Activity 1: Grades 5-8
Salmon Homing

Although the ability of salmon to return to a home stream may depend on a variety of cues, most researchers believe that scents within the water are the primary cues the fish rely on for homing to a specific stream. Scientists believe the specific odor cues of a stream might be embedded within the genetic makeup of each fish. Factoring in this possible genetic influence is critical when raising new stocks.

Image of salmon

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This activity page will offer:

  • An opportunity to detect and differentiate odors
  • An opportunity to apply odor discrimination to uncovering a trail
  • A cooperative challenge in which students work together to uncover a series of trails


Finding Your Way
In this activity, students will be challenged to record a path based upon olfactory cues. Scents placed at critical junctures will set the fixed path that each team must follow.


  • Paper cups
  • Paper towels
  • Pencil
  • Yard stick
  • Five different and distinct scents
  • Yarn
  • Tape

    NOTE: To best perform this activity, the class should be divided into two groups. One group creates the scent trails. The other group uncovers them.

Before You Begin
The activity is performed on a grid that has been laid out on a large flat surface area (such as a gymnasium floor.) To build the grid, you'll need to use a yard stick and tape. Each line of the grid is separated by one yard. In addition, the distance between neighboring grid points (marked by a taped "X") is also one yard. Using the same distances, identify both the staring point and the home stream. Here's what the completed grid looks like:


Steps (For the set-up)

  1. Work in teams of two. Obtain a homing scent from your instructor.
  2. Obtain seven paper cups. Use a pencil or other sharp object to carefully punch several holes into the cup.
  3. Crumble a piece of paper toweling and stuff it into the cup.
  4. Add several drops of your scent to the paper toweling.
  5. Invert the cup and place one cup at any of the grid "X"s.
  6. You'll need to agree with other teams on cup placement.Place a second cup on the next line. Try to mix up the positions so a zigzag pattern emerges.
  7. Keep placing your scented cups until one has been positioned on each of the five lines.
  8. Don't forget to place one cup at the starting line and another at the "home" target.
  9. Make a record of this pattern.

    Here's what the punched cup over the mark looks like:


Steps (For uncovering trails)

  1. Work in groups of two. Randomly select one of the five scents.
  2. Begin at the starting point. You should have a long length of yarn and a roll of adhesive tape.
  3. When the instructor gives the signal, find the cup in the first line that contains your assigned scent.

    (NOTE: Your instructor will demonstrate the proper sniffing technique.)
  4. Tape one end of the yarn to spot where your starting cup is positioned.
  5. Move on to the next row. Locate your scent cup. Continue to lay down a yarn trail and tape it to the appropriate spot.
  6. Continue uncovering and recording your scent trail until you reach the finish.
  7. Make sure that all of the scent trails have been completed and all the cups used in determining the separate and distinct trails. Here's an example of what the finished the finished scent trails might look like.


  1. Why was it necessary to punch holes in the scent cups?
    (You needed holes through which the odor could escape.)
  2. What was the purpose of the yarn?
    (It was used to record the travel from the start to the finish.)
  3. What was the purpose of the cups?
    (They were odor landmarks on which the course was based.)

Communicating by Dance
Could you demonstrate the homing of salmon by choreographing and performing a dance? In addition to the fish, make sure to include scents and several branching streams that support different salmon populations.

Genetic Window?
Is the ability to detect certain odors in humans genetic? Is your immediate family more sensitive to certain odors than members of another family? With your instructor's approval, design a strategy for inquiry that would explore this relationship. Create a controlled experiment that might show if there is a genetic component to sensitivity to different odors.

Diluting Odors
How does diluting odors affect a person's ability to detect them? Think about it. Then, with your instructor's approval, design an experiment that would test how a dilution of different scents affects their ability to be detected. Use a variety of odors. Which ones can be diluted most and still be detected? Which odors become undetectable with even the slightest dilution?

Web Connection

Investigations into how salmon find their home stream
This site offers an overview of salmon homing and some of the classic behavior experiments.

Salmon Genetics at Heart of Endangered Species Listing Debate

This site presents a rich overview of salmon genetics studies.

Academic Advisors for this Guide:
Corrine Lowen, Science Department, Wayland Public Schools, Wayland, MA
Suzanne Panico, Science Teacher Mentor, Cambridge Public Schools, Cambridge, MA
Anne E. Jones, Science Department, Wayland Middle School, Wayland, MA
Gary Pinkall, Middle School Science Teacher, Great Bend Public Schools, Great Bend, KS



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