Lesson Plan - Making a Redd

Material available and resources required

Download this lesson plan

IRP/Match grade

Science 3

Processes and skills of science

  • Ask questions that foster investigations and explorations relevant to the content
  • Measure objects and events

Support may be available

Contact your local Stream to Sea Education Coordinator or Community Advisor or phone 604-666-6614 to find out if an Education Coordinator in your area assists with this activity.

Lesson overview

In this hands-on classroom activity, students will build two model salmon redds (i.e. a nest made of gravel in which salmon spawners lay their eggs); one with and one without gravel. A simple experiment will demonstrate the different effects of flowing water and predators on exposed and sheltered salmon eggs. Students will compare experiment outcomes, discuss their experiments' conclusions, and consider how the experiment relates to a real stream.

Estimate of time required

Other required material:

Recommended additional resources and optional enrichment activities

(E.g. Web-sites, Teaching Guides, Student Reading, Videos/Audio-tapes, Posters and Brochures, Field Trips)

Activity description

This experiment demonstrates how a gravel redd protects salmon eggs from predators. If you have done "Unit Three: Salmon Eggs", you may prefer to replace parts one and two with a brief review.

General information

Materials

Time required: Three lessons

Level of conceptual difficulty: Moderate to advanced

Suggestions for assessment: Review students' discussion and observation pages to ensure that the students can describe how a redd protects salmon eggs from predators and strong water flows.

Introduction

Part 1

diagram:making a redd-experiment 1

Part 2

diagram: making a redd experiment 2

Part 3

With the class, compare the outcomes for the eggs in the open stream and for the eggs in the redd. Make a graph to compare the number of eggs that were washed away or caught by birds in parts one and two of the experiment.

Discussion

Discuss with the class what conclusions they can add to "Handout 9.2: Making a Redd Observation Page". If necessary, prompt them with questions, such as:

Were more eggs washed away with the redd or without?

Without.

Did the birds catch more eggs with the redd or without?

Without.

How was the redd in the basin like a redd in a stream? How was it different?

Similar materials and shape, but smaller, less water flow.

How would a redd help protect the eggs in a real stream?

It would hide the eggs from birds and keep them from washing away. It would also help protect the eggs from other predators, such as fish and raccoons, so more would survive.

Student handout

Prediction

Observation

Conclusion

Background information

Salmon Spawners - In the final stage of the salmon's life cycle, the adults re-enter their home river and swim back to the stream or lakeshore in which they grew as fry. Salmon from inland rivers may travel many hundreds or thousands of kilometres, swimming from 30 to 50 km a day against the current. They follow the scent of the water from their home stream, past rapids and other obstacles, such as dams, rock slides and log jams, before reaching their destination. Fishers and predators, such as bears, otters, raccoons and eagles, catch many salmon on their trip upstream.

When they enter fresh water, the salmon stop eating and live only on stored body fat. Their kidneys, gills and skin change to regulate the water and salt balance in their cells. To save energy, they lose the slime coating that helps protect them; their skin becomes thick and leathery, and they absorb their scales.

The salmon's appearance changes dramatically, with males and females developing distinct differences. Both males and females lose their silvery colour and take on deep red, green, purple, brown and grey colours. Their teeth become long and they develop a hooked jaw, which is particularly noticeable in the males. The body shape can change, with some species developing a pronounced hump on their back. Eggs ripen in the ovaries of the females, while sperm in the males changes into liquid milt.

When they reach their home stream or lake, the female uses her fins and tail to find a spot with the right gravel size and water conditions. With strong sweeps of her tail, she rearranges the stones in the gravel bed to form a redd, the nest-like depression in the stream- or lakebed where she will lay her eggs. Males fight among themselves to get close to a female. When a female chooses a male, they nudge and bump each other in an underwater courtship dance. The female deposits some of her eggs in the redd, and the male deposits his milt to fertilize them. Some species deposit up to 6,000 eggs, but the average is about 2,500. The female covers the eggs with gravel to protect them, and often moves on to build a second or third redd, which is fertilized by other males.

Both males and females die within a few days of spawning. Their bodies, battered and injured by the difficult trip upstream, decompose. Valuable nutrients from the carcasses form a rich food source for other fish and wildlife by fertilizing the stream or lake. Salmon carcasses that are carried onto riverbanks fertilize the forest and bushes. If most of the adult salmon are caught, the water will have few nutrients for the next generations of salmon and for the rest of the ecosystem.

Lesson Plan Written by Shelee Hamilton, edited by Elizabeth Leboe