The Salmon Spawner

Materials: 

• Two 25-metre lengths of rope 

• Four pylons or cones 

• Four to six floor mats, tied into rolls 

• One copy of “Handout: The Salmon Spawner” for each student 

• Writing supplies or art supplies 

Time required: Approximately 

30 minutes in the gym and 30 minutes in class 

Preparation 

• In a gym or open area, place two ropes on the floor, parallel to each other and about four metres apart. Mark the ends of each rope with pylons or cones. Explain that the ropes represent the banks of a straight-sided stream. 

• Have the students find a place in the gym where they can sit without being close enough to touch anyone else. Ask them to find a comfortable position and close their eyes as you read “Handout: The Salmon Spawner” to them. This should help them to relax and focus on the instructions, while minimizing any potential “rough play”. 

Simulation 

• Have about six students move slowly between the ropes, as if they were spawners swimming upstream. Have another six students link arms and move rapidly (but carefully) side-by-side between the ropes in the opposite direction to the spawners. Explain that they represent a wave of water moving downstream. Have the rest of the class observe how the rapidly moving water pushes the spawners along.• Lay some rolled-up mats across the ropes so they are partly in and partly out of the stream”. Explain that the mats represent logs, boulders and other obstructions in the stream. Have another group of spawners move upstream, while another wave moves downstream. Have the class observe how spawners can hide behind the logs to rest and to avoid the wave. • Explain that gravel can accumulate in slow-moving waters and change the shape of the stream bank. Move the ropes so that they curve around the logs and obstructions. Have another group of spawners move upstream, while another wave moves downstream. Have the rest of the class observe how the wave becomes slower as it moves around the curves, and how it can move the stream bank, itself.

Discussion 

Have students describe the difficulties in working along the stream under the different conditions. If necessary, prompt them with questions, such as: • In which stream did spawners have the most trouble? In which was it easiest to make it to the end? • What made one part harder than another? • In what ways is the stream similar to the streams a salmon must travel on its trip upstream? How is it different? A salmon also has to jump and slide past a variety of obstacles. It may be easier for a salmon to swim through a wave of water, but its trip is much longer, and the salmon has no hands or feet to help it. • What kinds of obstacles does a salmon have to pass on its migration upstream? Rapids and waterfalls, logs, dams, dried out sections of streams, fishing nets, polluted water, predators, etc. • What natural features help a salmon in its migration upstream? Salmon can find pools behind rocks and logs to rest, and slower water along the edges of a river. Also, their skin becomes very tough, they can jump very high, and use their strong muscles to push their way along.

Summation

Have students, in groups, review “Handout: The Salmon Spawner” and list at least five changes that salmon face in the last stage of their life. Have students, as individuals, draw or describe in writing

Handout: The Salmon Spawner

In the final stage of their life cycle, salmon re-enter their home river and swim back to the stream or lakeshore from which they emerged as fry. Some travel many hundreds or even thousands of kilometres, swimming from 30 to 50 km a day against the current. They follow the scent of the water to their home stream. Fishers and predators such as bears, otters, racoons and eagles catch many salmon on their trip upstream. When they enter fresh water, salmon usually stop eating and live only on stored body fat. To save energy, they lose the slimy coating that helps protect them, their skin becomes thick and leathery, and they start to absorb their scales. Some internal organs may fail on the journey. The salmon’s appearance changes dramatically, with males and females developing distinct differences. They 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 pronounced in males. Their body shape can change, with some species developing a distinct hump on their back. Eggs develop in the ovaries of females, while males develop sperm. When she reaches her home stream or lake, the female uses her fins and tail to find a spot with the right gravel size and water conditions. With 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. The female deposits her eggs in the redd, then the male deposits his sperm 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, often moving on to build a second or third redd which may be fertilized by other males. Both males and females die within a few days of spawning. (Steelhead and cutthroat may survive to spawn more than once, although once is most common. If they survive, they go back out to sea as kelts, spawned-out salmon, then return to the spawning area in another year or two. Altogether, they may spawn three or four times.) The salmons’ bodies decompose, releasing valuable nutrients, including minerals from the sea. The nutrients from the salmon carcasses form a rich food source for other wildlife, as well as fertilizing the stream and lake along the shore. When salmon carcasses are carried onto the riverbank, they also fertilize the forest and bushes. The ocean compounds in the salmons’ bodies can be very scarce in the upstream environment. If few adult salmon return to spawn, the lack of nutrients can make the forest and the water a poor environment, with few nutrients for growing salmon fry and other species.