In this lesson, students will investigate the life cycle of the salmon. Students will develop a model of the life cycle based on their observations from different sources, investigating the birth, growth, reproduction and death of an Alaskan salmon.
Two 45–minute class periods
Students will develop a model to identify and describe the life cycle of a salmon
• For the teacher – Computer with Internet access, projector
• Student Worksheet: Life Cycles (also linked in "For Student" support materials below)
- Do you know what a life cycle is? (You are trying to see if students are familiar with an organism living, changing as they grow, reproducing, and then dying. One part of the cycle flows into the other and the cycle repeats itself, over and over.)
- What are some plants or animals that have a unique lifecycle? (You are trying to get students to use their background knowledge, which may vary widely, although most students are familiar with the life cycle of a butterfly, frogs, and perhaps plants. Ask them to describe the way an animal or a seed changes in each part of the cycle.)
Capture responses in a visible format or ask students to write their responses.
Tell students: Now we are going to use your powers of observation to learn about the journey salmon make in order to lay their eggs and start a new cycle of life.
Play Video: Chris Kratt talks about how salmon survive
Play Video: Salmon Run: Wild Kratts
Discuss with Students: When salmon are adult's they swim back to the river or stream where they were born. You saw the adult salmon swim together, leaving the ocean to find their river or stream.
- What is it called when salmon group together and swim through the ocean back to the place where they were born? (It is called a salmon run.)
Ask students: Using information from the videos, what major life event do you think the salmon are preparing for? (Students may not be sure, as they are just learning about the life of salmon. But some may know these are adult salmon that will lay eggs – females – and fertilize eggs – males – once they find the place they were born. They are preparing to give birth to new salmon.)
Introduce to students the idea that salmon go through a life cycle: they are born, they grow and develop, they reproduce, and then they die. Have students compare this life cycle with a human’s life cycle – humans are born, they grow, they reproduce, and they die. The specific life cycle stages a salmon goes through are all very different from one another and unique from other animals. While most fish can live in only saltwater or freshwater, salmon actually change their bodies internally and survive in both environments. A salmon goes through up to seven stages in its lifetime, each distinctly different from the stage that precedes it. As the students watch the video clips and engage in conversation, they will learn about the stages in a salmon's life and recognize that each state is unique. Students will learn that these stages are a part of a life cycle.
The journey described in this first video is a difficult one. As salmon make their way back to the place they were born to lay their eggs, they face many obstacles.
Ask Students: What kind of obstacles do you think salmon have to negotiate as they swim upriver to lay their eggs? (Answers will vary.)
Tell Students: We will watch a video to see what some of these obstacles are.
Play Video: A New Obstacle: Wild Kratts
After watching, have students discuss the obstacles they noted in the video. In addition to their natural predators like bears and eagles, dams are obstacles to salmon. Dams with fish ladders are easier for salmon to pass. Students may also mention that fishing is another obstacle to salmon, although this is not shown in this clip.
Tell students: Now you will investigate each life cycle stage and learn more about the journey of the salmon. Watch the videos below carefully (using the student worksheet) to see how each stage differs from the others. After you watch and use the student worksheet, you will make a model.
Give students Student Worksheet: Life Cycles. Have them look at it before watching the video clips below. Students should use the worksheet to draw or note their observations describing each life cycle stage of the salmon. Note that salmon spend most of their life in the growth stage and students will learn about three specific growth stages in the videos.
Teacher Note: Each of the following videos show more than one stage of life. Read each Teacher Note below to identify the stage or stages emphasized in the video clip and for specific information about what the students should look for as they watch. After each video, ask students the questions below to prompt their use of the student worksheet.
Teacher Note: This video shows reproduction and the change adult salmon undergo as they move upriver to spawn. Have the students draw an adult spawning salmon in the box on the worksheet for reproduction. You may want to pause the video to have them observe the vibrant colors, humped backs, and hooked jaws of the male salmon.
Ask Students: How do the salmon’s bodies change as they get ready to reproduce? How do salmon lay egg? Where do salmon lay eggs?
Play Video: Laying Eggs: Wild Kratts
Teacher Note: The beginning of this video shows birth, during which a salmon builds a redd (or nest) and lays eggs. Have students draw what an egg looks like in the box on the worksheet for birth. The end of this video discusses death. See the last stage below.
Ask Students: What do salmon look like once they emerge from the egg?
Play Video: Alevin | The Next Generation: Wild Kratts
Teacher Note: This video shows the first growth stage called alevin. Have the students draw an alevin in the box on the worksheet for growth. Please note students will need to also draw a fry or smolt in this same box (see below).
Ask Students: See the little yolk sac attached to the newly hatched fish. How might this help the alevin?
Play Video: Salmon: Science Trek
Teacher Note: The beginning of this video clip shows a second growth stage, and the focus is on the fry or the smolt in the students’ worksheet. Have students choose either the fry or the smolt to draw in the same box on the worksheet for growth. A key characteristic of both are the stripes on their sides, which is quickly seen at 00:36. These help the fish hide amongst the gravel in a river – they are camouflage. After about 01:15, the video clip describes the salmon’s journey upstream and reproduction.
Ask Students: How are the fry or smolt different from the alevin?
Play Video: Laying Eggs: Wild Kratts
Teacher Note: Despite the title, the end of this video discusses death and what happens to the salmon once they have laid and fertilized the eggs. This stage may be upsetting to some students. It is important for them to know that the salmon’s death is very beneficial – its body decays and nourishes the ecosystem, so new life can grow. The decaying body helps the organisms that break things down (decomposers), giving food to small insects, plankton, and the plants growing in and around the water. This is an extremely important aspect of Alaska’s marine ecosystem.
You can ask the students how they would like to represent death in the diagram – perhaps an adult salmon upside down or a salmon with a circle/line over it? As an alternative, students may write a description of a salmon’s death – when it happens and the benefits it brings. Whatever the students decide, he/she should write or draw this stage in the box on the worksheet for death.
Ask Students: How do the salmon bodies, after their death, help the ecosystem?
Discuss with students: To wrap up Part 1, remind student that they have now learned about salmon in their life cycle stages. Salmon’s life cycle stages, which they should have noted on the student worksheet are:
1.) Birth – eggs
2.) Growth – alevin, fry, parr (not seen in the videos), and smolt
3.) Reproduction – spawning adult
Consider having students share with a partner or small group what they wrote or drew in Student Worksheet: Life Cycles. Consider projecting a worksheet on the whiteboard for all to see and, if needed, to help them with information they may have missed.
Tell Students: You are going to make a model that shows the different stages a salmon goes through in their lifetime. A model is a helpful tool that scientists use to describe ideas and explanations. Your model will help you represent each life cycle stage and how each one is different from the others.
Teacher Note: You may want to refer to page 1 of the resource Life Stages of Alaskan Salmon | Parent Activity Guide: Grades 3-5 to see one possibility of how to model the stages. Do not show this to students at this time. You will notice that the model in the Parent Activity Guide has both adult and spawning adult salmon, and a stage called a parr (a stage between a fry and a smolt). Your students’ models will look different than this example.
Tell Students: Cut out the squares of the drawings of the stages of salmon you drew in the Student Worksheet: Life Cycles.
• Give each student a piece of poster paper after they have cut out their drawings. Have the students help each other place their stages in a circle on the poster paper, in the order that makes sense to them based on what they have been observing. Students can start with any stage and then determine what the next stage would be. They need to be reassured that their cycle may ‘start’ differently than someone else’s, but when completed all cycles will show a similar sequence.
• Have students draw arrows, showing how one stage leads into the next. Then have the students glue or tape their squares onto the poster paper.
Tell students: By moving their drawings from a linear form in the student worksheet to a circle on the poster, students are representing the continuous cycle of life. Their circular model shows that after death, new life is formed and indicates that death is important in enabling new life.
• Have the students give a title to their model of the salmon’s life cycle, writing it either across the top or in the middle of the circle.
• Display the models of the salmon’s life cycle in a location where all students can walk around and view them.
Show page 1 of the resource Life Stages of Alaskan Salmon | Parent Activity Guide: Grades 3-5 after students have completed making their own model of the salmon’s life cycle. Have students look at the stages and compare them to their own models.
Ask students what differences they observe. They will most likely notice there are both adult and spawning adult and a stage called parr on the model in the Parent Activity Guide. Based on where the parr is shown on the life cycle model, they should be able to deduce that it is a stage between the fry and the smolt.
As students look at this handout, have them help you place the terms reproduction, birth, growth and death next to specific stages. For example, write ‘reproduction’ next to the adult salmon and/or the adult spawning salmon, ‘birth’ next to the eggs, etc. Students might wonder where to write ‘death’. This would also go next to the adult salmon or adult spawning salmon, as the salmon die after they reproduce.
Ask the students if they would modify their own model in any way, and if so, how and why. The emphasis here is a proper understanding of where birth, reproduction, growth and death occur during the life cycle of a salmon.
Have the students practice with each other how they would describe their model to another person and then consider having the students share their posters with other classes or grade levels, parents and/or the public. Students should be able to give basic information about each stage.
Give the students the second page of the Life Stages of Alaskan Salmon | Parent Activity Guide: Grades 3-5 to color. Do not give them this until they are finished with their own model.
To assess student understanding of the salmon life cycle, evaluate their responses on Student Worksheet #1: Life Cycles - Salmon Information as they fill them out and before they cut them apart for their models.
Check their poster models to see that the stages are placed in an order that reflects the correct stages of a salmon’s life.