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Salmon for Teachers

fish rescueHooks and Ladders

This lesson plan can be adapted for students in grades 3-9. Students simulate Pacific salmon and the hazards faced during their seaward and return migrations.

 

Background

In this two-part activity, students will learn about the seaward and spawning migrations of the Pacific salmon, and the hazards of these journeys.

Within their genetic fiber, Pacific salmon have an encoded instinct that drives them to migrate from their freshwater spawning beds downstream into the sea. Once in the sea they spend several years reaching the maturity needed for their single return journey to their original hatching ground. There the salmon spawn and die. Salmon face a variety of hazards that serve as limiting factors in the completion of their life cycle. Limiting factors are factors that reduce the populations of living organisms. Sometimes the limiting factors are natural and sometimes they result from human intervention with natural systems.

The small ocean-bound salmon, called "smolts," are at once confronted by hazards on their downstream journey. Dams slow salmon migration. Because salmon cannot find the current behind dams, they become disoriented in reservoirs. When disoriented, salmon are extremely vulnerable to predators. Low water in streams, predatory birds, mammals, and larger fish pose additional hazards. Up to ninety percent of the salmon that hatch never reach the sea. When in the ocean, the salmon grow rapidly by feeding on the ocean's rich food supply. Predators such as sharks, killer whales and other marine mammals take their toll. In addition, humans catch salmon commercially and for personal reasons, including food and recreation.

In two to five years, the Pacific salmon start the journey that will guide them back to the rivers and streams leading to their own hatching site. The upstream migration from the ocean is also a series of hazards. For example, dams hinder their journey and would block it completely if fish ladders were not installed. Humans who fish, eagles, bears, and other predatory mammals also reduce the numbers along the way to the spawning ground. Sometimes landslides and logjams provide unexpected new barriers. So too do the natural waterfalls and rapids that the now weighty salmon must overcome. Once back at the spawning ground the life cycle of the Pacific salmon begins anew.

At the beginning of the twentieth century, salmon faced limiting factors such as predators in the ocean and river, and commercial fishing. Since that time, salmon have experienced many new, human-caused limiting factors. Dams, commercial fishing, timber harvest and road construction have had tremendous impact on salmon populations. In the past, smolts could migrate from Idaho's mountain streams and lakes to the Pacific Ocean in as few as nine days. Today that trip takes more than 60 days. Tens of thousands of Sockeyes used to make the 900-mile return trip from the sea to their home streams and lakes. In 1991, only four Snake River Sockeye salmon returned to their spawning grounds.

To simulate the effects of these increases in salmon limiting factors, students play two rounds of "Hooks and Ladders." The first round simulates spawning migrations prior to the twentieth century; the second round simulates the current migration obstacles of dams, turbines, fish ladders, reservoirs and increased predation.

 

Materials

  • large playing area (100 feet x 50 feet)
  • about 500 feet of rope, string, or six traffic cones for marking boundaries (masking tape may be used if area is indoors)
  • two cardboard boxes
  • 100 tokens (3 x 5 cards, poker chips, etc.)
  • jump rope

 

Objectives

The student will be able to:

  1. Recognize that some fish migrate as part of their life cycle.
  2. Describe limiting factors affecting Pacific salmon as they complete their life cycle.
  3. List, describe, and illustrate the major stages in a Pacific salmon's life cycle.

 

Instructions for Round One of Hooks and Ladders

barge fishery

  1. Set up a playing field (100 feet by 60 feet) as shown in the illustration, including spawning grounds, downstream, upstream, and ocean. Assign the following roles:

    • two students: predatory wildlife. At the start of the simulation, the predators will be stationed downstream. Later in the activity, these same two predators will patrol the area above the broad jump waterfall. There they will feed on salmon just before they enter the spawning ground.

    • two students: humans in fishing boats catching salmon in the open ocean. These students must keep one foot in a cardboard box to reduce their speed and maneuverability.

    • two students: broad jump waterfall monitors.

    • All remaining students are salmon.

    NOTE: These figures are based on a class size of 25 to 30. If the group is larger or smaller, adjust the number of fishing people and wild predators accordingly.

  2. Begin the activity with all the salmon in the spawning ground. Explain that they are "smolts"--small, silvery salmon that can be caught by predators in the rivers. The salmon then start their journey downstream.

  3. During this time, the predators may catch the salmon and escort them one at a time to the sidelines. The predators must catch the salmon with both hands--tagging isn't enough.

  4. Once in the open ocean, the salmon must move back and forth to gather four tokens. Each token represents one year of growth; the salmon can pick up only one at a time on each crossing, and then must cross again to pick up the next.

    The "four years" these trips take make the salmon more vulnerable and thus they are more readily caught by the fishing boats. For purposes of this simulation, the impact of this limiting factor creates a more realistic survival ratio on the population before the salmon begin the return migration upstream.

  5. When a salmon has collected four of the year tokens, it can begin migrating upstream. Although adult salmon do face some predators in their upstream migration, in this simulation they will not encounter any until they are close to their spawning grounds.

  6. Just before the spawning grounds, the salmon faces the broad jump waterfall. The waterfall represents one of the natural barriers the salmon must face going upstream. Be sure the jumping distance is challenging but realistic. Two students will monitor the jump. The salmon must jump the entire breadth of the waterfall to be able to continue. If the salmon fails to make the jump, then it must try again.

    NOTE: When playing indoors, the broad jump waterfall may be changed into a stepping stone jump defined by masking tape squares for safety on hard floors.

  7. Above the falls, two predators represent the last set of limiting factors faced by the salmon: bears, which typically prey on salmon on their spawning grounds. Again, remember that the predators must catch the salmon with both hands. If they do catch a salmon, they must then take the students they caught to the sidelines.

  8. The activity ends when all the salmon are gone before the spawning ground is reached--or when all surviving salmon reach the spawning ground.

 

Round Two of Hooks and Ladders

salmon

  1. Set up a playing field as before, adding the reservoir. Assign these roles:

    • Two students to be the turbine team. They operate the jump rope, which represents the turbines in hydroelectric dams. Later in the simulation, when all the salmon have passed the turbine going downstream, these students become the broad jump waterfall monitors.

    • Two students to be northern pike minnow. They are stationed in the reservoir above the turbines to catch the salmon smolts as they try to find their way out of the reservoir.

    • Two students to be predatory wildlife. They are stationed below the reservoir. Later in the round, these same two predators will patrol the area above the broad jump waterfall. There they will feed on salmon entering the spawning ground.

    • Two students to be humans in fishing boats catching salmon in the open ocean. These students in the fishing boats must keep one foot in a cardboard box to reduce their speed and maneuverability.

    • All remaining students are salmon.

    NOTE: These figures are based on a class size of 25 to 30. If the group is larger or smaller, adjust the number of people who are fishing and predatory wild animals accordingly.

  2. Begin the activity with all the salmon in the spawning ground. The salmon first move into the reservoir above the dam. They must stay in the reservoir for twenty seconds. This simulates the disorientation that salmon face due to a lack of current in the lake to direct them on their journey. During this time, the predators-- which simulate northern pike minnow, a native predator that thrives in the warm, still water of a reservoir--catch the salmon by tagging them with only one hand. The "eaten" salmon put themselves into the fish ladder. Salmon that avoid predators can continue their journey downstream. Next, they encounter a major hazard: turbines at the dam. At most dams, escape weirs guide migrating salmon past the turbines. The student salmon cannot go around the jump rope swingers, but they can slip under the swingers' arms if they do not get touched while doing so. A salmon dies if it is hit by the turbine (jump rope). The turbine operators may change the speed at which they swing the jump rope.

    NOTE: Any salmon that "dies" at any time in this round must immediately become part of the fish ladder. The students who are the fish ladder kneel on the ground, a body-wide space between them.

  3. Once past the turbines, the salmon must get past some predatory wildlife. These predators must catch the salmon with both hands--tagging isn't enough. Dead salmon are escorted by the predator to become part of the fish ladder.

    NOTE:Both the predatory wildlife in Step 3 and the people fishing in the open ocean must take dead salmon to the fish ladder site. This gets the predators and fishing boats off the field regularly, helping to provide a more realistic survival ratio.

  4. Once in the open ocean, the salmon can be caught by fishing boats. As in round one, the salmon must move back and forth across the ocean area in order to gather four tokens.

  5. bear catching salmonWhen a salmon has collected four tokens, it can begin migrating upstream. The salmon must walk through the entire pattern of the fish ladder. (See illustration below.) This gives the students a hint of how restricting and tedious the upstream journey can be. In the fish ladder, predators may not harm the salmon.

  6. Once through the ladder, the salmon faces the broad jump waterfall as in round one. The two former turbine students will monitor the jump. The salmon must jump the entire breadth of the waterfall to be able to continue. If the salmon fails to make the jump, then it must return to the bottom of the fish ladder and come through again.

    NOTE:When playing indoors, the broad jump waterfall may be changed into a stepping stone jump defined by masking tape squares for safety on hard floors.

  7. Above the falls, the salmon again face two predators, both bears, which typically prey on salmon on their spawning grounds. (These predators have moved from the downstream predation site of Step number 3.) Again, remember that the predators must catch the salmon with both hands. If they do catch a salmon, they must then take the students they caught to become part of the structure of the fish ladder.

  8. The activity ends when all the salmon are gone before the spawning ground is reached--or when all surviving salmon reach the spawning ground.

  9. After completing both rounds, discuss the activity. Explore topics such as:

    • the apparent survival-mortality ratio of salmon

    • the students' feelings throughout the activity

    • the role of the barriers

    • the role of the predatory wildlife and the people fishing

    • where the losses were greatest

    • where the losses were least

    • what the consequences would be if all the eggs deposited made the journey successfully

    • what seemed realistic about this simulation and what did not

  10. Ask the students to summarize what they have learned about the life cycle of salmon, the salmon's migration, and limiting factors that affect salmon.

 

Variation: Steelhead

This activity can easily be adapted to feature steelhead. Steelhead make their complete migratory journey and spawn two or more times; salmon die after spawning only once. To adapt this activity for steelhead, students are to make as many complete migratory trips as possible. After the activity is finished, ask students to report how many times they successfully completed the migratory cycle. Graph the data. Have the students explain how age influences mortality rates and susceptibility to limiting factors. Do they think many steelhead still make more than one roundtrip?

 

Extensions

  • Write a report on the life history of one of the species of salmon (e.g., Chinook, chum, pink, coho, Sockeye). Create a mural showing the life cycle of this salmon.

  • Compare the life cycle of a Pacific salmon to the life cycle of one or more other kinds of local fish.

  • Investigate similarities and differences in the migration and life cycles of Atlantic and Pacific salmon. Investigate the life cycle of salmon in the Great Lakes ecosystem.

  • Visit fish hatcheries that work with migratory species and investigate how they function.

  • Explore ways that dams can be modified to let fish safely pass downstream and upstream. Design the "perfect" fish ladder.

  • Investigate and discuss commercial fishing for salmon. Investigate and discuss personal, including recreational, fishing for salmon.

  • Find out about laws protecting migratory species, including fish.

  • Substitute striped bass for salmon. The striped bass is more widely distributed along the United States' coastlines than either the Atlantic or Pacific Salmon. Like the salmon, striped bass reproduce in freshwater and migrate to and mature in saltwater. They also must face the limiting factors outlined in this activity.

Back to Fish and Game Activities

Idaho Dept. of Fish and Game

Thanks to Idaho Fish and Game and Project WILD for all of their help and information.

All information in these sites from "Wild About Salmon" is copyrighted by the Idaho Department of Fish and Game and Idaho Project WILD, 1999.

Written permission was granted to use this material for educational purposes.

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