A role-playing game where students get the opportunity to experience life as a salmon and some of their major challenges
Objectives: #
Students will (1) describe how some fish migrate as part of their life cycles, (2) identify the stages of the life cycle of a trout or salmon, (3) describe limiting factors that affect Atlantic salmon as they complete their life cycles, and (4) generalize that limiting factors affect all populations of animals.
Method: #
Students will simulate the Atlantic salmon and the hazards they face in an activity portraying the life cycle of these aquatic animals.
Materials: #
- Large playing area (100 feet x 50 feet)
- 500 feet of rope or string or 6 traffic cones for marking boundaries (masking tape may be used indoors)
- Two cardboard boxes
- 100 tokens (index cards, poker chips, macaroni, etc.)
- Jump rope
- Hooks and Ladders diagram
Background: #
Many fish migrate from one habitat to another during their lives. Both the Atlantic salmon and the Pacific salmon are examples of fish that migrate.
The life cycle for the Atlantic salmon begins when the female deposits her eggs in a redd, or nest. The female will clear away gravel with a flip of her powerful tail, forming a nest where the eggs will be deposited. Once she deposits the eggs, the male will fertilize them. Both the male and the female fish will gently push the gravel back over the nest, helping to protect the eggs from predators. Eggs may also be susceptible to oxygen deprivation at this time.
Newly hatched salmon, called alevins, will stay in the gravel, feeding on the yolk-sac from their egg. Once all the nutrients from the yolk-sac have been used, the young fish, fry, begin feeding and move into deeper water. Atlantic salmon will spend their first few years in small streams and rivers, where they feed on aquatic insects and other small matter. These fish are relatively solitary, and will defend their feeding territory. At this life stage, these young fish are called parr.
After reaching approximately 4 inches, the smolt stage, these fish are ready to begin their springtime journey downstream towards the ocean. These fish will feed in estuaries where fresh and salt water meet as their body adjusts to a life in the brine. After a few weeks, the fish are ready to enter the ocean.
In the ocean, the salmon grow quickly, feeding on other fish, shrimp and crustaceans. They feed as they are migrating to their major feeding grounds in the North Atlantic near Iceland and Greenland. These young salmon may encounter limiting factors, such as seals, larger fish and humans.
Atlantic salmon will spend 1-2 years in the ocean before beginning their trek home. It is believed that salmon use a magnetic or sun compass to find their way to the coast of their natal stream and from there use olfactory clues to find the river and tributary of their birth. These salmon, unlike the Pacific salmon, may spawn another one or two times before dying.
Salmon face a number of limiting factors during the course of their lives. A limiting factor is a reason or cause that reduces the population of an organism. Some limiting factors are natural and some result from human intervention into natural systems.
Natural limiting factors include drought, flood, predators and inadequate food supply. Throughout their lives salmon rely on a habitat that provides shady streams and deep pools for spawning and resting. Logging, grazing, mining, road building and development may destroy streamside vegetation, erode land and fill streams with sediment.
Dams are another limiting factor that block or slow migration to and from the ocean. Salmon become disoriented by the reservoirs formed by dams and are exposed to high water temperatures and predators. Fish ladders can be installed to help salmon through the dams. Fish ladders can be water-filled staircases that allow migrating fish to swim around the dam.
Another threat to salmon is overfishing. That, along with habitat destruction, is part of the cause for the decline in salmon populations.
NOTE: All possible conditions are not covered by the design of the activity. However, it does serve to illustrate three important concepts: life cycle, migration and limiting factors.
Procedure: #
1. Ask students what they know about the life cycles of fish that live in their area. Do any local fish migrate to spawn? If yes, which ones (shad, lake trout, striped bass, suckers, carp and salmon are examples).
2. Set up a playing field as shown in Diagram 1, including spawning grounds, reservoir, downstream, upstream and the ocean. The area must be at least 100 feet by 50 feet. Assign roles to each of the students. Some will be salmon; some will be potential limiting factors to the salmon. Assign the student roles as follows:
• Choose two students to be the turbine team. They will 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, those students move to the upstream side to become the waterfall-broad jump monitors (see diagram)
• Choose two students to be predatory wildlife. At the start of the simulation, the predators will be stationed in the reservoir above the turbines to catch the salmon fry as they move downstream. Then they will move below the turbines where they catch salmon heading downstream. Later in the activity, when all the salmon are in the sea, these same two predators will patrol the area above the “broad jump” waterfalls. There they will feed on salmon just before they enter the spawning ground (see diagram).
• Choose two students to be humans in fishing boats catching salmon in the open sea. The students in the fishing boats must keep one foot in a cardboard box to reduce their speed and maneuverability.
• All the remaining students are salmon.
NOTE: These figures are based on a class of 20-30, adjust the number of limiting factors accordingly.
3. Begin with all the salmon in the spawning ground. The salmon first move into the reservoir above the dam. They must stay in the reservoir until they count to 30. This pause simulates the disorientation that salmon face because of a lack of current in the lake to direct them on their journey. During this time the predators may catch the salmon and escort them one at a time, to become part of the fish ladder. The salmon then start their journey downstream. The first major limiting factor that the salmon encounter is the 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 jump-rope swingers’ arms if they do not get touched while doing so. A salmon dies if the turbine (jump-rope) hits it. The turbine operators may change the speed at which they swing the jump rope. Any salmon that “dies” at any time in this activity must immediately become part of the fish ladder. The student is no longer a fish, but becomes part of the physical structure of the human-made fish ladders now used by migrating salmon to get past barriers such as dams. The students who are the fish ladders kneel on the ground as shown in the diagram with one body space between them.
4. Once past the turbines, the salmon must pass some predatory wildlife. The predators, who have moved from the reservoir area to the area below the turbine, 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. Later, the salmon that survive life in the open ocean will pass through the fish ladder to return to the spawning ground. NOTE: Both the predatory wildlife in the downstream area and the people fishing in the open ocean must take the dead salmon to the fish ladder site. This action moves predators and fishing boats off the field regularly, helping to provide a more realistic survival ratio.
5. Once in the open ocean, the salmon can be caught by fishing boats. The salmon must move back and forth across the ocean area in order to gather four tokens. Each token represents ½ year of growth (2 years), that fish can begin migration upstream. The year tokens can be picked up only one at a time on each crossing. Remember that the salmon must cross the entire open ocean area to get a token. The “two years” that these trips take, make the salmon more vulnerable; thus they are more readily caught by the fishing boats. For 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.
6. When four tokens are collected, the salmon can start upstream. The salmon must walk through the entire pattern of the fish ladder. This enforced trip through the fish ladder 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.
7. Once through the ladder, the salmon face the broad-jump waterfall. The waterfall represents one of the natural barriers salmon face going upstream. Be sure the jumping distance is challenging but realistic. 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 can be changed to a stepping-stone jump defined by masking tape squares on hard floors.
8. Above the falls, the two predators who started the simulation, as the predators below the turbines have now become the last set of limiting factors faced by the salmon. They represent bears, one example of predatory wildlife. Again, remember that the predators must catch salmon with both hands. If they catch a salmon, they must then take the student they caught to become part of the structure of the fish ladder.
9. Since Atlantic salmon can spawn more than once, have the salmon complete as many full migratory trips as possible, then at the end of the activity, report how many times they completed the migration. Graph the data. Have the students explain how age influence mortality rates and susceptibility to limiting factors.
10. The activity is done when all the salmon are gone before the spawning ground is reached – or when all surviving salmon reach the spawning ground.
11. Next engage the students in a discussion. Explore such topics as
• The apparent survival or mortality ratio of the salmon,
• The role of barriers
• The role of predatory wildlife and the people fishing,
• Where the losses were the greatest
• Where the losses were the least,
• What the consequences would be if all the eggs deposited made the journey successfully, and
• What seemed realistic about this simulation and what did not?
12. 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. Make sure the students have a clear working definition of limiting factors. Encourage students to make the generalization that all animals – not just Atlantic salmon – are affected by limiting factors. Ask the students to give examples of limiting factors. They might mention the availability of suitable food, water, shelter and space, disease, weather, predation and changes in land use and other human activities.
Activity Extensions: #
- Write a report on the life cycle of the Atlantic salmon. Create a mural showing the life cycle of the salmon.
- Research and illustrate the life cycle of any local fish. If possible, look for one that migrates.
- Compare how the life cycle of an Atlantic salmon is similar to and different from the life cycle of one or more local fish.
- Investigate similarities and differences in the migration and life cycles of the Atlantic and Pacific salmon. Investigate the life cycle of the salmon in the Great Lakes region of the United States.
- 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.
- Consider this approach, and try the activity again: In the past 100 years, salmon have experienced many new, human-caused limiting factors. Dams, commercial fishing, timber harvest, and road construction have had a tremendous impact on salmon populations. In 1991, the Snake River sockeye salmon was placed on the federal endangered species list. In the past, tens of thousands of sockeyes would make the 900-mile return trip from the sea to Idaho’s mountain streams and lakes. There they spawned and died. Their offspring hatched and began their early development in fresh water. The actual migration to the Pacific Ocean could be completed in as few as 9 days. Today that trip takes more than 60 days. In 1991, only four Snake River sockeye returned to their spawning grounds
To simulate these increases in salmon limiting factors, play several rounds of the Salmon Survival Game. Allow each round to represent the passage of 25 years. Start in 1850. In that year, do not include dams or commercial fishing operations in the scenario. As time passes, add the human commercial fishing operations. Build dams (jump ropes) as the scenario progresses into the 21st century.
Describe some of the possible effects on salmon from increased limiting factors as a result of human activities and interventions. Discuss possible positive and negative effects on both people and salmon from these increases in limiting factors affecting salmon. When the activity reaches the “present,” predict what might happen to salmon in the future. Recognizing the complexity of the dilemma, discuss possible actions, if any, that might be taken to benefit both people and salmon.
10. Find out if salmon exist in your state. If so, are they native or were they introduced?
Evaluation: #
1. List, describe and illustrate the major stages in an Atlantic salmon’s life cycle.
2. Identify and describe some limiting factors that affect salmon as they complete their life cycles.
3. Identify and describe some limiting factors that might affect other animal populations.
