Great question about dams! While dams change the ecological makeup of any river that they are placed in, their biggest impact for fish comes in relation to movement. Unless a dam is specifically built to allow fish to move both downstream and upstream, it becomes a barrier. To some fish this is more critical than others. Fish that are born in fresh water and later migrate to the ocean and eventually return again are called ANADROMOUS. In Idaho, the native salmon and steelhead in most of the state are typical of such fish. Here in the Upper Snake Region, fish in our stretch of the Snake River have been separated for thousands of years from the ocean by a huge natural barrier. Shoshone Falls, outside of Twin Falls Idaho naturally separated the ocean going fish from our resident fish.
In Idaho Falls, our stretch of the Snake River used to flow free so that native cutthroat trout could access tributary creeks to spawn. Today, they are still able to access some of these creeks, but their movement is limited to downstream movement only. They may survive a trip over the falls to reach a spawning tributary, but they are then stuck in that portion of the river. As long as fish keep coming from upstream or hatchery fish are added, than this model still allows the river to function in a somewhat natural manner.
Some of the introduced species of fish, such as the Brown Trout, are what are called main stem spawners. This means that they are able to successfully able to lay eggs in the main part of the river and don’t need to worry about going over the dams.
While the local dams have changed the makeup of the river, conditions are still good enough that another fish native to Idaho, but never able to access our waters naturally, was introduced by Idaho Fish & Game last year. About 75 White Sturgeon were released into the stretch of the Snake River that runs through town. These fish can live for over a hundred years and grow to incredible lengths. In order to let these fish continue to grow, they are catch and release wherever they are found in Idaho!
All fish have a balloon-like organ inside them known as a swim bladder. The bladder contains gas, which gives the fish extra buoyancy. The amount of gas can be increased or decreased whenever the fish needs to change its depth.
How does a swim bladder work?
Materials: Plastic soft drink bottle, sink or tub full of water
- The soft drink bottle will represent the swim bladder. Place the capped bottle in the water with only air in it. What happens?
- Now fill the bottle with 50% air and 50% water. What happens?
- Fill the bottle completely with water. What happens now?
Challenge: Add the correct amount of air and water to the bottle to make it sit 3 inches below the surface of the water.