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The secret of fish swimming upstream: Why do only 3% of American sharks make it home?
It is a natural phenomenon for fish to swim upstream to reproduce, but the journey is not easy. According to some studies, only 3% of sharks in the United States successfully cross various man-made barriers and return to their spawning grounds. Such data makes one wonder: What factors make these fish face such difficult challenges in their long-distance journey?
"The speed of the water, the design of the obstacle, and the swimming ability of the fish themselves will affect their ability to pass smoothly."
With the progress of the industrial age, the construction of dams and various water conservancy facilities has sprung up like mushrooms after a rain. These facilities have had a considerable impact on the natural migration of fish. Especially for those fish that rely on long-distance fishing for their livelihood, a successful return home depends not only on their swimming ability, but is also closely related to the design of water conservancy facilities.
History of the development of fishways
The origin of fishways can be traced back to 17th century France, when people began to use branches and other natural materials to build simple fishways to help fish cross water obstacles. Since then, as technology has evolved, various forms of fish passes have emerged, including pool and dam structures, blocked fish passes, fish elevators, and new types of fish locks.
“The effectiveness of a fishway often depends on its design, which will hopefully reduce fatigue and hindrance to the fish.”
Causes of fish fatigue
Even if a fishway is designed, if the water flow is too fast, fish cannot pass through effectively and may even be washed back downstream. This has forced experts to rethink the design of fishways and take more into account the swimming abilities of different fish species. For example, the American shark's upstream swimming requires a lot of water speed and energy consumption, which is a problem that often causes it to struggle in the waterway.
Types of fishways
There are many designs of fishways, including:
- Pool and Dam Fishway
- Blocking the fishway
- Fish Elevator
- Rock Ramp Fish Pass
- Vertical slot fish channel
- Fish Cannon
Pool and dam fishway
This is one of the oldest fishways, usually consisting of a series of small dams and ponds that provide a convenient passage for fish to swim upstream. The fish need to jump between the boxes in order to make their way upstream.
Blocking the fishway
This design uses a series of enclosed baffles to redirect water flow, helping fish navigate around obstacles.
Fish Elevator
Fish elevators provide a way to transport fish directly over obstacles, especially tall obstacles.
Rock Ramp Fish Pass
This fishway simulates a natural water flow structure, using large rocks and wood to create small waterfalls, providing a good breeding habitat for fish.
Vertical slot fish channel
This design allows fish to pass through narrow slots without having to jump, which helps eliminate fish fatigue.
Fish Cannon
This system uses air pressure to gently launch fish into target waters, inspired by technology originally used to safely transport apples.
Validity Issues
Although the number of fish passes has increased, their effectiveness has been mixed. One study found that only 3% of sharks in the United States successfully pass through all fish passages and return to their breeding grounds. This has led scientists to think about how to improve the design of fishways and increase the success rate of fish return.
“Matching swimming performance data with hydrodynamic measurements is essential for planning effective fish passes.”
When designing fish passes, ecologists and engineers face several challenges, including linking swimming performance data with measurements of hydrodynamics. Fish's swimming abilities vary from species to species, further complicating the process of engineering a route to their final destination. In practice, this difference may result in fishway designs that are friendly to some species but may be a hindrance to others.
Final Thoughts
With the deepening of fishway research, more and more design plans have been implemented. However, can all these efforts make fish travel more smoothly? And how many fish will actually successfully reach their destination?
