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More than 300 years later, not far from the original fish passage on the river, U.S. Geological Survey researchers have been working with dam operators and other collaborators to expand scientific understanding of the impacts of these barriers and dams on migratory fish and how to maximize their opportunities to travel up and down the river and to and from the ocean.
This is happening across the United States, with the USGS providing scientific data to help build and maintain healthy fish populations, which in turn build healthier ecosystems. Fish passage studies conducted by the USGS provide critical information to help create fish passages that allow key species to pass over dams, cross waterways, and complete their migration cycles. These specially designed structures allow fish to bypass blocked waterways, allowing migratory fish to access critical spawning areas, nursery grounds, and other important habitats.
When migratory fish are able to use effectively designed fish passages, it strengthens inland and marine ecosystems, fishing communities, and enhances conservation efforts for these important fish species. This is important because migratory fish are ecologically and economically important in the ocean, with many species spending the majority of their adult lives in the ocean and the majority being born and bred in freshwater habitats.
Spawning season for migratory fish attracts saltwater and freshwater anglers, supporting a sport fishing community that generated nearly 63 million recreational fishing trips in 2016 and added tens of billions of dollars to local economies. Healthy populations of these fish in the ocean are also important to the U.S. commercial fishery, which generated $51 billion in sales for the U.S. economy in 2015, while also providing food for millions of people around the world.
Why are migratory fish important?
In addition to their value for sport and commercial fishing and as an important staple food for human consumption, migratory fishes are also ecologically important to marine and stream environments.
“As a core component of healthy streams and oceans, migratory fish play a vital role in stable ecosystems for many reasons,” said Ted Castro-Santos, a research ecologist at the USGS Leetown Science Center. “The fact that they are a primary food source for so many different species is probably one of their most important roles.”
Adult migratory fish carry nutrients into freshwater habitats, and many of them become prey for other fish, birds, and animals. Fish that are able to reach spawning grounds upstream and successfully reproduce become part of a spawning cycle that can produce trillions of eggs each season.
These eggs nourish nearly every level of the food web, and even with high egg loss rates, potentially millions of young fish hatch each season. Juveniles also serve as a primary food source in freshwater habitats until they are large enough to attempt to make their own way to ocean waters, becoming part of the marine food chain and completing the migratory cycle started by their parents.
But the delicate balance of these migratory cycles has been disrupted as dams and barriers have choked waterways across the country and cut off many migratory fish from their ancestral spawning areas.
How does the USGS Fish Passage Study help?
To help migrating fish move up and down waterways, USGS scientists study fish behavior and use that knowledge to design and develop new and improved fishways, and work with states and other partners to determine the best locations to install fishways. The USGS’s ongoing fishway research is important because man-made barriers can slow or block migration and are one of the reasons fish populations are declining.
“Over time, human-made barriers have been found to be one of the main stressors that have contributed to population declines in many migratory fish species,” said Tom O’Connell, director of the USGS’s Leetown Science Center. “Effective fish passage is a key factor in restoring healthy migratory fish populations.”
USGS research will not only aid species recovery, but also help state resource managers and dam operators because new and improved fish passage technologies can be more cost-effective, allow more fish to complete their migration, and require less time or water, which can save operators money.
Think like a fish
In order to design structures that migratory fish can find and use, it is important to understand their driving forces and how they interact with artificial barriers. USGS scientists study migratory fish to better understand fish behavior so that scientists and engineers can use this knowledge to create more effective fish passages.
Creating effective fish passes is a constant challenge because the size, purpose, and design of dams and barriers change over time. USGS scientists must understand why some fish successfully use fish passes to bypass barriers while others cannot.
“We have a huge variety of fish species, and current technology only allows a small fraction of them to cross the barriers,” Castro-Santos said. “Studying new ways to improve the design and get fish to cross the barriers will help everything related to these ecosystems.”
USGS experts evaluate dam design, barrier use, partner management efforts and fish behavior to tailor different fish passages to needs across the country. Studies of some older fish passage designs found that a significant portion of migratory fish species were unable to use them, often because they couldn’t find the structure’s entrance, Castro-Santos said. This knowledge has led to the development of new techniques to attract fish to passage entrances, such as changing the speed of water in the passage to match the preferences of the target species, simulating certain noises that can lure fish toward the passage, and using pheromones to attract fish.
While most fishways are used to help fish complete their migration cycle over artificial barriers, experts also see a potential use for fishway research as limiting the spread of invasive species upstream or downstream. As the USGS continues to study new and improved methods for getting native fish to migrate upstream, scientists will also look for ways to prevent invasive fish from using these fishways.
One size No Suitable for everyone
Barriers come in all shapes and sizes, and there are dozens of different fish species affected by them, so a single solution for fish passage will not work for all fish in all locations.
“Scientists have made great progress in the last few decades in terms of fish characterization and fish passage design,” O’Connell said. “Most species require passages designed based on their unique body characteristics.”
For example, most migratory fish encounter obstacles when traveling downstream to the sea, such as getting stuck in power-generating turbines, which results in many fish deaths each year. This is especially true for American eels, which spend most of their adult lives in freshwater before swimming to the sea to spawn, which is the opposite of the movement pattern of most migratory fish and may require solutions that may not work for other fish.
“Due to the complexity of the different migratory fish species and their needs, we still have a lot of work to do to improve passage conditions for all species,” Castro-Santos said.
Why not just remove the dam?
There is growing interest in removing dams around the world given the problems caused by man-made barriers. However, most dams provide important services to society, such as power generation, flood control, and reservoir storage, so removing all dams is not a viable option. Designing effective fish passes is one of the best ways to balance human needs and support ecosystems and migratory fish.
“In the future, more dams are likely to be built around the world, not fewer,” said Mona Khalil, energy and wildlife program specialist at the USGS. “Therefore, it is more important than ever to continue studying migratory fish so that the best technology and fish passage designs can be used to help them complete their migratory cycle.”
Castor-Santos believes the fish passage research will have lasting benefits.
“Hopefully, new science and fish passage design will lead to more efficient fish passage,” Castro-Santos said. “Restoring passage to upstream habitats is important — not only for fish, but also for the stream, river and ocean ecosystems these fish inhabit, as well as for the communities, fishermen and world populations that depend on migratory fish.”
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