The toughest journey to home: Dams block salmon migration and hurt the ecosystem

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A recent UW study published in Nature suggests man-made blockades are damaging the biodiversity in rivers.

The research shows that among the 246 longest rivers in the world, only one-third of them remain free-flowing today. Constructions of dams and reservoirs significantly influence the flow of rivers, directly causing connectivity loss.

Free flowing rivers are essential to the health of the natural environment. Water, energy, and living species are exchanged in the process of flowing, ensuring the normal function of the ecosystem.

“Those movements of material and energy and organisms are kind of the basis for the ecosystem functions,” Gordon Holtgrieve, an assistant professor at the UW School of Aquatic and Fishery Sciences, said. “And those ecosystem functions are the base services we depend on.”

Dams and reservoirs change how water flows down rivers. When the flow of water is altered, it interacts differently with ecosystems. In the Pacific Northwest, salmon habitats are being threatened by these changes.

Pacific salmon are known for their long-distance migration between rivers and the ocean. They travel hundreds of miles from the home stream to the ocean. After several years, they return to their birthplace and spawn. Dams physically block their pathways, which increases their mortality rates and reduces how successful reproduction is.

“Dams have impacts on salmon’s downstream and upstream migration,” Nora Nickum, ocean policy manager at Seattle Aquarium, said. “They slow down the migration, young salmon spend more energy going downstream, and it makes the migration more difficult for them.”

Nickum also mentioned that the temperature of water increases behind dams during the summer months due to decreased water flow. Changes in temperature increase disease and death in the salmon population, which rely on specific water temperatures to maintain their metabolism, much like humans.

Salmon is a crucial species to the ecosystem. Holtgrieve said salmon and their eggs feed 130 to 140 species along their migration route including birds, bears, insects, and humans. The loss in salmon would cause severe damage to biodiversity and lead to degradation of the habitat.

Salmon also has important economic and cultural values. A large number of people earn a livelihood by fishing. Seattle residents, Native Americans, and many other populations have a strong cultural association with salmon.

To preserve the salmon population and their migration, multiple solutions are put into practice, including fish ladders and salmon hatcheries.

According to Holtgrieve, these practices are not always successful. Hatchery-bred salmon have less resistance to parasites and are therefore less likely to survive in the natural environment.

On the other hand, dams provide clean energy, which helps prevent further climate change.

“We have access to relatively cheap power that is low carbon but not zero carbon,” Holtgrieve said. “It is a cleaner form of energy with respect to carbon and climate change. That is an important thing. That supports industry and people’s lives. ”

Luckily, some dams are relatively small and old. They do not produce a lot of energy and their removal is expected to be relatively easy for policymakers to get behind.

Finding the government money to fund the projects, however, remains a challenge.

There are things we can do to address this problem as students and as a community. Choosing sustainable seafood and supporting sustainable fishing can be very helpful. Also, it is always important to keep carbon reduction and energy consumption in mind.

“If we can reduce our need for hydroelectric power sufficiently, then we don’t need those dams,” Holtgrieve said. “The tradeoffs become very easy.”

As both Holtgreive and Nickum said, it is crucial for us to speak up and let the policymakers know our preferences on this issue so they can incorporate our thoughts into their decisions.

Reach contributing writer Sunny Wang at Twitter: @sunnyqwang64

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