Every Fall the Salmon River in Idaho fills with thousands of sockeye salmon swimming upstream to breed. But, in recent years, their numbers have been drastically reduced. I’m Jim Metzner, and this is the Pulse of the Planet, presented by the American Museum of Natural History.
Sylvia Hamilton is a field technician for the Idaho Department of Fish and Game. Standing next to a weir, or trap used to count and then release these fish, she tells us that dams built along the river may be interfering with the sockeye salmon migration.
This weir was placed in the stream in the 50’s to monitor sockeye returns. And they captured about 6,000 or so sockeye. Since then, the final four dams have been placed on the river and the returning numbers of sockeye have declined drastically since then. There were thousands before and now there’s individuals: less than ten, sometimes none.”
At the dams, a combination of disease, predators and currents can spell death for a migrating salmon.
“The fish don’t seem to be making it through the dams for several reasons. One of the reasons is because when they’re migrating out to the ocean, they’ll inflate their swim bladders and they’ll float down with the high run off. So they’re not actively swimming. When they reach the dams, they hit slack water, and so instead of an active current, they are in more of the lake system. So they have to find their way; they get lost. They become preyed upon by other fish and birds. They’re very susceptible to diseases.”
One strategy for saving the salmon has been to transport them in barges around the dams. However scientist still aren’t sure whether this project has been successful.
Additional funding for Pulse of the Planet has been provided by the National Science Foundation. I’m Jim Metzner