Salmon swim together in one of the many pools at the Wizard Falls Fish Hatchery in this file photo.

Adult salmon sense when the time is right to leave the ocean and head for fresh water to spawn. But how do they know this? And how will climate change affect this cycle? Rebecca Flitcroft, a research fish biologist with the USDA Forest Service, Pacific Northwest Research Station, and colleagues took a closer look at the connection between migration patterns and stream conditions.

They found that water temperature and the rate of streamflow appear to be two of the environmental conditions that precipitate the migration of salmon to their freshwater spawning grounds. This doesn’t bode well for salmon, given that these stream conditions are being altered by climate change.

The researchers used hydrologic data collected at dams in Oregon and Washington and linked them with data showing the timing of migratory fish passing those dams. The findings are displayed visually in ichthyographs, a newly developed graphic tool that shows the precise conditions under which fish move upstream.

This research provides a current baseline for understanding the connection between hydrologic conditions and fish movement. It also highlights ways in which the effects of climate change potentially could be mitigated by managing streamflows at critical times of the year to benefit salmon migration.

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