Evidence for multiple navigational sensory capabilities by Chinook salmon

To study the complex coastal migrations patterns exhibited by juvenile Columbia River Chinook salmon as they enter and move through the marine environment, we created an individual-based model in a coupled Eulerian-Lagrangian framework. We modeled five distinct migration strategies and compared the resulting spatial distributions to catch data collected during May and June in three years. Two strategies produced fish distributions similar to those observed in May but only one also produced the observed June distributions. In both strategies, salmon distinguish North from South (i.e., they have a compass sense) and they control their position relative to particular landmarks, such as the river mouth. With these two abilities, we posit that salmon follow spatially-explicit behavior rules that prevent entrapment in strong southward currents and advection offshore. Additionally, the consistent spatio-temporal distributions observed among years suggest that salmon use a clock sense to adjust their swim speed, within and among years, in response to progress along their migration.