The results show that young salmon scatter in all directions as they first enter the ocean, which is contrary to previous assumptions that most salmon head north immediately after leaving the Columbia River. "It's becoming clear that the first few weeks after salmon enter the ocean from their freshwater homes is a crucial time," said Geoff McMichael, the PNNL scientist who led the study, which was published recently in Animal Biotelemetry.

"Much of their health and the success of their subsequent runs upstream to start the next generation are dictated by those first few weeks in the ocean. Conditions such as water temperature, food availability and the number of predators are critical. Everything we can learn about salmon behavior during this critical time could help managers restore their stocks more effectively," added McMichael.

The team found that much of the fish's initial behavior and chance of survival were determined by factors beyond anyone's control, such as the movement of ocean currents. Under certain conditions, for instance when the ocean is unusually warm, Pacific hake – a fish that McMichael calls a "voracious predator" – are more likely to come closer to the mouth of the river and feast on salmon.