Pacific Or Bust: Fingerling Chinook salmon are dumped into a holding pen Tuesday as they are transferred from a truck into the Sacramento River in Rio Vista, Calif. From here, they'll be towed downstream for a bit, then make their own way out to the Pacific Ocean. Justin Sullivan/Getty Images hide caption

itoggle caption Justin Sullivan/Getty Images

Bright red sockeye salmon swim up the Fraser River to the stream where they were hatched. Current Biology, Putman et al. hide caption

itoggle caption Current Biology, Putman et al.