Summary

Description

Upriver movements were determined for Chinook salmon Oncorhynchus tshawytscha returning to the Yukon River, a large, relatively pristine river basin. A total of 2,860 fish were radio tagged during 2002-2004, and 2,790 fish (98%) tracked upriver. Most fish exhibited continual upriver movements and strong fidelity to the terminal tributaries entered, with only a small percentage (2.5%) deviating from this pattern. Average movement rates were substantially slower for fish spawning in lower river tributaries (28-40 km d-1) compared to upper basin stocks (52-62 km d-1). Three distinct migratory patterns were observed, including a gradual decline, pronounced decline, and substantial increase in movement rate as the fish moved upriver. Stocks destined for the same region exhibited similar migratory patterns. Migratory patterns among individual fish within a stock showed substantial variation, but tended to reflect the regional pattern. Differences between consistently faster and slower fish explained 74% of the within-stock variation, whereas relative shifts in sequential movement rates between hares (faster fish becoming slower) and tortoises (slow but steady fish) explained 22% of the variation. Pulses of fish moving upriver were not cohesive. Fish tagged over a 4-day period took 14 and 16 d to pass tracking station sites 580 and 872 km upriver, respectively. Movement data provided valuable insights into the run dynamics of the return, but individual variation among fish complicates efforts to manage in-river fisheries. The diverse migratory patterns exhibited by the fish also suggest that movement studies based on small numbers of individuals may not adequately reflect the patterns exhibited by the larger population. Movement rates were substantially faster and the percentage of atypical movements considerably less than reported in more southern drainages, but may also reflect the pristine conditions within the Yukon River, wild origins of the fish, and relatively discrete run timing of the returns.