Steel, Ashley. 1999. Instream factors affecting juvenile chinook salmon migration. Ph.D.
Juvenile chinook salmon, Oncorhynchus tshawytscha, migration is regulated by a host of both physiological and environmental variables. This research investigates the effects of three environmental variables (flow, temperature and water clarity) on migration patterns. A combination of mathematical and statistical models were used to investigate two datasets on juvenile chinook salmon migration: radio telemetry data from the Grande Ronde and Snake Rivers and in-stream capture rate data from the Skagit River. Using the radio-telemetry data, a two-state Markov chain model was developed to estimate parameters that describe unobservable fish behavior. The model provides a method for comparing migratory behavior across species, watersheds, or seasons. The same fisheries data was then combined with data on water flow, temperature, and clarity to assess the impact of in-stream factors on fish travel speed and migration timing. Fish traveled faster in the clear, upstream waters than in the slower-moving, murky waters downstream. Most migration occurred at night; mid-day movements were much more common with reduced water clarity. Similar patterns were detected for wild, chinook salmon on the Skagit River. More fish were captured when visibility was low than when visibility was high. Water temperature was not a significant factor in explaining migration patterns for either analysis. In conjunction with the fisheries research, horizontal viewing discs for measuring water clarity were evaluated and found to be a good, inexpensive measure that can be used in a wide variety of situations.