The role of temperature and flow on the migration of Chinook salmon (Oncorhynchus tshawytscha) smolts.

For salmonids, the smolting process includes substantial morphological, physiological and behavioral changes all of which must coincide to ensure the greatest chance of survival in the marine environment. Therefore, understanding how environmental parameters influence the onset, duration, and termination of smolting can have substantial management implications. I used historical data and a controlled laboratory experiment to investigate the role of both temperature and flow on the timing of migration in Chinook salmon (Oncorhynchus tshawytscha) smolts. An Information Theoretic Model Comparison (ITMC) technique was used to correlate 13 years of historical smolt migration data from the Nechako River in central British Columbia, Canada with data on temperature and discharge from the same period. A combination of temperature experience (accumulated thermal units ATU) and flow discharge were best able to describe the observed migration patterns. In addition, ATU consistently performed better than daily mean temperature suggesting that temperature experience plays a larger role in the migration process than a temperature threshold. In a laboratory experiment, temperature manipulation affected growth and development of physiological smolt characteristics. In addition, fish in tanks with increasing temperature showed earlier movement than those in constant temperature tanks. Flow velocity was not found to have an effect on physiological development of smolt characteristics and did not appear to affect timing of migration in the absence of increasing temperature. However, velocity did influence the pattern of migration, since the presence of a strong, directional flow resulted in a well defined migration event with a clear increase, peak and decrease in movement regardless of the temperature manipulation. Alternatively, fish in experimental tanks without increased flow showed either pulses of movement or no clearly defined movement period. A model similar to the approach for the historical data was used to assess the mo