| For salmonids, the smolting process includes substantial morphological, physiological and behavioural changes all of which must coincide to ensure the greatest chance of survival in the marine environment. I used historical data and a controlled laboratory experiment to investigate the role of both temperature and flow on the migration of Chinook salmon ( Oncorhynchus tshawytscha) smolts. 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, fish in tanks with increasing temperature showed an earlier physiological and behavioural response than those in constant temperature tanks. Flow velocity had an effect on the pattern of migration but not on the onset of movement or on the physiological changes. Failure to consider both parameters when making management decisions or manipulating one independent of the other can have an impact on when fish begin migrating as well as on the migration pattern. |
