Physiological condition and salinity preference in freshwater migrating juvenile sockeye salmon

<p>The amount of time that juvenile salmon remain in an estuary varies among and within populations, with some individuals passing through their estuary in hours while others remain in the estuary for several months. Underlying differences in individual physiological condition, such as body size, stored energy, and osmoregulatory function, could drive individual variation in the selection of estuary habitat. Here we investigated the role of variation in physiological condition on the selection of estuarine and ocean habitat by sockeye salmon (<em>Oncorhynchus nerka</em>) smolts intercepted at the initiation of their 650 km downstream migration from Chilko Lake, Fraser River, British Columbia (B.C.). Behavioural salinity preference experiments were conducted on unfed smolts held in fresh water at three time intervals during their downstream migration period, representing the stage of migration at lake exit, and the expected timing for estuary entry, and ocean entry (0, 1, and 3 weeks after lake exit, respectively).</p>