Rainbow trout (Salmo gairdneri) entering and leaving inlet and outlet spawning streams were trapped and marked during three years. Spawners entered the outlet stream at approximately the same time each year despite considerable differences in time of lake ice breakup. Spawners entered the inlet stream 3 to 5 weeks later than outlet spawners and at water temperatures several degrees higher. The inlet spawning run was later in years when disappearance of lake ice was delayed. Comparative statistics are presented on size, sex ratio, survival and diel movement of spawners in both streams. Effects of several types of marking were compared; removal of adipose fins produced much lower mortality than tagging with Petersen discs. In the outlet stream an inverse correlation existed between number of spawners and survival, condition, and length of stay of spawners in the stream. Factors which may be responsible for differences in timing of spawning migrations are discussed.
Local variation in the timing and advancement of lake ice breakup and impacts on settling dynamics in a migratory waterbird
