Abundance and Survival of Juvenile Spring Chinook Salmon in the Chiwawa River, Washington

Spring Chinook salmon Oncorhynchus tshawytscha typically spawn in smaller tributaries within a watershed compared to other races of Chinook. Spring Chinook are considered “stream type” Chinook that reside in freshwater for a period of up to 15 months before migrating to the ocean.  After emergence from the gravel, juvenile spring Chinook may emigrate from their natal stream to a larger river at any time during their 15 months in freshwater.  Annual variation in the magnitude of these migrations confound comparisons of abundance across years because fish may emigrate from their natal stream at various life stages.  Hence, an estimate of abundance at the smolt stage is not possible.  The Chiwawa River is the single largest spring Chinook spawning tributary in the Wenatchee Basin.  Juvenile abundance monitoring by means of rotary smolt trapping and snorkel surveys and adult monitoring via census redd counts have been ongoing since 1993 and 1990, respectively.  Abundance estimates produced from these activities were used to develop models of capacity at different life stages within the Chiwawa River as wells as life stage specific survival models that provided a method to estimate the number of smolts that emigrated to the ocean.