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Accurate estimates of escapement by adult anadromous salmonids are difficult, especially in large, multistock river systems. We used radiotelemetry and a fishery reward program to calculate escapement, harvest, and unaccounted for loss rates for 10 498 adult chinook salmon (Oncorhynchus tshawytscha) and 5324 steelhead (Oncorhynchus mykiss) during six return years in the Columbia River basin. Mean annual escapements to spawning sites, hatcheries, or the upper bounds of the monitored hydrosystem were 73.4% (spring-summer chinook salmon), 61.3% (fall chinook salmon), and 62.6% (steelhead). Mean reported harvest rates were 8.7% (spring-summer chinook), 22.0% (fall chinook), and 15.1% (steelhead) within the mainstem hydrosystem and 5.9%, 3.4%, and 5.7%, respectively, in lower hydrosystem tributaries. On average, 12%-17% of each run had unknown fates in the mainstem hydrosystem. Escapement, harvest, and loss varied significantly between runs and years, within runs between known-origin subbasin stocks, and between interdam river reaches. Multiyear quantitative assessments like this can reduce uncertainty, clarify inter- and intra-annual variability, and help managers better evaluate fisheries, identify conservation priorities, and help protect evolutionarily significant populations. Resume : Il est difficile d'estimer avec precision les echappements des salmonides adultes, particulierement dans les grands reseaux hydrographiques qui contiennent plusieurs stocks. Nous avons utilise la radiotelemetrie et un pro- gramme de peche avec recompenses pour calculer l'echappement, les captures et les taux de pertes inexpliquees pour 10 498 saumons quinnat adultes (Oncorhynchus tshawytscha) et 5324 truites arc-en-ciel anadromes (Oncorhynchus my- kiss) durant six annees de montaison dans le bassin hydrographique du fleuve Columbia. Les echappements annuels moyens vers les sites de fraie, les piscicultures et les limites superieures du systeme hydrographique sous surveillance sont de 73,4 % (saumons quinnat de printemps et d'ete), 61,3 % (saumons quinnat d'automne) et 62,6 % (truites arc- en-ciel anadromes). Les taux moyens de captures signalees sont de 8,7 % (saumons quinnat de printemps et d'ete), 22,0 % (saumons quinnat d'automne) et 15,1 % (truites arc-en-ciel anadromes) dans le cours principal et respective- ment de 5,9, 3,4 et 5,7 % dans les tributaires du cours inferieur. En moyenne, le sort de 12-17 % des poissons de chaque montaison reste inconnu dans le cours principal. L'echappement, la capture et la perte varient significativement d'une montaison a une autre et d'une annee a l'autre; ils varient aussi au sein d'une meme montaison parmi les stocks identifies comme provenant de divers sous-bassins, de meme que dans les divers troncons de riviere entre les barrages. Des estimations comme les notres qui couvrent plusieurs annees peuvent reduire l'incertitude, preciser la variation an- nuelle et inter-annuelle et aider les gestionnaires a mieux evaluer les peches, fixer les objectifs prioritaires de conserva- tion et proteger les populations d'importance evolutive.

An understanding of the migration timing patterns of Pacific salmon Oncorhynchus spp. and steelhead O. mykiss is important for managing complex mixed-stock fisheries and preserving genetic and life history diversity. We examined adult return timing for 3,317 radio-tagged fish from 38 stocks of Columbia River basin spring–summer Chinook salmon O. tshawytscha over 5 years. Stock composition varied widely within and between years depending on the strength of influential populations. Most individual stocks migrated at similar times each year relative to overall runs, supporting the hypotheses that run timing is predictable, is at least partially due to genetic adaptation, and can be used to differentiate between some conspecific populations. Arrival timing of both aggregated radio-tagged stocks and annual runs was strongly correlated with river discharge; stocks arrived earlier at Bonneville Dam and at upstream dams in years with low discharge. Migration timing analyses identified many between-stock ...