The Comparative Survival Study began in 1996 with the objective of establishing a long-term data set of annual estimates of the survival probability of generations of salmon from their outmigration as smolts to their return to freshwater as adults to spawn (smolt-to-adult return rate; SAR). The study was implemented to address the question of whether collecting juvenile fish at dams, transporting them downstream of Bonneville Dam (BON), and then releasing them was compensating for the effect of the Federal Columbia River Power System (FCRPS) on the survival of Snake Basin spring/summer Chinook salmon that migrate through the hydro-system.