Evaluating Abundance “Boosts” from a Chinook Salmon Supplementation Program

Since 1998, the Nez Perce Tribe of Idaho has supplemented the Johnson Creek natural summer Chinook spawning aggregate with hatchery-reared Chinook.  The Tribe’s Johnson Creek supplementation program adheres to a strategy designed to artificially stimulate an increase in natural origin spawner abundance by augmenting the total number of spawners on the spawning ground.  Thus far, the relative success of the program has been inferred using within-stream, origin-specific paired comparisons of abundance and productivity and through genetic comparisons of relative reproductive success.  More recently, we evaluated the efficacy of supplementation to provide a demographic boost in Johnson Creek using temporally based statistical comparisons of total and natural origin abundance.  Examining abundance shifts across pre- and post-supplementation periods in contrast to ten comparable, yet untreated, reference populations allowed for fluctuating environmental conditions while judging program success.  Our results indicate Johnson Creek supplementation provided abundance boosts to both total and natural origin only returns.