Efficacy of a Short‐Term Captive Broodstock Program Compared with Hatchery‐Origin Spring Chinook Salmon Derived from the Same Population

Abstract

We examined the efficacy of a one‐generation (five brood years: 1997–2001) captive broodstock program for spring Chinook Salmon Oncorhynchus tshawytscha by comparing survival rates of captive broodstock progeny (CBP; F2) with that of hatchery‐origin fish (HOR) from a conservation hatchery supplementation program in which both groups were derived from the Tucannon River (Washington State) population for the 2000–2006 brood years. Survival rates compared were egg to fry, fry to smolt, egg to smolt, total (ages 3–5) and adult (ages 4+) smolt‐to‐adult‐return (SAR) survival, and total (ages 3–5) and adult (ages 4+) progeny‐to‐parent (P:P) ratio. Total escapement and adult P:P ratios were also examined to determine if observed demographic benefits to the population continued after the captive broodstock program ended. The CBP group had lower within‐hatchery survival than the HOR group, with significant differences in survival at the egg‐to‐fry and egg‐to‐smolt stages due to poor egg viability. Mean untransformed total and adult SARs for the CBP were half those of the HOR group; however, SARs did not differ significantly. The CBP also had significantly lower total and adult P:P ratios than the HOR group and were below replacement for six of the seven brood years. While the captive broodstock provided additional fish for release that would not have been available otherwise, overall the CBP performed poorly and below expectations compared with the HOR group, both within the hatchery and after release. The captive broodstock program provided a short‐term demographic boost, most notable in the 2008–2010 return years, but the benefit did not carry over after the program ended.