Understanding the Increased Abundance in Adult Returns for Snake River Sockeye Salmon: The Influence of a Smolt Component to the Program

Snake River sockeye salmon Oncorhynchus nerka were listed as endangered in 1991.  Prior to listing, a captive broodstock program was initiated to prevent species extinction and to begin rebuilding the population.  However, this program has never been identified as a species recovery program. It was termed a “genetic conservation program” and tasked with minimizing the loss of genetic diversity and inbreeding until other factors affecting recovery could be addressed. As the program has evolved into a recovery program, we have slowly ramped up production of smolt releases.  Following increased production, all monitored release strategies (adult release production, egg box, and pre-smolt releases) have shown an increase in survival from the Stanley Basin to Lower Granite Dam. Unlike Chinook salmon and steelhead (that have a long outmigration season, 1-2 months), sockeye salmon outmigration is shorter in duration (2-3 weeks in the spring) and the increased numbers could have overwhelmed migration corridor predators, resulting in more fish surviving to Lower Granite Dam (the “safety in numbers” hypothesis). We have also seen a corresponding increase in the number of adults that have returned to the Stanley Basin over the past three years. The goal of the program is to increase production up to approximately 1 million smolts per year.  Future research will focus on characterizing migration and survival for juvenile Snake River sockeye salmon between the upper Salmon River basin and Lower Granite Dam and identifying the influence larger smolt release groups may have on survival rates relative to current release numbers.