Distribution and straying of minijack Chinook Salmon released from a captive broodstock hatchery program

Abstract

AbstractObjectiveProduction of Chinook Salmon Oncorhynchus tshawytscha in hatcheries can unintentionally produce large numbers of age‐1 males, termed "minijacks," which pose ecological and genetic risks to target and nontarget populations. We evaluated the postrelease distribution of minijacks produced in a hatchery captive broodstock program targeting the White River in the Columbia River basin between 2010 and 2015.MethodsFish were passive integrated transponder (PIT)‐tagged in the hatchery (n = 218,555), and databases were searched to determine movement behavior and final detections on fixed PIT tag antenna arrays during the year in which they were released.ResultTwo main movement behaviors were detected: (1) residuals, which moved solely within the subbasin of release; and (2) migrants, which moved downstream into the Columbia River and then reascended the Columbia River in the year of release. Minijacks that reascended fish ladders in the Columbia River were most often detected at Rock Island and Bonneville dams, the nearest and furthest detection locations downstream of the Wenatchee River. Minijacks were last detected in all locations where spring Chinook Salmon spawn in the Wenatchee River subbasin (seven tributaries and one main‐stem area) and also in the Entiat River (an adjacent watershed); minijacks in eight of the nine locations were considered strays. Estimates of minijacks that strayed outside of the White River were between 61% and 100% annually and were influenced by release location. Minijacks were also more abundant than males of all older ages in some of the tributaries during some years. In addition, they were detected in these tributaries during periods when anadromous adults migrate into spawning areas and when spring Chinook Salmon spawn.ConclusionThe large amount of minijack production and the spatial and temporal overlap could pose genetic and ecological risks to both target and nontarget populations and particularly high straying poses risks to the maintenance of between‐population genetic variability.