Hatchery and Wild Spring Chinook Jack Production in the Upper Yakima

Recently, concern has been expressed about the proportion of early maturing age 3 males, called jacks, returning in the Columbia River basin. In upper Yakima River spring Chinook, jacks return at significantly higher rates in hatchery origin fish than in the naturally spawning population. Over broodyears 1997 to 1999, hatchery jack returns averaged 10%, but then abruptly jumped to an average of 23% over the next 6 broodyears. Natural origin jacks returned at less than half the recent hatchery proportion (mean= 11% over BYs 1997-2005) and showed no significant temporal trend. Thus, as hatchery production increases, making up a larger proportion of the total production, the mean proportion of jacks produced increases. However, we found no significant correlation between the proportion of jacks used as hatchery broodstock and the subsequent proportion of jacks produced by a cohort (p=0.21) nor between the proportion of jacks allowed to spawn naturally and the proportion of jacks naturally produced (p=0.09). Thus, the risk of significantly affecting future jack production rates through either broodstock spawning protocols or management of natural spawners appears very low over the range of jack proportions we observed naturally spawning (4 to 50%) or used as hatchery broodstock (6 to 29%).