Evaluation of the relationship among time of ocean entry, physical and biological characteristics of the estuary and plume environment, and adult return rates, 2003

This study examines the relationship between smolt-to-adult return rates (SARs) for spring chinook salmon and the time of ocean entry and physical and biological characteristics of the estuary and nearshore ocean plume environment. Study fish were reared by the Clatsop Economic Development Committee Fisheries Project in the lower Columbia River. During 2003, the second year of releases, six groups of yearling spring chinook salmon were transferred from Willamette Hatchery to net pens in Blind Slough in the Columbia River estuary, reared for 14 days, and released at 10-day intervals from 9 April through 27 May. Size and smolt development (gill Na+-K+ ATPase activity) at release were similar among groups. Mortality at Willamette Hatchery and in Blind Slough was higher than usual for all groups, although no causative viral, bacterial, or parasitic agents were identified. Coded-wire-tags will be recovered from adults beginning in 2004 from the Blind Slough terminal gill net fishery. Contract no. W66QKZ20374368