Age analysis for 22 years (1980 excluded) showed that the overall percentages for female spawners was 53% (4-year olds), 38% (3-year olds), and 9% (5-year olds). The age composition of male spawners showed a high degree of variability throughout the study. Male chinook of age 2, 3 and 4 were dominant annually, but 5- and 6- year old fish were present in most spawning seasons. All chinook carcasses from which scales were collected were also measured for length (over 120 samples in 22 years). Decreases in mean length were documented for all age classes for each of the El Nino episodes that occurred during the study (1982-1984; 1992-1993; 1997-1998). The decreases in mean length appeared to carry forward for each cohort's age class. The total number of chinook redds was tabulated by counting "fresh" redds during weekly spawning surveys. The mean number of redds was 117 for the 23-year period with a mean of 0.9 redds per adult salmon or 1.8 redds per female.

The Hanford Reach of the Columbia River provides the only major spawning habitat for the upriver bright (URB) race of fall chinook salmon in the mainstem Columbia River. Hanford Site biologists have conducted aerial surveys of spawning salmon in the Hanford Reach since 1948. This report summarizes data on fall chinook salmon spawning in the Hanford Reach and presents a discussion of factors that may affect population trends. Most data are limited to fisheries agency reports and other working documents. Fisheries management practices in the Columbia River system have changed rapidly over the last decade, particularly under requirements of the Pacific Northwest Power Planning and Conservation Act of 1980. New information has been generated and included in this report. 75 refs., 17 figs., 11 tabs.