Coastal Stocks of Oregon Chinook Salmon: Precision, Accuracy, and Trends in Age Estimates

Coastal stocks of Chinook Salmon in Oregon support substantial commercial and recreational harvest opportunities from Oregon to Alaska, thereby infusing money into local economies.  To enable adequate harvest allocation while meeting conservation goals, reliable age estimates of fish escaping to the spawning grounds are needed to populate models to forecast abundance.  In Oregon, age estimates for Chinook Salmon are derived from scales.  Fish scales are often viewed as “inferior” for ageing by biologists.  However, scales are ideal for ageing salmonids because they are a short-lived, coolwater species; scales are easily sampled and thereby allow statistically-robust sample sizes; and they provide reliable age estimates.  Rigorous ageing protocols are used to maintain precision, and accuracy is measured by blind reads of scale samples from tagged hatchery fish of known age.  Here, we examine trends of age estimates from scale samples of Chinook Salmon collected during spawning ground surveys in eight Oregon coastal basins over 25 years.