Correspondence between scale growth, feeding conditions, and survival of adult Chinook salmon returning to Puget Sound and coastal Washington: Implications for forecasting

In this study, we used scale analysis of returning adults to examine the relationship between early marine growth and survival for Chinook salmon (Oncorhynchus tshawytscha) returning to the Puget Sound and coastal Washington, USA. In total, we examined scales from 2604 individuals from 5 stocks over 7 outmigration years characterized by a range of survival conditions (range from 0.11 to 9.50%). We observed a positive relationship between growth during the first year at sea and survival for adults returning to Puget Sound and the Washington coast. Scale growth during the first year at sea did not co-vary between coastal Washington and Puget Sound stocks, and in most years coastal Chinook salmon attained a larger size at the end of the first year at sea. Large scale oceanographic variables (PDO, NPGO) were not significantly related to variation in scale growth, but for some Puget Sound populations, scale growth was higher in years of cooler sea surface temperatures and lower Pink salmon (O. gorbuscha) abundance. We developed a biological indicator for forecasting cohort survival of Tumwater Falls hatchery Chinook salmon on the Deschutes River, WA using marine growth estimates of the earliest returning fish (age-21). The marine growth index predicted survival better for 8 brood years compared to a recent 5 year average returns forecasting approach (3.40% vs 35.41% Mean Percent Error). Results from this study suggest that early marine growth is important to the survival of Puget Sound and coastal Washington Chinook salmon and may be a useful biological indicator to improve pre-season forecasting of Chinook salmon populations in Washington State.