Juvenile Chinook and coho growth, diet, and size-selective mortality

Investigator: Dave Beauchamp (USGS)

Size-selective mortality has been widely reported during the juvenile stages of many species in marine environments and can be the predominant force affecting marine survival and adult abundance. Strong size-selective mortality has been reported for most species of Pacific salmon during their early marine phase. Evidence of strong size-selective mortality for hatchery Chinook salmon in Puget Sound and coho salmon in the Strait of Georgia has linked higher adult returns to larger sizes achieved during early months of marine life, highlighting the importance of understanding the relationship between early marine growth periods and overall marine survival. This relationship likely varies over time and by life stage, life history type, or geographic area.

This project compares the scale-based growth patterns of the juvenile Chinook and coho sampled during outmigration years 2014 and 2015 with the juvenile growth patterns of the adult Chinook and coho that survived to return from these cohorts. From this analysis, project investigators can determine the magnitude of size-selective mortality based on stage-specific growth and identify the periods and conditions when growth or size of the juveniles that survived to adulthood diverged from the remainder of the juvenile population. Additionally, the early marine diet composition of coho will be examined to determine the critical prey sources fueling their growth, diet overlap, and potential for competition with juvenile Chinook and other juvenile salmon, herring, and forage fishes. This work will further our understanding of the critical periods and underlying processes that influence marine survival of Chinook and coho salmon in Puget Sound.

Juvenile Chinook salmon in a purse seine net.