Growth-increment formation using otoliths and scales of juvenile chinook salmon

Abstract

Freshwater growth of juvenile Chinook salmon Oncorhynchus tshawytscha influences survival and recruitment to the adult population. Retrospective analysis is used to measure salmon growth at previous ages, with fish size and growth assumed to be accurately reflected by otolith increments and scale circuli. I conducted a 122-d laboratory experiment to validate the relationship among body size, growth, and width to daily otolith growth increments and scale circuli in juvenile stream-type Chinook salmon. Fish total length was found to be proportional to otolith axis length (r² = 0.209, p < 0.001), otolith diameter (r² = 0.667, p < 0.001), and scale radius (r² = 0.538, p < 0.001). Somatic growth was accurately reflected by growth in otolith axis length (r² 0.65, p < 0.001) and growth in scale radius (r² = 0.449, p < 0.001). My study validated the assumption that fish body size and growth are reflected by otolith and scale size and growth- increment formation. The findings of my study can be used to ascertain body size at previous ages, which will help managers detect threshold sizes, examine the strength of size-selective mortality, and determine how growth rate affects smolt migration, early marine survival, and duration of ocean residency.