Estimating Migratory Behavior and Age for Anadromous Coastal Cutthroat Trout in South Puget Sound: Evaluation of Approaches Based on Fish Scales versus Otoliths

Abstract

AbstractImportant variability exists in life history attributes among localized populations of Coastal Cutthroat Trout Oncorhynchus clarkii clarkii in relation to geographic and environmental factors. Describing the life history of locally adapted populations is critical to successful fishery management and conservation. The number of annuli and distance between circuli in scales (i.e., scale analysis) are often used to describe migratory behavior and age of Coastal Cutthroat Trout, but the accuracy of these estimates is largely unknown. In this study, we compared estimates of age (based on analyses of scale and otolith structure) and migratory patterns (based on scale structure and otolith structure and chemistry) for anadromous Coastal Cutthroat Trout in South Puget Sound, Washington State. We compared 48 paired scale and otolith samples (age range = 1–5 years), and age estimates agreed 79% of the time (average percent error [APE] = 5%; CV = 6%), supporting historical age estimates that were generated using scales. However, the number of migrations between freshwater and marine environments estimated using scales and otoliths agreed 44% of the time (n = 50; APE = 25%; CV = 35%). Comparisons of scales and otoliths indicated that more individuals overwinter in marine waters than previously thought based on scale analysis. The majority of fish in this study (68%) were the progeny of females that matured in marine waters and may be vulnerable to fisheries in the marine environment. Current management actions that prohibit the harvest of Coastal Cutthroat Trout in marine waters may be important for the conservation of small localized populations in South Puget Sound.