Ontogenetic shifts in growth and habitat use of freshwater Coastal Cutthroat Trout revealed through otolith analysis of multiple elements

Otolith microchemistry is a widely used tool in fisheries research to determine migration patterns, stock structure, and variation in habitat utilization. This study combined multiple analytical methods to determine fine-scale ontogenetic shifts. Variability in Manganese and Zinc were used to assess freshwater habitat movements and age and size at lake entrance. Furthermore, a suite of elements was used to assign lake-based (i.e., captured) coastal cutthroat trout to their natal tributaries of origin. Coastal cutthroat trout entered the lake at a mean fork length of 107.8 (31.8 SD) mm and, on average, at age 2 (49%). A linear discriminant function model successfully assigned 71% (101/142) of the cutthroat trout captured in Comox Lake to their natal tributaries. Among the five assessed, two tributaries disproportionately contributed to the lake-based population (58%). This study clarifies patterns of life history diversity and natal origin of lake-based cutthroat trout and validates the use of Manganese and Zinc to determine ontogenetic changes in growth, likely indicative of a changing environment and age at time of event, for a freshwater species.