Quantifying migratory capacity and dispersal of the invasive tench (Tinca tinca) in the St. Lawrence River using otolith chemistry

The study of distribution and dispersal of invasive fishes is challenging during the early stages of invasion. Quantification of trace elements incorporated into fish hard parts represents an innovative technique for this task. Otolith chemistry has been used to describe fish stock structure, migratory behaviour and to support the management of several species. We used otolith chemistry to study the dispersal and population structure of tench (Tinca tinca), an invader in the St. Lawrence River. Tench movements throughout the invaded portion of the system were reconstructed using a Random Forests algorithm. The results showed that, despite the presumed limited dispersal capacity of the species, tench are capable of extensive migratory movements (up to 250 km). The variability in migratory patterns among individuals, including both short- and long-distance movements, supports a stratified diffusion. Such a strategy may explain the successful invasion of tench in the St. Lawrence River ecosystem. Our study represents a flexible framework for the study of tench ecology in its invaded and native range, as well as for other freshwater invasive fishes.