Straying of brown trout in the catchment of a large New Zealand river evaluated by otolith microchemistry

Natal homing and straying are behavioural tactics of migratory animals that return to nursery habitats to breed as adults. Straying has evolutionary and ecological importance for species flexibility, interpopulation connectivity and success of invasive species in new environments. This study aimed to estimate the relative importance of straying and homing in introduced brown trout Salmo trutta spawning in a model coastal tributary (Silverstream) of a large New Zealand river using otolith microchemistry. The data on natal homing and straying are important for the understanding of the ecological resilience of salmonid populations and metapopulations, and the development of effective management measures at stream or catchment scales. To examine brown trout homing and straying in a river catchment, otolith microchemical analysis was applied. We used linear discriminant function analysis to compare the trace element composition in the otoliths of YoY (young‐of‐the‐year) trout collected at spawning streams across the catchment and adult trout reproducing in Silverstream. The results showed that only six from a sample of 30 spawning adults in Silverstream originated from Silverstream. Another 14 fish likely originated from other Taieri tributaries further upstream, but the origin of the remaining 10 could not be determined. Contrary to published studies based on wild populations of brown trout in Europe, and several other species of salmonids, a large proportion of brown trout spawners collected in Silverstream were strays. The large number of strayers identified in Silverstream may be a consequence of the geomorphology of the Taieri catchment and highlights the adaptability of brown trout to different environmental contexts.