Atlantic salmon (Salmo salar L.) kelt rheotaxis and position choice are influenced by flow velocity and turbulence in a regulated river

The migratory behaviour of Atlantic salmon kelts is poorly understood. Due to the Atlantic salmon's considerable socio-economic and ecological importance, their precipitous population abundance declines, and the population resilience potential of salmon kelts, addressing these knowledge gaps is important. In this study, directional swimming behaviours and position choice were quantified for the swimming trajectories of 48 acoustically tagged kelts in a regulated river. The kelts exhibited positive rheotaxis under high flow velocities, though their response to turbulence was more varied. The kelts exhibited clear preferences for moving between positions with similar hydraulic conditions and avoided moving to positions where the flow velocity or turbulence changed rapidly. The extent to which the kelts avoided moving to positions with rapid changes in hydraulic conditions varied by individual experience, individual body size, how active the individual was during daytime and how often an individual was detected near a conspecific. This study is the first to combine data on intrinsic individual characteristics with extrinsic hydraulic factors to conduct a detailed analysis of kelt behaviour during migration in a regulated river. By examining these behaviours across different hydraulic conditions, our findings bear important implications for both hydropower development and river management practices.