Associate Professor Carleton University Ottawa, Ontario, Canada
As global freshwater biodiversity continues to deteriorate rapidly, it is critical that system-specific conservation actions are identified and implemented. In interconnected freshwater systems like waterways and canals, key threats to biodiversity include river fragmentation and connectivity loss, and the diffusion of invasive species. Managing anthropogenic barrier (e.g., navigation locks, dams) connectivity in waterways to selectively allow and restrict passage of native and invasive species, respectively, is a major global challenge. The Rideau Canal, located in eastern Ontario, is a 202-km historic waterway connected by 23 operating lockstations that embodies this challenge. In collaboration with the federal managers of the waterway, Parks Canada, we used acoustic telemetry to determine if, when, and to what extent native and invasive fishes move throughout the system and the potential ecological and/or hydraulic factors influencing movements. We acoustically tagged two native fish species, largemouth bass (Micropterus salmoides; N=57) and northern pike (Esox lucius; N=114), and an invasive fish, common carp (Cyprinus carpio; N=54), and monitored movements for three years across a 60-km representative reach via 72 acoustic receivers. Our focus was on lock connectivity given this is the most likely pathway by which fishes move throughout the system, as most dam heights impede upstream movement.
Our results suggest lockstations in the Rideau Canal minimize, but not entirely restrict, connectivity. We documented 31 passage events by 21 tagged fish (9%) at six lockstations during our study. Potamodromous northern pike were responsible for 74% of passage events, with the remaining 26% conducted by largemouth bass. No common carp passages were detected; movements indicated carp favoured high-flow areas downstream of dams, regions with no pathway upstream. Most passages (60%) occurred in spring, corresponding with increasing temperatures and spawning seasons. Approximately 71% of passages occurred in the downstream direction, suggesting hydraulic factors may be entraining fish. Interestingly, only seven passages were recorded in 2020 – the year of reduced human mobility due to COVID-19 restrictions – implying effects of the “anthropause” on connectivity. Our work provides the evidence necessary to develop a strategy that carefully considers barrier management from both a native and invasive species perspective; our findings indicate lockstations appear to act as barrier to common carp dispersal, though they also confine native fishes. Given that anthropogenic waterways are globally pervasive, this research informs not only the conservation and management of the Rideau Canal, but also other waterways in Canada and beyond.