Stayers, Movers and Commuters: A PIT-Telemetry Study of Salmonid Movements in a Small Tributary of the Sainte-Marguerite River

In this study, we used a combination of stationary and portable passive integrated transponder (PIT) antenna systems to investigate the summer and fall spatial behavior of tagged individuals of juvenile Atlantic salmon (Salmo salar) and brook trout (Salvelinus fontinalis) of the Xavier brook, a small tributary of the Sainte-Marguerite River (SMR) (Québec, Canada). 200 fish (168 salmon parr and 32 trout) were tagged using half-duplex 23-mm PIT tags and monitored from August to November 2007. Stationary flat-bed antennas spanning the width of the channel were installed at the downstream end, center and upstream end of the 2,5 km-long study section. These three stationary PIT systems provided continuous remote monitoring of the movement of PIT-tagged fish over the antennas. Every two weeks, a 2.5 m-long portable PIT antenna was used to scan the entire study section, thereby providing the exact location of tagged fish. Analysis of this data set revealed three different groups of spatial behaviour. Apart from the well documented groups of «stayer» and «mobile» fish, we identified a new group of fish that we named «commuter» fish. These fish, which represented 16% of the fish in the study, entered the tributary at sunrise, often in small groups of 2-3 tagged individuals. They then travelled in the upstream direction, frequently passed our most upstream stationary antennas, and then returned to the main stem of the river before sunset. To the best of our knowledge, this type of exploratory behavior has never been described before in the literature and it could have not been detected without the several stationary PIT systems used in this study. These results are used to discuss the potential contribution of PIT-telemetry to the development of the understanding of how fish exploit the mosaic of habitats and resources available within the riverscape.