Monitoring fish behaviour in a gas supersaturated river

This experiment will be conducted to investigate how wild, river-resident fish respond to levels of gas supersaturation. Several studies have focused on migratory salmonids but there is little information on how fish that spend their lives in a river exposed to gas supersaturation may be affected by the presence of total dissolved gas supersaturation. Wild brown trout will be captured from the river and held in net pens for up to four weeks. Wild landlocked Atlantic salmon (bleke) will be captured downriver of the dam and transferred upriver to the site to be paired with the trout in nets. Four nets (4x4x5m) will be used to keep up to 12 brown trout and salmon per replicate (N=8 replicates). Replicates will occur in each season over two years: September, December, March, and June for representative differences in gas supersaturation and temperature over time. The total number for this experiment will therefore be 384 wild trout or salmon. Each fish in the holding study will be tagged with archival tags and released into the caged net pen for up to four weeks and then killed. One hundred additional brown trout will be tagged with acoustic transmitters and released into the river to be detected within an array of acoustic receivers for at least one year. The expected distress will be moderate but all fish will be anaesthetized during procedures to minimize distress. Gas supersaturation is often an overlooked consequence of river regulation but the responses of animals must be understood and accounted for in order to responsibly manage rivers. We cannot replace observations of wild fish with simulations because we do not have the baseline understanding of behaviour with which to carry out a simulation, which is why we wish to conduct the project. We have selected a number of fish that we expect to yield reliable results without being an excessive number. By conducting both components of the experiment we consider this a refinement that accounts for potential uncertainty in the project.