When Dead Fish Keep Swimming: Short-Term Biotelemetry of Walleye and Sauger after Catch and Release

We studied the movements and fate of walleye (Sander vitreus) and sauger (S. canadensis) during the 7 days following release from competitive angling tournaments in Saskatchewan in 2015. For several events we used externally attached radio tags equipped with accelerometers (mortality sensors) to indicate if and when fish stopped moving. A number of fish triggered mortality sensors within the first 24-48 hours after release, but these “dead” fish subsequently made normal movements. Similarly, some fish with acoustic tags did not move for prolonged periods (suggesting mortality), and then either moved long distances and/or were re-captured by anglers. At one tournament mortality of tagged fish was as high as 60%, with the majority depredated by American white pelicans in the first 72 hours after release. Depredation may be an important factor affecting mortality after release in some freshwater systems, especially if debilitated fish spend time on the surface. In our studies accelerometers were not useful additions to tags for identifying mortality events over short time periods. We conclude that mortality may be difficult to recognize using short-term biotelemetry because of a variable period of dramatically reduced movement immediately following release.