Factors Associated with Mortality of Walleyes and Saugers Caught in Live-Release Tournaments

—We measured the initial mortality (fish judged nonreleasable at weigh-in), prerelease mortality (fish judged nonreleasable 1–2 h after weigh-in [which includes initial mortality]), and postrelease mortality (fish that died during a 5-d retention in net-pens) in 14 live-release tournaments for walleye Sander vitreus conducted in April–October 2006 and April–July 2007 in lakes and rivers in Michigan, Minnesota, North Dakota, South Dakota, and Wisconsin. Among the 14 events, initial mortality was 0–28%, prerelease mortality was 3–54%, and postrelease mortality was 0–100%; the mortality of reference fish (walleyes 31 cm long that were captured by electrofishing and held in net-pens with tournament-caught walleyes to measure postrelease mortality) was 0–97%. Mortality was generally low in events conducted when water temperatures were below 148C but substantially higher in events when water temperatures were above 188C. The mortality of reference fish suggests that capture by electrofishing and minimal handling when the water temperature exceeds 198C results in high mortality of walleyes that is largely the result of the thermal conditions immediately after capture. Mortality was not related to the size of the tournaments (number of boats), the total number or weight of walleyes weighed in, or the mean number or weight of walleyes weighed in per boat. Mortality was positively related to the depth at which walleyes were caught and the live-well temperature and negatively related to the live-well dissolved oxygen concentration. Surface water temperature was the best predictor of mortality, and models were developed to predict the probability of prerelease and postrelease mortality of 10, 20, and 30% or less of tournament-caught walleyes due to water temperature. Organized fishing tournaments began in North America in the 1960s and rapidly grew in number (Schramm et al. 1991; Schramm and Hunt 2007). The initial surge in tournaments was directed primarily at black bass Micropterus spp. Substantial growth in the size and number of black bass tournaments elicited concern among fishery managers and tournament organizations about high exploitation and depletion of fish. Live release was championed by several tournament organizations to reduce potential depletion of black bass populations and soon became standard procedure for bass tournaments. Concern about the effectiveness of live release (Schramm et al. 1991) stimulated numerous studies of mortality of tournament-caught black bass (reviewed in Wilde 1998; Edwards et al. 2004; Schramm et al. 2006) and development of several procedural guides to help anglers and tournament organizers achieve high survival of released bass (e.g., Gilliland and Schramm 2002; Tufts and Morlock 2004). Organized tournaments in which anglers fish for walleye Sander vitreus and sauger S. canadensis began in the late 1970s (Schramm et al. 1991). Trends in walleye tournaments have not been measured but, paralleling the expansion of inland fishing tournaments (Schramm and Hunt 2007), appear to have rapidly grown in number and participation. Most walleye tournaments were live-release events, and walleye * Corresponding author: [email protected] 1 Present address: Department of Wildlife and Fisheries, South Dakota State University, Brookings, South Dakota 57007, USA. Received January 13, 2009; accepted October 8, 2009 Published online January 14, 2010 238 North American Journal of Fisheries Management 30:238–253, 2010 Copyright by the American Fisheries Society 2010 DOI: 10.1577/M09-003.1 [Article]