Cooperative Fish and Wildlife Research Units Program: Mississippi
Education, Research and Technical Assistance for Managing Our Natural Resources

We measured initial mortality (fish judged non-releasable at weigh-in), pre-release mortality (fish judged non-releasable 1-2 h after weigh-in, includes initial mortality), and post-release mortality (fish that died during 5-day retention in net pens) in 14 live-release walleye Sander vitreum tournaments 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%, pre-release mortality was 3-54%, post-release mortality was 0-100%, and reference fish (walleye ≥ 31 cm captured by electrofishing and held in net pens with tournament-caught walleye to measure post-release mortality) mortality was 0-97%. Mortality was generally low in events conducted when water temperatures were below 14oC, but mortality was substantially higher in events when water temperatures were above 18oC. Mortality of reference fish suggests that capture by electrofishing and minimal handling when water temperature exceeds 19oC results in high mortality of walleye and that the mortality is largely a 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 per boat weighed in. Mortality was positively related to the depth at which walleye were caught and live well temperature and negatively related to live well dissolved oxygen concentration. Surface water temperature was the best predictor of mortality, and models were developed to predict the probability of ≤ 10%, ≤ 20%, and ≤ 30% pre-release and post-release mortality of tournament-caught walleye from water temperature.