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
Schramm, Harold, L. Jr.; Vondracek, Bruce; French, William, E.; Gerard, Patrick, D..
Factors Associated with Mortality of Walleyes and Saugers Caught in Live-Release Tournaments.
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