Effect of size on lake trout survival after a single sea lamprey attack

When lake trout Salvelinus namaycush were subjected to a single attack by a sea lamprey Petromyzon marinus in laboratory tests in 1986, percentage mortality was significantly higher in small fish (64%; 469-557 mm; N = 67) than in medium (44%; 559-643 mm; N = 45) or large fish (43%; 660-799 mm; N = 47). Additional studies conducted in 1987 with 55 medium (559-650 mm) and 52 large (660-825 mm) lake trout confirmed that there was no difference in mortality between the two larger size-groups. Mortality declined in lake trout over 559 mm, but was still greater than 43%. This level of mortality and the sea lampreys' apparently active selection of larger fish indicated that, contrary to previously published opinions, large size in lake trout (up to ∼800 mm in length) might not allow better survival from single sea lamprey attacks.