Comparison of Larval Sea Lamprey Life History Characteristics in a Lampricide‐Treated Tributary and Untreated Tributary System of Lake Champlain

Abstract

AbstractControl of sea lampreys Petromyzon marinus in Lake Champlain and the Laurentian Great Lakes is dependent primarily on selective lampricides that reduce the density of sea lamprey larvae in tributary streams. After lampricide treatment, recolonized larval sea lampreys may experience enhanced growth from density‐dependent factors, which may lead to transformation at a larger size and younger age than would have occurred before treatment. In this study, the effects of lampricide treatments on larval sea lamprey life history characteristics were compared between Lewis Creek (Vermont), a treated stream, at 4–5 years posttreatment and the untreated Pike River–Morpion Stream system (Quebec, Canada). Sea lamprey habitat was measured in each stream at approximately 100 randomly selected transects, and larval density was determined using a backpack electrofishing unit during 1999 and 2000. Larval sea lamprey density was approximately threefold higher in Lewis Creek than in the Pike River and Morpion Stream in both years. Growth measured in length and weight indicated that neither treatment nor low density created conditions for faster growth. During 1999, transformers were, on average, shorter and younger in Lewis Creek (131 mm; 100% age 4) than in the Pike River–Morpion Stream (143 mm; 100% age 5). During 2000, the majority (75%) of transformers were age 5 in all streams. Weights of age‐4 transformers in Lewis Creek (1999 and 2000) and the Pike River (2000) were higher than those of age‐4 ammocoetes in those streams. Our results suggest that the first year‐class to become reestablished after lampricide application may transform at a younger age and smaller size than fish of the same age‐class in an untreated stream. Treatment intervals must adapt to changes in age at transformation to prevent transformers from leaving Lake Champlain and Great Lakes tributaries.