Seasonal Variation in Sensitivity to the Pesticide Used to Control Invasive Sea Lamprey (Petromyzon marinus) Populations in the Great Lakes

Invasive sea lampreys continue to plague Great Lakes fisheries. To control this nuisance species, streams containing larval sea lampreys are treated with the pesticide 3-trifluoromethyl-4-nitrophenol (TFM) every 2-4 years. However, TFM application takes place from spring to fall, suggesting that variation in the sensitivity of larval lampreys to TFM could affect treatment effectiveness. To explore this question, larval sea lampreys were captured by pulsed-DC electrofishing in May, June, August, and October, and the TFM LC₅₀ was determined each time. The TFM LC₅₀ in May was 1.2 mg L^-1, increasing 2-3 times in June and August, and then decreasing by 48% in October. To ascertain if these differences could be explained by changes in the lampreys’ capacity to detoxify TFM, internal TFM concentrations and its metabolite, TFM-glucuronide, were determined using HPLC. Internal TFM did not vary seasonally, averaging 25-35 nmol g^-1 wet weight, and TFM-glucuronide was undetectable. We conclude that other factors such as differences in internal energy stores, temperature, body size and/or TFM uptake rates explain seasonal variation to TFM. Thus, if chemical control methods are being considered as a method of invasive species control, variations in the sensitivity of the target organism to the pesticide should be considered.