Explanations for Seasonal Variability in the Sensitivity of Sea Lampreys to the Chemical 3-Trifluoromethyl-4-Nitrophenol (TFM), Used to Control Invasive Sea Lamprey in the Great Lakes

One of the greatest nuisance species in the Great Lakes is the sea lamprey (Petromyzon marinus), a parasitic jawless vertebrate which uses its oral disk to feed on the blood of host fishes. The chemical 3-trifluoromethyl-4-nitrophenol (TFM) is now widely used to control sea lamprey populations because it is selectively toxic to larval sea lampreys. However, larval sea lamprey TFM sensitivity varies seasonally, but the underlying causes are not understood. The present study determined the relative contributions that seasonal variations in energy stores and water temperature play in explaining these differences in TFM sensitivity. Accordingly, larval sea lampreys were collected in the spring, summer and fall and returned to the Hammond Bay Biological Station on Lake Huron, where they were held at the same temperature as their natal streams. Following toxicity tests, whole-body TFM concentrations and energy stores were quantified. We conclude that a combination of low glycogen stores and lower body mass explain the greater sensitivity of larval sea lampreys to TFM.  Thus, lower concentrations of TFM may be effective if applied in the spring, but higher doses may be needed later in the year, when the animals are larger and have greater energy stores.