Determination of the seasonality effect on sea lamprey and TFM efficacy - Year One

Controlling larval sea lamprey (Petromyzon marinus) in Great Lakes tributaries with of 4-Nitro-3-(trifluoromethyl)phenol (TFM, a lampricide) is essential to reducing the number of spawning-phase sea lamprey, an invasive species capable of collapsing Great Lakes fisheries. An important component of treating streams with lampricide is ensuring that the proper amount of TFM is applied, effectively controlling sea lamprey populations while minimizing effects on non-target species. In this study, the Trout, Ocqueoc and Sucker Rivers, were selected to complete replicated stream-side bioassays in May, July, and September 2021 to determine seasonal changes in sensitivity to TFM. Larvae were collected and bioassays were conducted stream side. Larvae (gt 60 mm) were exposed to TFM for 12 hours in parallel diluters using stream water. A suite of water chemistries and larval condition parameters were collected during these tests and used to model seasonal changes in lampricide sensitivity differences. Seasonal changes in larval sea lamprey lampricide sensitivity were observed, with observations 11-27% lower in May and 43-73% higher in the early September than estimated by the prediction chart currently used by sea lamprey control agents. Stream water temperature and larval glycogen reserves appear to be the primary drivers of seasonal sensitivity differences. This research aids fishery managers to sustain fisheries by providing fishery managers with a tool to aid in more efficient TFM treatments and potentially less impactful sea lamprey control treatments.