Lampricide residues in sea lamprey larvae carcasses recovered after 3-trifluoromethyl-4- nitrophenol (TFM) or TFM/Bayluscide stream treatments

Lampricide concentrations in whole larval sea lamprey (Petromyzon marinus) carcasses collected after lampricide treatments were determined to support risk assessment for non-target organisms that may consume lampricide-laden carcasses. Dead larvae were collected by Sea Lamprey Control personnel following the Ford River (Delta County, Michigan) 4.1 mg·L^-1 3-trifluoromethyl-4-nitrophenol (TFM) treatment, Sturgeon River (Baraga County, Michigan) 0.64 mg·L^-1 /7.1 µg·L^-1 TFM/niclosamide treatment, and two treatments on the Chippewa River (Isabella County, Michigan). The upper reach of the Chippewa River was treated with 3.1 mg·L^-1 /33 µg·L^-1 TFM/Bayluscide and the lower reach was treated with 4.1 mg·L^-1 TFM. Carcasses were removed from each stream via scap nets immediately after treatment completion. To assess instream degradation, half of the collected carcasses from both Chippewa River treatments were placed in cages and returned to the river for 2 days before they were analyzed for lampricide residues. The estimated mean and standard error of the mean (SEM) TFM concentration in the fresh carcasses (n = 80) collected from all the TFM and TFM/Bayluscide treated rivers was 4.6 µg·g^-1 (SEM =1.1 µg·g^-1 ). The mean concentration of niclosamide (the active ingredient in Bayluscide) in the fresh carcasses (n = 40) from the two rivers treated with TFM/ Bayluscide was 0.49 µg·g^-1 (SEM = 0.21 µg·g^-1 ). The mean 2-day postmortem carcasses from the Chippewa River TFM/Bayluscide treatment contained 0.14 µg·g^-1 (3%) of the TFM and 0.41 µg·g^-1 (64%) of the niclosamide found in the fresh-carcass group (4.4 µg·g^-1 TFM and 0.64 µg·g^-1 niclosamide). The mean 2-day postmortem carcasses from the Chippewa River TFM treatment contained 0.72 µg·g^-1 (12%) compared to the 6.1 µg·g^-1 of TFM found in the fresh-carcass group.