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ACUTE TOXICITY OF THE LAMPRICIDE 3-TRIFLUOROMETHYL-4-NITROPHENOL (TFM) TO SEVERAL SIZE RANGES OF LARVAL SEA LAMPREYS (PETROMYZON MARINUS)
Michael A. Boogaard1, Terrance D. Hubert1, and Jean V. Adams2
1U.S. Geological Survey, Upper Midwest Environmental Sciences Center, 2630 Fanta Reed Road. La Crosse, Wisconsin 54603
2U.S. Geological Survey, Great Lakes Science Center, 1451 Green Road, Ann Arbor, MI 48105
It has been speculated that the decrease in 3-trifluoromethyl-4-nitrophenol (TFM) application rates from the implementation of the sea lamprey pH/alkalinity minimum lethal prediction model in 1993 may have resulted in an increase in residual larval sea lampreys surviving treatment, in particular, larger larvae that are transformed or nearing transformation into the parasitic stage. In an effort to investigate this hypothesis, we conducted a series of toxicological exposures with TFM to several size ranges of larval sea lampreys including transformed larvae to determine the relationship of larval sea lamprey size and TFM sensitivity. The specific objective of this study was to compare the acute toxicity of TFM to several size ranges of larval sea lampreys including transformed larvae. Exposures (12 h) were conducted on five size ranges of larval sea lampreys (1, 29-59 mm; 2, 60-89 mm; 3, 90-119 mm; 4, 120-203 mm; and 5, transformed larvae) in 1999, 2000, and 2008. Results indicate a correlation between lamprey size and TFM sensitivity. Transformed larvae in two of the three years tested (1999 and 2008) and size range 4 larvae in one of the years tested (1999) required a higher MLC (minimum lethal concentration required to kill 99.9%) than size range 1, 2, and 3 larvae, ranging from 1.14 to 1.19 times the pH/alkalinity predicted sea lamprey MLC. Based on these results we recommend scheduling lampricide treatments when the stream is dominated by size range 1, 2, and 3 larvae. If larger larvae and transformed larvae are present, treatment managers should consider increasing target treatment concentrations a minimum of 20% to ensure effective control.