Carbaryl, Carbofuran, and Methomyl - National Marine Fisheries ...

invertebrates exposed to elevated temperatures, so where elevated temperatures co-occur with
OPs and carbamates the effect to aquatic life is likely greater than at lower temperatures. Many
salmonid populations reside in watersheds which have been listed by the four western states as
impaired due to temperature exceedances. We therefore discuss qualitatively temperature
impacts on salmonids population responses to the stressors of the action.
J. Exposure to specific pH ranges can affect the toxicity of the stressors of the action.
Some data indicate acute toxicity of carbaryl and carbofuran increases as pH increased based on
the available freshwater fish assays (Mayer and Ellersieck 1986). Other data indicated that
toxicity was reduced in pH greater than 9 due to rapid hydrolysis i.e., a half-life of 30 minutes in
pond mesocosms. For methomyl, pH seems to have less of an influence on hydrolysis rates.
Within the Pacific Northwest and California pH varies seasonally and typically may range from
6 – >9. We expect that salmonids exposed to both pH ranges at or near physiological tolerance
limits and the three insecticides concurrently may die at relatively lower concentrations
compared to salmonids exposed in laboratory assays. We therefore discuss qualitatively pH
impacts on salmonids population responses to the stressors of the action.
Effects to Salmonid Populations from the Proposed Action
Here we translate individual fitness consequences to potential population-level effects using both
quantitative and qualitative methods. We quantitatively translate reduced survival of juveniles
based on four-day exposures to four populations of salmonids including ocean-type Chinook,
stream-type Chinook, coho, and sockeye salmon. We employ a life history population model
that incorporates changes in first-year juvenile survival rates and then translates them into
predicted changes in the modeled population’s intrinsic rate of growth, i.e., lambda (Appendix
1). We discuss the percent change in lambda in the context of expected concentrations of the
three insecticides in salmonid habitats. We focus on the concentrations at which a significant
departure occurs from the unexposed population and compare them to expected environmental
concentrations described in the Exposure Analysis. We also discuss in general terms the
likelihood of exposure to the range of pesticide concentrations that occur in salmonid habitats.
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