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

Figure 47. Percent change in lambda for sockeye salmon following 4 d, 21 d, and 60 d exposures
to carbaryl, carbofuran, methomyl. Open symbols denote a percent change in lambda of less than
one standard deviation from control population. Closed symbols represent a percent change in
lambda of more than one standard deviation from control population.
By applying some of these changes in lambda to known threatened and endangered populations’
lambdas from Appendix 2, significant reductions in population viabilities are anticipated. For
example, if the Puget Sound Chinook salmon Green River population with a lambda of 0.67 is
exposed to carbaryl at 10.0 μg/L for 4 d, a concentration attainable in off-channel habitats, we
would expect a reduction in lambda by 11% (Table 74) or 8% (Table 75) depending whether the
individuals exhibit ocean-type or stream-type life histories. These reductions would be severe to
the population and are primarily a result of reductions in juvenile growth from impacts to
salmonid prey. Even for those lambdas that are well above one such as Central Valley Chinook
salmon Spring Runs’ Butte Creek population (lambda = 1.3), reductions of 11% would have
major consequences to a population’s viability from reduced growth of juveniles. The
repercussions to these populations’ viabilities are increased with increasing concentrations,
durations, multiple applications, and when mixtures are incorporated.
Exposure to multiple applications of carbaryl or methomyl
We constructed two scenarios to evaluate the potential population effects from multiple
applications of carbaryl and methomyl (Table 80). We used concentrations from AgDrift model
outputs to estimate drift contributions of carbaryl into an off-channel habitat (Table 52).
Populations exposed to carbaryl drift within off-channel habitats following four applications
would experience severe declines in population growth rate ranging from 15-19%. Interestingly,
a single application would result in notable reductions in the four modeled population’s lambdas
as well, ranging from 8-11%. Similar to the carbaryl modeled scenario, methomyl applied to
sweet corn ten times (the label allows for 14 applications at 1 d intervals) resulted in significant
reductions in lambdas ranging from 6-8%. A single application did not result in a significant
reduction in lambda for any of the four populations.
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