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

With the proposed action it is difficult to place an exact number on the percentage of a
population that is affected or how frequently a population is affected because of the lack of
information on and wide variability in the spatial and temporal uses of the registered
formulations containing carbaryl, carbofuran, and methomyl, compounded by the imperfect data
on where salmonids are at any given time. However, NMFS has sufficient information to make
reasonable inferences from the available use, exposure, and response data on the likelihood of
population-level consequences. Below we address whether the remaining fitness level
consequences identified from the risk hypotheses affect the viability of salmonid populations.
As mentioned earlier, we focus on the potential for reduced population abundance and
productivity.
Impaired swimming and olfactory–mediated behaviors
All life stages of salmonids rely on their inherent ability to smell, to swim, and to navigate
through a variety of habitats over their life span and to ultimately spawn successfully in natal
waters and complete their life cycle. We have shown that exposure to carbaryl and carbofuran,
compared to effects concentrations necessary to impair swimming behaviors, appears sufficient
to do so in some environments, especially in rearing locations for the juveniles. Although no
data were available to evaluate the effect of methomyl on swimming behavior, we find it
reasonable to apply the conclusions drawn for carbaryl and carbofuran due to the chemicals
sharing a similar mechanism of toxic action. Specifically, we expect that salmonids with
impaired swimming behaviors from AChE inhibition will show reduced feeding, delayed or
interrupted migration, reduced survival, and reduced reproductive success. We conclude that
exposed populations are likely to have reduced abundance and productivity as a result of
impaired swimming.
Based on the information we reviewed for carbaryl, carbofuran, and methomyl on salmonid
olfaction, we find differences in expected responses. For carbaryl, we conclude that it is unlikely
to affect salmonid olfaction at estimated concentrations. For methomyl, we located no
information on its effects to fish olfaction, and given the variation in olfactory responses
measured from other AChE inhibitors (OPs and carbamates) it is uncertain whether methomyl
will affect olfaction. For carbofuran, definitive evidence shows that olfaction in fish is affected
at low μg/L concentrations.
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