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

carbofuran applications could cause population-level effects through acute mortality of juveniles,
particularly in areas of intensive agriculture and large urban or residential areas. We also expect
acute mortalities of juveniles from applications of carbaryl to forests and from exposure to 24(c)
carbaryl applications in estuaries in Washington State. However, we do not know how many
individuals are exposed each year due to these uses.
Sublethal effects caused by AChE inhibition, such as impaired swimming and olfactorymediated
behaviors, are also expected to result in adverse population-level effects. Swimming is
a critical function for salmonids. Individuals with impaired swimming ability will show reduced
feeding, delayed or interrupted migration, reduced survival, and reduced reproductive success.
We expect that carbaryl, carbofuran, and methomyl will occur at concentrations high enough to
impair swimming ability in occupied shallow water habitats. These effects may lead to
population-level consequences that hinder the survival and recovery of listed species.
Olfactory-mediated behaviors are also vital for salmonid survival. These behaviors include
detecting and avoiding predators, recognizing kin, locating natal waters for spawning, and
reproduction. Juvenile salmonids with impaired olfactory-mediated behaviors can lose their
ability to imprint on natal streams and avoid predators. Spawning is triggered by olfactorymediated
cues given and received by both sexes. If olfaction is inhibited, salmon may not
recognize these cues, resulting in reduced reproduction. The available information suggests that
carbaryl does not inhibit olfaction. Therefore, we do not expect to see effects to olfactory
mediated behaviors from carbaryl exposure. Currently there is not enough information to
determine the effect of methomyl on olfaction. However, exposure to carbofuran at low μg/L
concentrations will likely result in the impairment of olfactory-mediated behaviors. That in turn
will lead to increased predation and ultimately reduced juvenile and adult survivorship. As
pesticide exposure increases we expect to see more pronounced effects due to additive and
synergistic effects.
We also expect indirect effects from the a.i.s through reduced salmonid prey abundance and
subsequent reduced juvenile growth and probability of survival. Feeding during the period
immediately following emergence is vital for the survival of all ESA-listed Pacific salmonid fry.
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