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

pesticide products containing carbaryl, carbofuran, and methomyl are applied. We considered
several sources of information to define the range of potential exposure to action stressors. EPA
provided a number of exposure estimates with maximum concentrations of 153, 35, and 99 μg/L
predicted for registered uses of carbaryl, carbofuran, and methomyl, respectively. We generated
additional exposure estimates for shallow off-channel habitats with predicted concentrations
exceeding 1,000 μg/L for carbaryl and carbofuran, and a peak concentration of 58 μg/L for
methomyl. Additionally, we considered monitoring data presented by EPA and from other
sources which indicate comparable concentrations of carbaryl, carbofuran, and methomyl have
been detected in surface waters within the four states where the listed salmon and steelhead are
distributed (85, 32, and 175 μg/L, respectively).
We assume that the exposure estimates provided by EPA in the BEs and additional modeling and
monitoring information provided above represent realistic exposure levels for some individuals
of the listed species. Further, we assume the distribution within the range of exposures is a
function of pesticide use and the duration of time listed salmonids spend in these habitats. All
listed Pacific salmon and steelhead occupy habitats that could contain high concentrations of
these pesticides at one or more life stages. However, the time spent in these habitats varies
among species. Adult salmon and steelhead spend weeks to several months in freshwater
habitats during their migration and spawning activities. Immediately after emerging from the
gravel substrate and transitioning from alevins to fry, salmonids move to habitats where they can
swim freely and forage. At this point in their development most salmon occupy freshwater
habitats. Chum salmon are an exception. They immediately migrate downstream following
emergence to nearshore environments in estuaries near the mouth of their parent stream. Upon
arrival in the estuary the chum salmon fry inhabit nearshore areas at a preferred depth of 1.5-5 m.
In Puget Sound, WA, surveys indicate chum salmon fry are distributed extremely close to the
shoreline and concentrated in the top 6 inches of water. Therefore, chum salmon fry are less
likely to be exposed to high concentrations of pesticides than other salmonids given the duration
of time spent in shallow water habitats and the habitat they occupy. They may reside
immediately next to the shore in estuaries for as little as one or two weeks before moving
offshore or into deeper-water habitats within the nearshore environment. Sockeye salmon fry
most frequently distribute to shallow beach areas in the littoral zones of lakes. They initially
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