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

Once fry have completely absorbed the yolk-sac, they are dependent on the local invertebrate
population and may starve if sufficient food is not available. As salmonid prey are sensitive to
the expected exposures to each of the insecticides, as well as from mixtures containing the three
a.i.s, we expect death and a variety of sublethal effects to salmonid prey. If the salmonid prey
base is limited while fry are in this life stage, juvenile growth will be significantly hindered.
Many of the invertebrate communities are already degraded due to poor habitat conditions and
poor water quality. These conditions make it more difficult for the prey base to recover
following an exposure event. Thus, juvenile survivorship will be low and may consequently lead
to a decrease in lambda for the affected population.
Based on the NMFS growth models, a four-day exposure to expected concentrations of carbaryl,
carbofuran, and methomyl will substantially reduce a population’s growth rate due to prey base
reduction. All four life history types modeled demonstrated this effect. As exposure duration
increases, we expect more pronounced effects on salmonid prey abundance and a longer prey
recovery period leading to further reduced salmonid growth and decreased survival.
We expect that all effects will be more pronounced in drainage basins that include high use
areas, i.e., major agricultural, urban, or residential centers. To determine which ESUs/DPSs will
be affected by the action, we compare the range of each species to the locations of high use land
classes. Species that occupy major agricultural basins, such as the Willamette basin or California
Central Valley, have a much higher risk of exposure than species found in uninhabited, nonagricultural
areas.
California Coastal Chinook Salmon
The CC Chinook salmon ESU consists of 10 historically functionally independent populations in
California from Humboldt County in the north to Sonoma County in the south. Historic annual
escapement was around 73,000 fish with most of these being produced in the Eel River. Today,
annual returns to the Eel River system is estimated at 150 to 2,800 fish. Runs in the Russian
River may be viable, though the short-term trend is negative. Lack of data precludes
development of population growth rates or trends for all other populations.
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