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

at several times during an experiment. The test fish are usually fed twice daily, ad libitum, i.e.,
an over abundance of food is available to the fish. Therefore, any reductions in size are a result
of fish being affected to such an extent that they are not feeding even when presented with an
abundance of food. Subtle changes in feeding behaviors or availability of food would not be
detected from these types of experiments. If growth is affected in these experiments, it is highly
probable that growth of fish in natural aquatic systems would be severely affected. If effects to
growth are likely, we assess salmonid population-level consequences based on reductions in
juvenile growth and subsequent reduction in size prior to ocean entry.
Reproduction, at the scale of an individual, can be measured by the number of offspring per
female (fecundity), and at the scale of a population by measuring the number of offspring per
females in a population over multiple generations. The BEs summarized reproductive endpoints
at the individual scale from chronic freshwater fish experiments where hatchability and juvenile
and larval survival are measured. NMFS considers many other assessment measures of
reproduction, including egg size, spawning success, sperm and egg viability, gonadal
development, reproductive behaviors, and hormone levels. These endpoints are not generally
measured in standardized toxicity assays used in pesticide registration.
Sometimes qualitative observations of sublethal effects are summarized from 96 h lethality doseresponse
bioassays in EPA’s risk assessments. These observations generally were limited in the
BEs for carabaryl, carbofuran, and methomyl, and when noted, pertained to unusual swimming
behaviors. None of these behaviors were rigorously measured and therefore are of limited value
in assessing the effects of the three insecticides on Pacific salmonids. We do, however note a
few of the observations when they pertained to a relevant assessment endpoint, such as impaired
swimming. Some BEs presented toxicity information on degradates, metabolites, and
formulations. However, toxicity information on other or “inert” ingredients found in pesticide
formulations was usually not presented.
Results from multiple species tests, called microcosm and mesocosm studies, were also
discussed in the BEs to a varying degree. These types of experiments are likely closer
approximations of potential ecosystem-level responses such as interactions among species
(predator-prey dynamics), recovery of species, and indirect effects to fish. However, the
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