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

D. Impair swimming which leads to reduced growth (via reductions in feeding), delayed and
interrupted migration patterns, survival (via reduced predator avoidance), and reproduction
(reduced spawning success).
Swimming is a critical function for anadromous salmonids. The primary line of evidence for this
hypothesis is impaired swimming behaviors following exposure to carbaryl, carbofuran, and
methomyl. A secondary line of evidence for this hypothesis is studies showing swimming
behavior modification following exposure to other AChE-inhibiting chemicals such as the OPs,
as we anticipate the results are similar in nature. Several studies regarding the effects of carbaryl
on the swimming related behaviors were reviewed, with effects on predator avoidance,
schooling, and feeding behaviors occurring at carbaryl concentrations of ~100-1,000 µg/L in
laboratory studies (Weis and Weis 1974; Arunachalam, Jeyalakshmi et al. 1980; Little, Archeski
et al. 1990; Carlson, Bradbury et al. 1998; Labenia, Baldwin et al. 2007). Only one study was
available for carbofuran showing effects to social behaviors at 5 µg/L (Saglio, Trijasse et al.
1996), and no studies were located for methomyl. Concentrations at which effects were noted
for carbaryl and carbofuran are within the ranges of concentrations estimated by the various
modeling methods, especially for the off-channel habitat locations. We anticipate similar effects
will occur with methomyl because it has the same mechanism of action as carbaryl and
carbofuran, inhibition of AChE (which is correlated to swimming impacts). However, we expect
it will take greater concentrations of methomyl compared to carbaryl and carbofuran to affect
swimming. We expect that these levels are likely from concentrations resulting from aerial drift
into off-channel habitats. This is because concentrations of methomyl necessary for AChE
inhibition and acute lethality (LC50) are greater than carbaryl and carbofuran concentrations
necessary to inhibit AChE and kill fish. We also discussed compelling evidence that OPs impair
salmonid swimming behaviors and also show associated reductions in AChE activity.
The most sensitive swimming endpoints are those associated with swimming activity compared
to those that measure swimming capacity (Little and Finger 1990; Little, Archeski et al. 1990).
The ecological consequences to salmonids from aberrant swimming behaviors are implied
primarily through the impairment of feeding, translating to reduced growth. Impaired swimming
behavior correlated with both AChE inhibition and increased mortality from predation (Labenia,
Baldwin et al. 2007). Although NMFS was unable to locate results from field or laboratory
experiments for the other remaining endpoints of this hypothesis, we conclude that swimming
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