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

dominated by agricultural or urban land uses, healthy upstream or nearby habitats may be limited
and consequently, recolonization by salmonid prey is likely reduced (Liess and Von der Ohe
2005; Schriever, Ball et al. 2007). Additionally, many large, high-quality prey take a year or
more to develop (Merritt and Cummins 1995) indicating that recovery of biomass (as compared
to prey density) is likely a limiting factor (Cuffney 1984). Recovery to pre-disturbance levels is
unlikely in aquatic habitats where invertebrate abundances are repeatedly reduced by stressors.
We consider a 1% (control prey abundance per day) recovery rate as ecologically realistic to
represent recolonization by invertebrates in salmonid habitats (Ward, Arthington et al. 1995; Van
den Brink, van Wijngaarden et al. 1996; Colville, Jones et al. 2008).
Growth model results
Exposure to single insecticides for 4­, 21­ , and 60 day exposure durations
Population model outputs for the four salmon populations are summarized as dose-response
curves in Figures 44-47. As expected, greater reductions in population growth resulted from
longer exposures to the insecticides. The primary factor driving the magnitude of change in
lambda was the Prey Abundance parameter for each insecticide i.e., the 10th percentile survival
EC50 for salmonid prey. The AChE parameter for each of the insecticides was a secondary
factor compared to Prey Abundance. This is largely because the salmonid EC50s for AChE were
much higher, typically by an order of magnitude, than the prey survival EC50s.
Similar trends in effects were seen for each pesticide across all four life history strategies
modeled. This is apparent by the similar shape of the dose-response curves across species. The
curves plateau when there is no more reduction possible in the aquatic community i.e., the 20%
biomass of the aquatic invertebrate community is reached. Once that plateau is achieved, further
reductions in lambda are minimal with increasing concentrations. Clearly, the most toxic of the
pesticides affected salmon populations at lower concentrations, as is observed with carbaryl and
carbofuran where concentrations in the low μg/L range are sufficient to reduce populations’
growth rates compared to methomyl where 20 μg/L or greater are needed to reduce lambdas.
One factor that contributed to the similar responses observed was the use of the same surrogate
toxicity values for all four life history strategies. The stream-type Chinook salmon (Figure 45)
and sockeye salmon (Figure 46) models produced very similar results as measured as the final
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