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

species-appropriate growth period (Table 2). A sensitivity analysis was run to determine the
influence of the parameter values on the output of the growth model.
The parameter values defining control conditions that are constant for all the modeled species are
listed in Table 1. Model parameters such as the length of the growth period and control daily
growth rate that are species specific are listed in Table 2. Each exposure scenario was defined by
a concentration and exposure time for each pesticide. The duration of time until full effect for
the pesticides was assumed to be within a few days (Ferrari et al. 2004), with a half-life of 0.5
days.
For prey, it is assumed there is a constant, independent influx of prey from upstream habitats that
will eventually (depending on the rate selected) return prey abundance to 1. As mentioned
above, however, these invertebrates are subject to exposure once added to the system, and
therefore prey recovery rate is a product of the influx rate as well as the exposure scenario.
While recovery rates reported in the literature vary, it is assumed a 1% recovery rate is
ecologically realistic (Ward et al. 1995, Van den Brink et al. 1996, Colville et al. 2008). It was
also assumed that regardless of the exposure scenario, relative prey abundance would not drop
below a specific floor (Figure 3B). This assumption depends on a minimal yet constant
terrestrial subsidy of prey and/or an aquatic community with tolerant individuals that would be
available as prey, regardless of pesticide exposure and in addition to the constant recovery rate.
No studies specify floors per se, but studies quantifying invertebrate densities following highly
toxic exposures indicate a floor of 0.2 is ecologically realistic (i.e., regardless of the exposure,
20% of a fish’s ration will be available daily; e.g., Cuffney et al. 1984). Finally, because prey
availability has been found to increase dramatically albeit briefly following pesticide exposures
(due to immediate mortality and/or emigration of benthic prey into the water column; Davies and
Cook 1993, Schulz 2004), a one-day prey spike is included for the day following an exposure.
The relative magnitude of the spike is calculated as the product of the standing prey availability
the day prior to exposure (minus the floor), the toxicity of the exposure, and a constant of 20.
This calculation therefore accounts for the potential prey that are available and the severity of the
exposure. The spike will be greater when more prey are available and/or the toxicity of the
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