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

end of the exposure (time-to-effectAChE activity and time-to-recoveryAChE activity, respectively; Figure
2C). The apparent activity level was back-calculated to result in a relative concentration
(concentration/ AChE inhibition EC50) for each day of the growth period for each pulse. The
relative concentration for each day was summed across all the pulses to result in a total apparent
concentration for each day. The sigmoid slope used in the calculation of AChE activity using the
apparent concentration was the arithmetic mean of the sigmoid slopes for each pesticide present
on each day. The timecourse for relative prey abundance was modeled incorporating a one day
spike in prey drift relative to the toxicity and available prey base followed by a drop in
abundance due to the toxic impacts (Figure 3C). Recovery is assumed to be due to a constant
influx of invertebrates from connected habitats (aquatic and terrestrial) that are not exposed to
the pesticide. Incoming organisms are subject to toxicity if pesticides are still present and this
alters the rate of recovery during exposures. Incorporating dynamic effects and recovery
variables allows the model to simulate differences in the pharmacokinetics (e.g., the rates of
uptake from the environment and of detoxification) of various pesticides and simulate
differences in invertebrate community response and recovery rates (see below).
The relationship between final ration and somatic growth rate (Figure 4C) produces a
relationship representing somatic growth rate over time (Figure 4D), which is then used to model
individual growth rate and size over time. The growth models were run for 1,000 individual fish,
with initial weight selected from a normal distribution with a mean of 1.0 g and standard
deviation of 0.1 g. The size of 1.0 g was chosen to represent sub-yearling size in the spring prior
to the onset of pesticide application. For each iteration of the model (one day for the organismal
model), the somatic growth rate is calculated for each fish by selecting the parameter values from
normal distributions with specified means and standard deviations (Table 1). The weight for
each fish is then adjusted based on the calculated growth rate to generate a new weight for the
next iteration. The length (days) to run the growth portion of the model was selected to represent
the time from when the fish enter the linear portion of their growth trajectory in the mid to late
spring until they change their growth pattern in the fall due to reductions in temperature and
resources or until they migrate out of the system. The outputs of the organismal model that are
handed to the population models consist of mean weights (with standard deviations) after the
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