Low thiamine levels in lake trout eggs is a condition thought to contribute to widespread recruitment failure in Great Lakes lake trout populations. Substantial, natural reproduction has not been achieved by lake trout in the Great Lakes, except Lake Superior, for decades despite continued stocking efforts. Low thiamine levels cause death or abnormal behavior in larval, juvenile and adult lake trout. This condition, known as thiamine deficiency or TD, has been associated with adult lake trout's dietary uptake of the thiaminase enzyme, which is present in prey species at different concentrations. Dose-response curves have been developed to predict mortality based on egg thiamine concentration. These curves may underestimate the response of lake trout to low thiamine because they do not consider sub-lethal effects. To investigate the sub-lethal effects of TD, I developed an individual based model (IBM) for larval lake trout. The IBM simulates the daily activities of fish that make it to the free swimming larval stage and tracks their growth and survival until they become thiamine replete. Low thiamine affects larval traits like prey capture ability and growth rate, which can be easily adjusted in the model. Simulation results indicate TD in combination with moderate predation or high predation alone can reduce survival to zero. Simulation results indicate lake trout maybe more sensitive to low thiamine than previously reported. The technique of using an IBM to develop a more accurate dose-response curve for wild populations is a new and promising way to evaluate the effect of stressors at the population level.
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