Modeling Migratory Energetics of Connecticut River American Shad

This paper presents an individual-based modelling exercise, in which migratory American shad (Alosa sapidissima) ascend the Connecticut River, spawn, and return to the marine environment.  We use an integrative approach, incorporating data and assumptions of bioenergetics, reproductive biology, and behavior to improve our understanding of the effects of migratory delays and thermal alterations on distribution, spawning success, and survival.  The model is complex, incorporating 62 randomly varying covariates.  We quantify the uncertainty within and among these covariate’s effects, and explore both how the covariates are likely to affect performance over a range of likely values, and how the uncertainty underlying them influences their predicted effects.  Individual and reproductive behavior, physiology, and energetics strongly affected both the distribution of spawning effort and the likelihood of survival to the marine environment.  Delays at dams (to both up- and downstream migrations) had dramatic effects on spawning success, driving a) total fecundity and its variance; and b) spatial extent of spawning.  Delays, combined with downstream triggers also determined the likelihood of survival to the marine environment.  In the absence of migratory delays, migratory distance had little effect on survival, but it did strongly influence both total fecundity and the spatial distribution of spawning effort.  In the presence of delays, spawning was largely restricted to the immediate vicinity of dams; in the absence of delays, spawning was distributed along the migratory corridor and throughout the available habitat, with most spawning occurring in the most upstream reaches.  Warming the river caused reductions in migratory distance and survival.  More research is needed on reproductive biology, behavior, and energetics to adequately understand the interplay of migratory delays and thermal alterations on shad populations; nevertheless, this exercise suggests that warming rivers through thermal discharge and climate change, and creating obstacles to migration in either direction can have significant detrimental effects to populations of American shad.