A demographic population model for American shad: Will access to additional spawning habitat upstream of dams increase population sizes?

American shad are in decline in their native range and modeling management scenarios could help guide restoration.  We developed a density-dependent, deterministic, stage-based matrix model to predict possible effects of transporting American shad to spawning habitat above dams on the Roanoke River.  We used data on sonic-tagged adults and oxytetracycline-marked young released above and below dams in the Roanoke River to estimate the initial population size and vital rates.  We used the model to predict stock size over 30 years under different scenarios of transport, egg production, and outmigration survival.  We also evaluated possible effects of increased survival for young or adults.  The model predicted a slow population increase over the next 30 years.  Transport was predicted to benefit the population only if high rates of egg production and young survival were achieved.  Presently, the estimated adult population (5,224 females) is much smaller than either of two assumed carrying capacity values for the lower Roanoke River.  Access to additional habitat would be most beneficial for populations nearing carrying capacity.  Better information about natural mortality and carrying capacity for American shad in regulated rivers would improve the model’s evaluation of the benefits of access to additional spawning habitat upstream of dams.