A mark-recapture experiment was conducted applying a two-sample stratified technique to estimate the number of Atlantic salmon smolts, Salmo salar, migrating out of the Conne River, Newfoundland. We developed a model where parameters are introduced to describe the mean time for the salmon to migrate between the release site and recapture site and to describe the probability of capture on a particular date. The latter are then used to expand the number of untagged smolts captured to estimate the daily run sizes. We discuss the advantages of this new approach over other models. For example, this formulation allows great flexibility in the experimental design, is robust to violations of assumptions, and allows the influence of environmental factors upon the parameters to be investigated.