Here we emphasize on the main features of the model structure.IBASAM is fully described by Piou & Prévost(2012).
In the river phase, individuals grew in weight according to individual and stage-dependent growth capacity and influenced by water temperature, population density and river flow. Growth increments in weight were then allocated to fat reserves (Fat) or somatic growth through an increase in body length depending on a variable individual propensity to accumulate fat. Survival in the river was phase dependent, with higher mortality for maturing individuals and during winter. The triggering of sea migration was size dependent 6 months before the run. The smoltification process allows an individual that was in the river (‘parr’) to become physiologically ready to run into the sea (as ‘smolt’). The probability of smolting for an individual followed a reaction norm based on its body length (Buoro, Prévost & Gimenez 2010).
Once at sea, individuals grew in weight following a Gompertz function depending on specific individual characteristics and overall oceanic conditions. In this function, a NoiseSeat factor repre- sented a daily environmental condition for growth. In the absence of EC, NoiseSeat was simply a normal random number centred on MeanNoiseSea = 1 and of variance 0 1. With EC, MeanNoiseSea decreased through time and NoiseSeat was a normal random number with variance 0 1 but centred on the MeanNoiseSea of the year. Each replicate of simulations had consequently different environmental conditions. Fat and body length accumulation were allocated as in the river phase. Survival at sea was size dependent with a clear disadvantage for small individuals.