1.4. Design concepts

Following the ODD framework and terminology, we briefly present here some design concepts characterizing OSMOSE.

1.4.1. Basic principles

Dieta data, such as those of [Shannon et al., 2003], suggest that patterns in fish diets include variability in time and space and prey switching, cannibalism and omnivory. Therefore, two species can be a predator or prey of one another depending on the life stages considered. Therefore, predation in Osmose is size-based, taking into account thresholds for predator/prey size ratio, and relies on the spatio-temporal co-occurrence of individuals.

1.4.2. Emergence

From the local interactions, population and community dynamics emerge. In particular, the whole food web structure emerges from size-based local predation interactions.

1.4.3. Adaptation

Adaptation is not implemented in Osmose.

1.4.4. Objectives

Objectives are not implemented in Osmose.

1.4.5. Learning

Learning is not implemented in Osmose.

1.4.6. Prediction

1.4.7. Sensing

Schools are assumed to know perfectly all the potential prey which are located in its vicinity, i.e. in the same cell of the grid. They also know the limits of their habitat.

1.4.8. Interaction

Super-individuals/schools interact locally through predation events.

1.4.9. Stochasticity

There are different sources of stochasticity in the model. First, the order at which schools act and interact. There is a randomization of the precedence of schools crossed with a randomization of different sources of mortality (predation, fishing, other natural mortality). In addition, fish movements are also randomized within their habitats.

1.4.10. Collectives

As the total number of fish (from eggs to adult fish) to be taken into account in the simulated system can reach a value of the order of \(10^{12}\), the model was not brought down to the fish level but to an aggregated level consisting of a group of fish having similar ecological attributes. The unit of action and interaction, i.e., the “super-individual” as defined by [Scheffer et al., 1995], is a group of fish having the same size, the same spatial coordinates, requiring similar food, and belonging to the same species (therefore having similar physiological and morphological characteristics). For convenience, this super-individual is also called a “fish school” in the following sections.

1.4.11. Observation

For model testing and fitting, a variety of auxiliary state variables can be used in output of the model and compared with observations, data time series, and maps. Typically, species biomass and commercial catches, age or size distribution of abundance/biomass, diets can be confronted to observations.