Development of an Individual Based Larval Model (ILAM) for Riverine Ecosystems I: Determination of Movement Patterns in a Racetrack Flume and Model Development

Larval dispersal of riverine ecosystems is strongly related to water movement. Currently, numerical models are able to generate flow fields and trajectories of passive particles, which are assumed to represent larval transport. A laboratory study was conducted in a racetrack laboratory flume which contained a shoreline along the inner boundary. This contribution summarizes the identification of larval behavioural aspects and the development of a correlated and biased individual based model (ILAM) for riverine larvae, representing movement patterns. Nase Carp (Chondrostoma nasus), a characteristic riverine fish species, was used as target species. Individual larval trajectories and larval orientation were monitored continuously. Upstream and downstream movement patterns were classified using a new method. As result, a solely passive representation of larval transport was found to be insufficient for riverine ecosystems. Moreover, with increasing flow passive movement of larvae dominated while active movement processes shifted to the shoreline. Based on these assumptions, the ILAM model was developed. This model distinguishes between several movement patterns. Embodied swimming speed and swimming directions depend on previously encountered probability density functions, representing randomness of individual behaviour. The model was validated successfully within a further study (part II: Model implementation and validation in a racetrack flume).