If a migrant passes within the capture radius of a predator, it dies. Migrants obtain the river velocity from the hydraulic model node that is closest to their location. The random swimming component of migrant velocity is user-determined and has a constant magnitude. The frequency with which migrants change the random direction of their swimming velocity is independent of the movement time step. The user specifies the number of seconds that pass before a migrant chooses a new random swimming direction.
Predation is a three-dimensional phenomenon.
Each migrant and predator has a depth, and a migrant must be within a predator's capture radius over all three dimensions to be killed. The locations of nodes, migrants, and predators are tracked at a one-meter resolution. The model user can watch the fish as they travel downstream. We keep track of how many migrants die vs. survive their trip through the reach, and each migrant's travel time and path distance. The model is coded using the Swarm simulation system.