Evaluation of Alternative Models of the Coastal Migration of Adult Fraser River Sockeye Salmon (Oncorhynchus nerka)
A set of stochastic discrete step models of individual fish movement was developed to investigate the efficiency of compass orientation as a migratory mechanism in the coastal homeward migration of Fraser River sockeye salmon (Oncorhynchus nerka). Ultrasonic tracking data provided empirical values for the required parameters. Alternative movement models were validated by comparing the results of Monte Carlo simulations and known features of sockeye migration: general aspect of individual trajectories, timing, success in reaching the goal, and spatial occurrence. The effect of different headings and directional precisions on the probability of success in reaching the goal were considered. The more complex models captured the essence of observed movement patterns, but the number of fish getting to the goal was lower than expected. Many "modeled" fish were lost in the complex web of channels and inlets characteristic of this area. We conclude that the preference of a compass direction is not a sufficient mechanism to explain the observed migratory behavior of Fraser River sockeye salmon in coastal areas. Other mechanisms, such as negative kinetic responses to water from nonnatal rivers or short-term learning, may prevent the fish from being trapped in complex areas.