Simulation of Dispersal of Sockeye Salmon (Oncorhynchus nerka) Underyearlings in Babine Lake

The movement of underyearling sockeye salmon (Oncorhynchus nerka) in Babine Lake was computer simulated using a grid array with reflection principles applied for the complex shoreline boundaries. Dispersal was in accord with bivariate density functions summed appropriately to give 25 discrete components, with the standard deviations related to observed swimming speeds. Directionally biased dispersal was simulated using the lognormal density function. Natural movement of sockeye underyearlings in Babine Lake suggests three seasonal periods: (1) May 25–June 12; (2) July 13–August 28; (3) August 29–October 12. For (1), natural movement is best simulated by assuming that 90% of the fish move with a 10:90 bias toward southward movement, while 10% of the fish move at random; for (2), the best assumptions are that 50% of the fish move with a 90:10 bias for northward movement and 50% move at random; for (3), the best simulation assumed that 100% of the fry move at random. Considering the simplicity of the model assumptions, the fit to the data for natural movements is good. To construct a better predictive model the directional bias mimicked by the lognormal density function should be divided into components related to physical circulation in the lake basin and components related to fry behavior. The architecture of the computer program is briefly described and could be applied to other salmon dispersal studies. Key words: sockeye salmon, simulation, natural movements, fry distribution