UBC Theses and Dissertations
A modeling investigation of migratory behavior in fishes : a case study with sockeye salmon Huato Soberanis, Leonardo
This thesis is composed of two separate spatially-explicit state-space dynamic models developed with the general objective of contributing to the understanding of migratory behavior in fish. The first model focuses on the behavior of mature adults during their reproductive migration, while the second focuses on the migratory tactics of fish during their migration cycle. Both models were applied to the marine migration of sockeye salmon (Oncorhynchus nerka) from the Fraser River. The first model is based on the hypothesis that the migratory behavior of returning individuals arises as an adaptive response to minimize a measure of the total costs of migration, given an expectation of the state of the environment during the migration (defined in terms of currents, temperature, and risk of predation). The model predicts that the higher swimming speed observed when sockeye salmon reaches the coast, and the use of the Juan de Fuca as the primary route to reach the Fraser River, are likely a response to a higher risk of mortality in the coast. The model also indicates that given the short arrival time of individuals from the same race, they either start their migration from a short longitudinal range, or are distributed across a wider range and start their migration at different times, with individuals further away from the Fraser River starting earlier. Predicted swimming speed and orientation resulted very sensitive to the spatial distribution and value of predation risk. This model could not predict the oceanic migration route and the latitude of landfall of Fraser River sockeye. I concluded that the spatial distribution of mortality was not properly represented, or that the tradeoff used to define the model was not adequate. The second model is based on the hypothesis that juvenile fish have a tradeoff between foraging activity and migration activity. The model was able to predict the following characteristics for sockeye salmon from the Fraser River: 1) Juveniles migrate along the coast and then move into the Alaska Gyre where they stay the rest of their oceanic residence. Model predictions do not support the commonly held hypothesis of an annual circuit around the Alaska Gyre. 2) The juvenile migration arises as a response to high zooplankton density in the coast at the time of the migration, although the high risk of mortality there creates a bottleneck in their life cycle. 3) The model predicts a seasonal growth pattern as a response to the seasonality of zooplankton density. 4) Juvenile fish display higher swimming migration activity than adults. 5) Individuals behaving optimally distribute below the observed thermal limits, however their distribution follows that of prey density. 6) The size-dependency of mortality observed during the smolt-to-adult phase likely arises from smaller individuals taking longer to swim through the coast.
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