Navigating a seascape: physiological and environmental motivations behind juvenile North Pacific albacore movement patterns

Characterization of an animal’s movement patterns and the motivations behind those movements can allow us to predict their response to changes in the environment or ecosystem. In my thesis, I use biotelemetry data and mechanistic models to investigate the movements of albacore tuna within the context of their thermal biology as they move through a dynamic and heterogeneous thermal environment. My results indicate that albacore have thermal habitat constraints dictated by their inability to maintain a functional body temperature in SST below 11 °C, and high behavioral and physiological costs at SST above 20 °C. I show that albacore migrations are longer and have more consistent phenology and direction when fish are migrating between habitats whose sea surface temperatures trend below 13ºC and above 20 ºC. Albacore time their migrations with annual changes in the temperatures of their origins and destinations. I also show that thermal fronts serve as a dual resource to albacore. I characterize the movement of four tunas as they utilize sub-mesoscale features associated with a thermal front. For two weeks, the tunas swam between the warmest and coldest available waters, making on average 50 trips across the front per day, with 85% of these occurring during daytime. The use of the warm side of the front resulted in an increase in body temperature, and the strength of the front was directly correlated with foraging success. This work provides the necessary parameters to model albacore movement and a mechanistic understanding of the limits to albacore distribution