Sea turtles migrate because of 3 reasons: Food, Reproduction, and Acclimatization, which are pretty common for migratory species. The means in which turtles arrive to their destinations is through sea currents, and they use earth's magnetic field and water chemistry to navigate.
So, to understand the migratory features of a particular sea turtle species, I would ask the following:
* Location of it's nesting grounds
* Location of it's foraging grounds
* Sea Surface Temperature (SST) of it's distribution area throughout the year
* Description of Oceanic Dynamics on it's distribution area, specifically Sea Currents and Upwelling.
* Salinity changes along it's distribution area, as well as any other chemical indicator of change in the water.