In this, the 2nd part of a study of Thunnus alalunga in the north-east Atlantic, populations and migrations are considered. The term 'population' is defined. The utilization of H. fusca as a biological 'marker' is considered and tagging experiments are described. Modal classes are examined: summary analysis, detailed analysis of fisheries. Internal temps and regulation are studied. The types of watering are defined and described and a statistical analysis as a function of the watering is made. An attempt at synthesis is made: Azorian, standard. Migratory determinism is examined.