Migratory and territorial are hardly exclusive. Many animals maintain a breeding territory, then migrate and establish a winter territory. They may even defend ephemeral territories along the way. However, dolphins are highly social and not at all territorial. Most nearshore dolphin sightings are of the Bottle-nosed Dolphin. This species spends a lot of time on the surface just outside the breakers, feeding opportunistically but also doing a fair bit of "just hanging out," as you put it. It does not migrate to any significant degree.