for context, look at the range of one of their food sources, the sardine: http://www.chefs-resources.com/files/Sardines-Sprat-Pilchards-Brisling/Sardine-range.j

for context, look at the range of one of their food sources, the sardine: http://www.chefs-resources.com/files/Sardines-Sprat-Pilchards-Brisling/Sardine-range.jpg http://www.chefs-resources.com/files/Sardines-Sprat-Pilchard... This greatly restricts their over-all range. To contrast dolphins, there are huge swaths of the land mass of the world with almost no human population, and we seem to gather in certain spots for certain reasons, most life does this, so it's not just a matter of the total volume of the ocean vs the entire population of dolphins.