What is the population of dolphins today?
I don’t think you are going to get anything close to an accurate answer for this question. There are at least 40 species of dolphin and porpoise (there is some argument about whether some species are subspecies of another), and very little is known about most of these. Population estimates range from several million (and no more accurate than that) for some species such as the common dolphin, Delphinus delphis, to as few as 50 for the Yangtze river dolphin, Lipotes vexillifer. I think the only consistent thing is that all reports (google “global dolphin population”) point to a steady decrease in numbers.