Pedant mode on /
They should more properly be called 'common bottlenose dolphins' (Tursiops truncatus) to distinguish them from the indo-pacific bottlenosed (T. aduncus), which has been DNA'd to 'prove' separate species. They used to be considered one species.
The Indo-pacific is not found in the Atlantic.
There is an ongoing debate about whether or not the Common should be further divided into inshore and tropical offshore. I know work is going on gathering harpoon samples for DNA, but do not know the results or whether there is a consensus.
My daughter, who knows a thing or two about Dolphins but is no longer doing active research, feels they are separate species because of localized feeding patterns and the fact the inshore variety are not found deep.
Splitters and lumpers - bit like birds really