The common dolphin (Delphinus delphis) is the most abundant cetacean in the world, with a global population of about six million.

The long-beaked common dolphin was thought to have a disjointed range in coastal areas in tropical and warmer temperate oceans.

Therefore, long-beaked and short-beaked common dolphins are now listed as the same species under the scientific name of Delphinus delphis.

[11][12][13] Currently, the common dolphin is divided into four subspecies:[11][14] Many extinct cetacean species were once lumped into Delphinus, but have since been placed in other genera.

[16] Another species known as Delphinus brevidens was reassigned to the genus Stereodelphis which is now generally considered synonymous with Squalodon.

In the Northwest Atlantic, they can be found from Cape Hatteras North Carolina, to Newfoundland and are strongly associated with the Gulf Stream.

Dolphins in this region can often be found in areas that have certain geological factors like underwater canyons and ridges because this is where up-welling occurs which result in greater nutrients.

Short-beaked common dolphins can also be found in Europe, particularly the Scotian shelf, the Black Sea and the Mediterranean.

That being said, closely related individuals are usually found in similar geographical locations fairly consistently, providing evidence that this species displays site fidelity (at least in the Northeastern Atlantic).

Male common dolphins display greater site fidelity in relation to their kin than females.

These whistles are believed to serve as an acoustic label, and provide identification information similar to that of a name.

It takes approximately 1 year for a calf to learn its signature whistle after which it remains stable for the rest of a dolphin's life.

These interactions take place in the deepest part of the Gulf, furthest from shore, and usually consist of a total of about 60 dolphins from all three species.

There is one confirmed case of a hybrid between a bottlenose and common dolphin in southern Spain, an important feeding ground for both species.

Moderate levels of metal pollutants, which are thought to negatively impact dolphin health,[35] have been measured in some populations.

About 1000 short-beaked common dolphins are bycaught in the North Atlantic each year by either tuna drift, trawling and gillnetting.

Common dolphin bycatch is a particularly important issue in Galicia Spain, via trawler fishing.

[38] The bycatch of short beaked dolphins in Galicia from May to September from 2001 to 2002, consisted of 394 individuals annually.

Depth was an important factor in bycatch, as incidental capture mostly took place along the continental shelf in water less than 300 m deep.

It is believed that the reason why the vast majority of bycatch consisted of males is because bachelor pods appear to be particularly abundant in Galicia from the May–October season.

This fact reinforces the hypothesis that common dolphins may be sexually segregated in the Northeast Atlantic.

If there was a ban on fishing in Galicia in waters than less than 250 m deep, and if there were seasonal closures, it is estimated that 78% of the dolphins would not have been caught.

[38] Common dolphins were abundant in the western Mediterranean Sea until the 1960s but occurrences there have tailed off rapidly.

In the US, they are a protected species and sometimes are caught by accident in some trawler nets as by-catch, though despite this they are still quite common throughout their range.

[1] The short-beaked common dolphin Delphinus delphis is listed globally on Appendix II[39] of the Convention on the Conservation of Migratory Species of Wild Animals (CMS).

The Mediterranean population of the short-beaked common dolphin is also listed on Appendix I,[39] as this population has been categorized as being in danger of extinction throughout all or a significant proportion of their range and CMS Parties strive towards strictly protecting these animals, conserving or restoring the places where they live, mitigating obstacles to migration and controlling other factors that might endanger them.

[42] On June 8, 2009, a mass-stranding event (MSE) occurred in Falmouth Bay, Cornwall, United Kingdom.

During the event, 26 common dolphins washed ashore, and about the same number floated back out to sea.

There were three other MSEs in the UK before this event, all of unknown cause, from the years 1915 to 1938, but with what are believed to be lower counts of stranded dolphins.

This behavior is consistent with wild common dolphins off of New Zealand, as they actively avoid swimmers.