Whale of the Month - Common Dolphin

Species fact file

Common names: short-beaked common dolphin

Icelandic name: léttir

Scientific name: Delphinus delphis

Family: Delphinidae (dolphins)

Max length: 2m (males), 1.93m (females)

Distribution: Temperate and tropical waters worldwide

The common dolphin is the most numerous dolphin found in the temperate waters of the Atlantic and Pacific. There are an estimated 467,000 in the European Atlantic, with a further 5,200 in the Mediterranean Sea. Although the Bay of Biscay and coastal waters around France and Spain host the greatest number of dolphins, they are occasionally seen further north in waters around Iceland and Greenland.

Common dolphins are found in a range of marine environments across the globe, and as such they hunt a wide variety of prey. They can dive up to 200m underwater for small deep-water fish and squid, as well as hunting for shallower schooling fishes like herring and sardines. In general, common dolphins show a preference for one kind of prey. Their preferred prey varies region-to-region depending on what is most available there, but they typically choose fatty, high-energy species. These preferences are to an extent flexible. If there is a decrease in their primary prey – for example, due to overfishing – common dolphins can switch to a new species.

Like most dolphins, common dolphins are very social, and it is not unusual for them to live in groups a hundred strong. They are often seen in even larger aggregations called ‘superpods’ which may consist of over a thousand dolphins travelling and hunting in close proximity to one another. These groups form when multiple pods – usually 20 to 30 dolphins – join together. You can watch some footage of a common dolphin superpod in Monterey Bay here.

How common dolphins form their pods is a question that remains largely unanswered. For many other dolphin species, pods are extended family units – but common dolphin pods don’t consist of closely related individuals. In the Northeast Atlantic, close relatives are usually found living in the same are as one another, so common dolphins may not travel too far from the pod they were born into.

Travelling in large groups over long distances, common dolphins are able to maintain contact with their companions by altering their vocal behaviour. When the group is spread out over a wide area, such as during travelling, the dolphins call to one another frequently. On the other hand, when foraging in a more closely aggregated group, they reduce the frequency of their vocalisations.

On multiple occasions, common dolphins have reproduced with another species of dolphin to produce hybrids. Hybridisation is not an unusual occurrence amongst dolphins. In fact, one species of dolphin, the Clymene dolphin, evolved as a result of cross-breeding between spinner and striped dolphins.

In one particular region of Greece, hybridisation between common and striped dolphins seems to be especially frequent, with at least 15 confirmed hybrids. These hybrids are fertile and can produce offspring with other hybrids as well as either parent species.  

Although they have a fairly specialised diet, common dolphins do have the ability to switch from one primary prey species to another. Therefore, they may have some resilience to changes in marine ecosystems as different prey populations fluctuate in size. However, they face other threats from human activities. The species as a whole is classed as Least Concern by the IUCN, but the sub-population in the Mediterranean has been declining since the 1970s and is currently listed as Endangered. In the Mediterranean, common dolphins face the combined effects of habitat degradation with increasing human coastal developments, chemical and plastic pollution, bycatch, and intensive fishing of multiple prey species.

In addition to this, common dolphins will have to adapt to life in a warming ocean. The effects of climate change on this species are not yet fully clear but it's likely that their global distribution will shift towards the poles as sea temperatures continue to rise. There is some evidence that this change is underway already: a long-term monitoring project off the coast of Scotland has seen a marked increase in the frequency of common dolphin sightings. It is possible that this occasional visitor to Icelandic coasts may become a more familiar sight in years to come.

Learn more about...

The endangered Mediterranean sub-population and hybridisation with striped dolphins

How common dolphins can change what they eat in response to changes in their ecosystem