No.065 · Mammals · Rare
Common dolphin
Delphinus delphis
A fast, playful dolphin with a tan-and-grey hourglass pattern on its sides, often racing in noisy schools and riding the bow wave.
When to look
July to October, mostly at day.
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Time of day
- Dawn
- Day
- Dusk
- Night
- Best time
- Summer to early autumn, roughly July–October, from a boat in the deeper water of the Irish Sea and Celtic Sea.
- Where in the game
- the Pembrokeshire coast (sea)
- Size
- Up to 2.5 m; calves are about 0.9–1.1 m at birth
- Weight
- Up to about 200 kg
- Lifespan
- Can live to about 30 years
- Population
- About 480,000 common dolphins across the shelf seas from southern Norway to Portugal in summer 2016 (Sea Watch Foundation)
- Status
- Least Concern (IUCN, Sea Watch Foundation)
Diet
Small schooling fish such as hake, horse mackerel, mackerel, sprat and sardine, plus squid, often herded by cooperating groups
Habitat
Mostly deep offshore water; around the UK it moves onto the continental shelf between July and October
Breeding
Mating and calving mainly May–September in the north-east Atlantic; gestation is 10–11 months, calves are weaned at about 19 months and the calving interval is usually 2–4 years or more
Field signs
- A tan-and-grey hourglass pattern along the sides
- A tall, pointed fin with a pale patch, and a slender beak
- Fast, splashy schools of 6–15 that leap, bow-ride and tail-slap
- Loud, high-pitched squeaks and whistles
Did you know?
- Schools of more than 100 have been seen in British shelf seas, and groups along the shelf edge can number several hundred.
- Common dolphins form strong social bonds: if one animal is injured, the others stay with it.
- In the UK there is a seasonal movement of common dolphins onto the continental shelf between July and October, and warmer seas have made them more regular around Shetland and Orkney (Sea Watch Foundation).
Moments worth waiting for
- Bow-riding school
A school of dolphins races in from the side, then surfs the bow wave, flashing tan-and-grey flanks just below the surface.
Photo tip
Sit at the bow of the boat with a shutter of 1/1500 s or faster and shoot wide when they surf the bow wave, or use a 100–300 mm lens for leaps. Watch the shadows the light makes on the flanks.
Be a good naturalist
Only go out with a WiSe-accredited or Pembrokeshire Marine Code operator. Be aware of dolphins at 100 m and keep at least 50 m away unless they approach you; slow to under 5 knots and keep a steady course. Let the dolphins choose to approach, never chase or cut through a group, and never swim with them.
The law
Legally protected in European, British and Irish waters (Sea Watch Foundation): all dolphins are on Schedule 5 of the Wildlife and Countryside Act 1981