Everything you need to know about dolphins – Part 2

Bottlenose dolphin jumping in Azores

How long do dolphins live?

In the wild most dolphins can live for a long time. Orcas may live for 70 years or more. Bottlenose dolphins can live for at least 40 years. In contrast, dolphins that are kept in captivity die much earlier than those living in the wild. For example bottlenose dolphins in average live until 20 years old in captivity.

For calculating dolphins’ age we have to pay attention to their teeth. Unlike humans, who lose their baby teeth, a dolphin will keep the full set of teeth it was born with for its entire life.

And also unlike human teeth, dolphin teeth grow larger by producing growth layers in the root. These layers are visible and distinct for each year of a dolphin’s life. Scientists are then able to determine how old a dolphin is by cutting the tooth in half and counting the growth layers that they see,   just as the rings of a tree. So, these layers are a very reliable way of  telling the age of most dolphin species.

 A good section of a bottlenose dolphin tooth
A good section of a bottlenose dolphin tooth. This tooth is from a male known to be 3.2-3.8 years old (Hohn A. et al, 1989).
A dolphin trying to bite another dolphin’s tail
A dolphin trying to bite another dolphin’s tail. This picture was taken from one of our catamarans (by Carine Zimmerman) and we can observe in detail the teeth.

How much do dolphins weight and measure?

Dolphins vary greatly in size, with their length ranging from 1,2 to 9 meters (4 to 30 feet) and their weight ranging from 39 kg to 10 ton (88 lbs. up to 22000 pounds).

The largest member of the dolphin families are usually referred to as whales such as orcas, false killer whales and pilot whales. The world’s smallest dolphins, commonly called Hector’s dolphins, include a subspecies called Maui’s dolphin.

Size comparison among some species of dolphins
Size comparison among some species of dolphins ( National Geographic)

Some smaller species of dolphin can be found traveling in and around coastal waters where they are less likely to face threats from potential predators, while larger dolphins may venture out further into the offshore ocean far from coastal waters (Srinivasan & Markowitz, 2010). But size does not always have a direct influence on where dolphins can be found living throughout the world, for example striped dolphins here in the Azores can be found offshore, and they are around 2m in length.

In addition to staying near coastal environments, small dolphins are also known to travel in large groups in order to protect themselves from predators. Predators for the dolphin species may include orcas and sharks (Srinivasan & Markowitz, 2010). 

Some sizes and weights examples of dolphins (Wikipedia):

1 Common Dolphin (Delphinus delphis) 1,7–2,4 m 70–110 kg
2 Striped Dolphin (Stenella coeruleoalba) 1,8–2,5 m 90–150 kg
3 Bottlenose Dolphin (Tursiops truncatus) 1,9–3,9 m 150–650 kg
4 Long-finned Pilot Whale (Globicephala melas) 3,8–6 m 1,8–3,5 t
5 Orca, Killer Whale (Orcinus orca) 5,5–9,8 m 2,6–9 t

In the Azores sometimes in the same trip we can see two species of dolphins at the same time, for example we can be with a huge group of Atlantic spotted dolphins and suddenly a few bottlenose appear interacting within the pod. Then we realise the incredible difference between this two species!

What do Dolphins eat?  

All dolphins are carnivores, eating fish and squid. Some dolphins eat crustaceans such as lobsters, shrimp, and crabs while some eat octopus and cuttlefish.  

Different species of dolphins focus on different foods and they have a variety of hunting styles. Sometimes we see  schools of fish from our boats and we can see “in situ” the typical images of a documentary, the feeding moment! 

Dolphins drive small schooling fish
Dolphins drive small schooling fish, like mackerel, close to the surface in tight bait-balls. (Ida Eriksson, Futurismo)

A dolphin has a three chambered stomach, similar to an ungulate (cow or deer). The mastication of their meal is taken care of in their first or also referred to as the fore stomach. Then, the majority of digestion is processed in the main stomach, or second chamber. And finally, the last section of their stomach, the pyloric stomach, takes care of the remainder of their digestion prior to the contents emptying into the intestinal region.  

Sagittal section of a dolphins stomach
Sagittal section of a dolphins stomach ( Perkopf, 1937)

And how they find the prey?

Dolphins use echolocation, which is a process that permits dolphins to send out sound waves that when they hit an object or a prey, they bounce back, allowing them to identify the location, shape, speed and size of such an object. Even they can tell the texture!! 

The amount of time it takes for the sound waves to come back helps them to determine the distance, as it takes longer the sound waves to return when there is more distance between the dolphin and that given prey. 

Echolocation of male indo-pacific bottlenose dolphin
Echolocation of male indo-pacific bottlenose dolphin (Zainuddin, 2016)

Discover more amazing facts on our first dolphins facts post

Written by María Huamán Benítez


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