Monday, 13 January 2014

Week 32: Bottlenose Dolphin (‘Tursiops truncatus’)

The bottlenose dolphin was @SpeciesofUK from 14th to 31st August, 2013.

Bottlenose dolphins are one of the most widespread mammals in the world. They can be found in every ocean, with the exception of polar waters.[1]

There are two species of bottlenose dolphin, the ‘common’ bottlenose and the ‘the Indo-Pacific’ bottlenose. The common bottlenose dolphin is native to the UK and is the subject of this blog.[2]

Bottlenose Dolphin
[Source: Flickr Creative Commons © Javier Corbo]

Bottlenose dolphins’ status as the ‘go to’ charismatic stars of aquarium shows has cemented their place in the popular imagination.[3] But there’s a lot more to these wonderful creatures than just fancy tricks…

The UK is at the northern edge of the bottlenose dolphin’s range.

Bottlenose dolphins inhabit tropical and temperate coastal waters around the world. UK waters are about as far north as they can be found.[4]

Bottlenose Dolphin Distribution
[Source: Wikimedia Commons © The Emirr]

Bottlenose dolphins around the UK keep fairly close to the coast, frequenting bays, estuaries, sounds, open shorelines and large, estuarine rivers.[5] The Moray Firth and Cardigan Bay are particular hotspots.[6]

Bottlenose Dolphins
[Source: Flickr Creative Commons © jeffk42]

Elsewhere, bottlenose dolphins visit deeper water. Deep-water bottlenose dolphins tend to breathe once every couple of minutes, compared to about twice a minute for their coast-hugging cousins.[7]

The longest a bottlenose dolphin can hold its breath is around five to seven minutes.[8]

A Bottlenose Breath
[Source: Flickr Creative Commons © Vanessa Stephen]

Bottlenose dolphins are perfectly adapted for life in the fast lane.

The bottlenose dolphin is 'fusiform' is shape, meaning it is tapered at the head and tail and lacks external features like hair, ears and limbs.  This makes it faster in the water.[9]

The bottlenose dolphin also has a telescoped skull adapted for swimming and breathing in a marine environment.[10]

It has two front flippers (for steering), a tall curved dorsal fin (for a keel) and horizontal 'flukes' on the tail (for propulsion).[11]

Flippers, Dorsal Fin and Flukes
[Source: Flickr Creative Commons © spencer77]

Bottlenose dolphins are typically black to light grey in colour with a white belly, meaning they are camouflaged against both light sunlit surfaces and dark ocean depths.[12]

At birth a bottlenose dolphin weighs 14 to 20kg. Adult males weigh about 500kg, twice the weight of an adult female.[13]

Bottlenose dolphins also have distinctively curved mouths which gives the appearance of a friendly, permanent smile.

Dolphin "Smile"
[Source: Flickr Creative Commons © Javier Corbo]

Bottlenose dolphins are of course mammals, meaning they have had to evolve some nifty features to adapt to a life in water.

All mammals have hair. Bottlenose dolphins are no different – their babies have whiskers on their upper jaws. However, these hairs fall out soon after birth.[14]

They also have to surface regularly to breathe. This poses a difficulty with sleeping. If bottlenose dolphins were to fall into a deep sleep, like we do, they wouldn’t know when to surface and take a breath. So bottlenose dolphins are never fully asleep.[15]

Bottlenose dolphins instead allow half of their brain at a time to 'sleep,' while the other half of their brain stays awake. This allows them to continue to control their breathing.[16]

Scientists have studied this half-asleep/half-awake state using electrodes and found that dolphins are in this state for about eight hours a day.[17]

Dolphins at Sunset
[Source: Flickr Creative Commons © Angell Williams]

Bottlenose dolphin courtship is a complex, expressive and sometimes aggressive, affair.

Bottlenose dolphins are polygamous. Males sometimes court females individually or sometimes form alliances and search for females as a group.[18]

When an alliance of males finds a group of females, they separate them out and drive them from their home. In these cases it can be weeks before the female becomes receptive to mating.[19]

Males that court females individually tend to stay in their home range, wait for an oestrous female to come along and then court her.[20]

Bottlenose courtship is famously expressive. The male arches his back, postures, strokes/nuzzles the female, claps his jaws and yelps.[21]

Bottlenose dolphin copulation occurs belly to belly facing the same direction, although they do also try out different positions...[22]

A male bottlenose dolphin reaches sexual maturity between eight to thirteen years but doesn't typically breed until about twenty years of age. Females on the other hand reach maturity between about five to ten years.[23]

Gestation lasts about twelve months and each pregnancy produces one calf. Females nurse their young from nipples on each side.[24]

Bottlenose Dolphin Calf
[Source: Flickr Creative Commons © Mark Interrante]

A mother bottlenose dolphin produces a very rich milk for her calf. The calf has a specially adapted tongue so it can form a straw shape and not ingest saltwater.[25]

Bottlenose dolphins reproduce every three to six years and females can reproduce well into their late forties.[26]

Bonding between mother and baby dolphins is an important stage in a young dolphin’s life.

A bottlenose dolphin calf learns to ride the pressure waves alongside its mother during its first few days. The mother helps it to stay close to her.[27]

Mothers and Calves
[Source: Flickr Creative Commons © Bryce Bradford]

A mother and calf surface and breathe in synchrony. This is an important feature of bonding. Synchronised breathing continues into adulthood. Adult bottlenose dolphins surface in synchrony when they're under stress, for example when disturbed by boat traffic.[28]

Bottlenose Dolphin Affection
[Source: Flickr Creative Commons © Javier Corbo]

Bottlenose dolphins participate in allo-maternal care, meaning females help care for each other's calves and protect them from predators.[29]

Bottlenose dolphins are very social animals.

They communicate with a startlingly complex system of squeaks and whistles.[30] In fact, bottlenose dolphins can even call each other by 'name,' as this video explains:

Schools of bottlenose dolphins have also been known to come to the aid of an injured dolphin and help it to the surface.[31]

They are extremely effective hunters.

Bottlenose dolphins are experts at echolocation, often hunting in teams and tracking prey by making up to 1,000 clicking noises per second.[32]

Echolocation works because the clicking sounds bounce off objects and return to the dolphin, revealing the location, size and shape of their target.[33]

Bottlenose dolphins have 80-100 cone-shaped teeth which they use for trapping their prey. They swallow their food whole without chewing it.[34]

Bottlenose Teeth
[Source: Flickr Creative Commons © Javier Corbo]

Bottlenose Skull
[Source: Flickr Creative Commons © fossilmike]

Bottlenose dolphins feed on fish, plus some shrimp, eels and squid. They're clever enough to follow fishing boats in the hope of dining on leftovers.[35] They mainly feed along coastal waters although can also feed in the open water and on bottom-dwelling fish.[36]

Regrettably, bottlenose dolphins are under threat themselves.

Bottlenose dolphins were once widely hunted for meat and oil (used for lamps and cooking). Today, they're threatened by fishing for other species, like tuna.[37]

A real danger for bottlenose dolphins is becoming mortally entangled in nets and other fishing equipment.[38]

Strange but true…
Bottlenose dolphins have been observed to breach up to a massive 16 feet out of the water.[39]

Dolphin Breaching
[Source: Flickr Creative Commons © Jual]

[28] BBC Wildlife 31:3

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