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Dusky Dolphins of New Zealand

Dusky Dolphins of New Zealand
A dusky dolphin performs a back-flip. kaikoura, New Zealand. 
© Colin Munro Photography
A dusky dolphin performs a back-flip beside our boat.

Dusky dolphins (Lagenorhynchus obscurus) are possibly the most playful, and certainly one of the most – if not the most – acrobatic of all dolphin species. An encounter with a pod of duskies is an experience that stays with you for a long time. I’ve been fortunate enough to see dusky dolphins on a number of occasions, always around New Zealand, although they are widely distributed in cooler, coastal waters in the southern hemisphere. Kaikoura Peninsula, in the south-eastern corner of South Island, is famous for the large numbers of cetaceans that are found there, including pods of dusky dolphins, and it is here that I have had the best interactions with duskies. Many dolphin species will interact with boats, with groups changing direction to bow-ride for a few minutes. When it happens, no matter how many times you may have witnessed dolphins bow-riding, it’s still an uplifting experience when it happens. But duskies are something else! They don’t simply bow-ride; when they decide to play with a passing vessel, it’s like the the acrobats from Circus Soleil have teamed up with a bunch of olympic gymnasts to put on a show for you. It is impossible to watch and not be convinced that they are performing simply for the pleasure of showing off and letting you know just how good they are. While travelling at speed a dolphin will fly 3 metres high, performing a back-flip, to tail-slap hard on the water’s surface. I’ve watched three dolphins leap high in the air, describing a perfect arc, each dolphin precisely following the path of the one less than a body’s length in front.

Dusky dolphins leaping, Kaikoura.
© Colin Munro photography
Synchronised leaps of dusky dolphins

There is also a tangible sense of competition between them. Groups of young male dolphins, five or six abreast, will suddenly sprint 50 metres, clearly racing one another.

dusky dolphins racing through the water, Kaikoura, New Zealand
Dusky dolphins race alongside our boat

Like many other species of cetacean, including sperm whales, dusky dolphins are attracted to Kaikoura because of the rich feeding in in deep water nearby. Kaikoura Canyon, a 60 kilometre long underwater trench, comes to with 1000 metres of the shore, but plunges steeply to up to 1.2 kilometres in places. Recent studies have shown that Kaikoura Canyon holds some of the greatest concentrations of biomass of deepwater species of anywhere in the World (De Leo, et al., 2010) with biomass concentrations up to 100 times greater than similar deepwater habitats. Within deeper waters, a phenomenon known as the DSL, or Deep Scattering layer occurs. This refers to the effect on the echo sounders used on ships to detect the depth of the seabed. A layer occurs mid-water that reflects the acoustic signal of these sounders. This reflection, or scattering, is caused by the gas-filled swim bladders of millions of fish, mostly types of lanternfish, the most abundant fish in the mesopelagic zone (the oceans between around 200-1000m depth, sometimes called the twilight zone). The layer also contains creatures such as squid and crustaceans, but they have no swim bladders, so do not contribute to the bounce of acoustic signals. This layer is where the dusky dolphins are feeding. This dense aggregation of fish, squid and mid-water crustaceans attracts predators, including the dolphins. This living layer is not static however, it undergoes a vertical migration of hundreds of metres every day, rising towards the surface at night, then descending back into the depths as the sun rises. Dusky dolphins feed in this layer at night. They are believed capable of diving to below 150 metres, but prefer to feed when the layer rises to within 130 metres of the surface (Benoit-Bird et al. 2004).

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If you enjoyed this article maybe consider subscribing to my blog. I will hopefully complete a book on ocean life in the coming months, you can learn more about it and follow its progress by subscribing to my mailing list here. The dolphin pictures shown here are available as fine art prints. These are available as stretched canvas, canvas wraps, flat canvas, dye-infused aluminium prints and acrylic on alumimium in a range of sizes and crops. They can be ordered directly from my website colinmunroimages.com. Default printing is my Bay Photos professional fine art printers in California. For orders from the UK, contact me directly and these can be supplied by Loxley professional printers in the UK. It can also be downloaded as a digital file, for private or commercial use, in a range of file sizes.

References

Benoit-Bird, Kelly & Würsig, Bernd & Mfadden, Cynthia. 2004. Dusky dolphin (Lagenorhynchus obscurus) foraging in two different habitats: Active acoustic detection of dolphins and their prey. Marine Mammal Science. 20. 215 – 231. 10.1111/j.1748-7692.2004.tb01152.x.

De Leo Fabio C., Smith Craig R., Rowden Ashley A., Bowden David A. and Clark Malcolm R., 2010. Submarine canyons: hotspots of benthic biomass and productivity in the deep sea. Proc. R. Soc. B.2772783–2792

Common dolphins, fastest mammal in the sea

Common dolphin (Delphinus delphis) swimming at high speed. Colin munro Photography

Common dolphin (Delphinus delphis) swimming at high speed. Colin munro Photography

Common dolphin (Delphinus delphis) swimming at high speed, just below the surface.

What is the fastest marine mammal? There are a number of pretty speedy guys in the water. It’s been calculated that when an orca, weighing up to five tonnes, breaches this requires an exit speed of around 40kph. That’s around the same as the maximum speed attained by Usain Bolt in a 100 metres race. Only he doesn’t weigh five tonnes…and he’s not doing it underwater. In 2009 french swimmer Frédérick Bousquet set a World record 50m freestyle sprint, with an avergae speed of 8.6kph. A lot faster than you or I, but never gonna outswim an orca; orcas can, in fact touch 50kph when they want to. Perhaps surprisingly, given that they weigh upwards of 150 tonnes, blue whales are also pretty zippy, also able to get the needle up to 50khp when in a hurry (why would blue whales be in a hurry?). However current data suggests that the fastest dude on the block is the common dolphin (Delphinus delphinus). These guys can reach 64kph (40mph). According to the Guiness Book of records that’s a whisker slower than the fastest racehorse (Winning Brew, 2008) over 400 metres (two furlongs). I’ve owned cars that struggle to do that on hills.

It is hard moving fast through water compared to air, so how do they do it? In 1936 zoologist Sir James Gray looked at this and concluded that dolphins simply shouldn’t be able to generate sufficient power to move them through the water as fast as they appeared able to do. This became known as Gray’s Paradox. It is now believed that the hydrodynamic shape of dolphins greatly reduces form drag, and thus the power required. There is also some evidence that the dolphin’s soft skin, which is continually shed, reduces friction drag. Even so, that a dolphin can travel as fast as a thoroughbred racehorse, through a medium almost 800 times more dense than air, is pretty impressive.

How many common dolphin species?
Until the 1960s all common dolphins were considered one single species. Genetic studies have indicated that there are probably at least two, possibly three distinct species. These are the short-beaked common dolphin (Delphinus delphis) which is the species most likely to be encountered in british waters; the long-beaked common dolphin (Delphnus capensis), and possibly a third species, the arabian common dolphin (Delphinus tropicalis) although many marine biologists consider this a subspecies of the long-beaked common dolphin.

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Colin Munro

Common Dolphins, mother and calf

Common Dolphins, mother and calf

Mother and calf common dolphins (Delphinus delphis) swimming in close harmony. Colin Munro Photography. Image No. MBI000335.

Mother and calf common dolphins (Delphinus delphis) swimming in close harmony. Image No. MBI000335.

 These pictures were taken during a recent trip to look for blure sharks (Prionace glauca) off the north coast.  Although we did find one blue, we had no luck with pictures (next time!).  However we did come across a large group of common dolphins (Delphinus delphis) feeding.  Each summer substantial numbers of commons dolphins can be found around the coasts of Devon and Cornwall as they follow the mackerel shaols.  Hopefully I’ll be adding to these images this summer.  As ever, these images can be licenses for reproduction and are also available as fine art prints.  Email me , telling me the image number and what you require for further details. You can also search for additional images either from my main website homepage or using my Photoshelter website. Links for both are given in the sidebar.

Common dolphins (Delphinus delphis) swimming, showing tooth rake marks on back. Colin Munro Photography, Image No. MBI000333.

Common dolphins (Delphinus delphis) swimming, showing tooth rake marks on back. Colin Munro Photography, Image No. MBI000333.

 

Common dolphins (Delphinus delphis) swimming, head on. Colin Munro Photography, Image No. MBI000339.

Common dolphins (Delphinus delphis) swimming, head on. Image No. MBI000339.

 

Common dolphin (Delphinus delphis) swimming at high speed. Colin Munro Photography, Image No. MBI000337.

Common dolphin (Delphinus delphis) swimming at high speed. Image No. MBI000337.