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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

Shortfin makos, the fastest shark of all.

Shortfin makos, the fastest shark of all.

A Mako shark make a half-hearted attempt to grab a cape petrel. Copyright Colin Munro Photography

A Mako shark make a half-hearted attempt to grab a cape petrel.

When one thinks of sharks one thinks of sleek, powerful predators that appear to cruise effortlessly but are capable of dazzling bursts of speed when they attack prey.  This image of the shark is exemplified by the shortfin mako.  We know makos are fast, but how fast?  Many sources will tell you it is capable of speeds of 74kmph or greater.  The truth is a little less dramatic.  We now know that around 35kmph is probably the maximum speed of any fish through water, and that makos are probably capable of speeds around 30kmph, which still puts them right up there among the ranks of the elite fish speed merchants, and around four times faster than any human (for a more detailed, scientific account you read my marine-bio-images.com blog XXX).  Makos are generally accepted as being the fastest of all sharks, and with that powerful, missile-like shape, they are definately built for speed.  I have yet to get in the water with a mako – it is one of my goals for this year.  In the meantime I have an unexpected surface encounter off Kaikoura to savour. Kaikoura, as many of you will know, is a small town on the north east coast of New Zealand’s South Island.  It is famous as one of the best places in the World for whale watching, especially sperm whales.  It also came the wider world’s attention in November 2016, when the region was struck by a 7.8 magnitude earthquake, cutting off road and rail links to the town, uplifting areas of seabed and causing a localised tsunami up to 7 metres in height. When we visited in February 2017, road connections were still disrupted and whale watching boats had difficulty operating due to sea level changes affecting there berthing alongside.  The town, highly dependent on tourism, was suffering markedly.  We were not there to look for whales though, we were looking for dolphin and albatross. Kaikoura may be most famous for whales, but it is also a fantastic place to see many species of albatross up close, and it was albatross and dolphin we were there to see.

Albatross squabble over food. Kaikoura, New Zealand. Copyright Colin Munro Photography

Albatross squabble over food. Kaikoura, New Zealand.

Whilst the big whales grab most of the international headlines, the sheer drama of seeing several species of albatross up close – really close – soaring, wheeling and plunging down to feed, is pretty hard to beat.  Nor was it just the albatrosses and giant petrels that noticed the food  in the water.  The scent of chum in the water attracted in predators from below also.  A dark triangular fin broke the surface and began weaving through the wary seabirds.  The shark was a juvenile mako, approximately 5-6ft (1.5-1.8m) long. Whilst clearly drawn towards us by the fish scraps in the water, it then became interested in the birds splashing around.

An albatross warily eyes the mako shark, whilst a westland petrel flaps away from the sharks path. Copyright Colin Munro Photography

An albatross warily eyes the mako shark, whilst a westland petrel flaps away from the sharks path.

The great albatrosses eyed the shark with a mixture of wariness and belligerence; with a wingspan probably exceeding the length of the shark they may have seemed a little large to tackle.  The smaller petrels were more anxious.  It made a grab for one cape petrel that did not move out of its path fast enough, but the attack seemed have hearted and the petrel skittered away easily enough.  There was probably enough fish remains floating in the water to keep the shark happy. Makos will occasionally take seabirds, but mostly feed on pelagic fish species such as mackerel, herring and anchovies.  Larger individuals have been found to have young seals and even common dolphins in their stomachs, as well as billfish such as marlin.  Common dolphins and marlin are both renowned for their speed, so whilst it is possible that these were injured individuals snapped up by the mako, it is also these fell prey to the makos lightening speed.

Graham, J. B., DeWar, H., Lai, N. C., Lowell, W. R., & Arce, S. M. (1990). Aspects of shark swimming performance determined using a large water tunnel. Journal of Experimental Biology, 151(1), 175-192.