Poor Knights marine reserve

the mystery of the social sting rays
by Dr J Floor Anthoni (2007)
www.seafriends.org.nz/issues/res/pk/stingrays.htm


Stingrays have always fascinated people, not just by their strange shapes and way of swimming, but mainly by their bad reputation of stinging people. Indeed their sting can be quite painful, and explorer Steve Irwin was killed by a sting piercing his heart. However, my experience with stingrays has been quite the contrary: they are gentle giants with enough intelligence to be playful. In New Zealand we have three species, each of which has a unique character and lifestyle. My experience has shown that you do not need to fear the stingrays of the Poor Knights.
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Three species, three kinds
In New Zealand we have three species of stingray, the eagle ray, the short-tailed stingray and the long-tailed stingray. It so happens that all three can be encountered on the poor Knights, an unusual coincidence because the eagle ray is mainly a coastal and estuarine stingray, and the long-tailed stingray has reduced its range considerably in the past decade, and can now mainly (only?) be found on the Poor Knights. It has disappeared from coastal waters and is not found south of Auckland, although identification guides still mention its southern range as Cook Strait (Wellington) and its habitat as estuaries and muddy areas.

Sting rays belong to the 'primitive' cartilaginous fishes, as opposed to the more 'modern' bony fishes, but in evolution they have in fact become quite advanced. For instance they have internal fertilisation and bear their young live. A female stingray has usually only two babies, which after birth, have to fend for themselves. Contrary to the 'modern' fishes, whose offspring float away on ocean currents, a stingray's babies are born where the mother lives. This may explain why populations can maintain themselves well in remote places like the Poor Knights Islands.
The difference between males and females can easily be seen as males have two claspers trailing under their tail flap.
 
 
The eagle ray (Myliobatis tenuicaudatus)
The NZ eagle ray (Maori: Whai keo) can be distinguished quite easily by its whip-like tail (tenuicaudatus=thin-tailed) looking like a car antenna. At the base of this tail is of course found its sting, but also a small back fin, which is absent in the two other species. The eagle ray has a head and shoulders and pointed wings. It is usually grey to black above with a white belly but can also be yellow-green to brown on top.
Eagle rays are found on both the North and South Island, mainly in coastal areas and estuaries. It feeds mainly on molluscs, ranging from small cockles, to scallops (coquilles St-Jacques) and on large snails like the Cooks turban snail (Cookia sulcata). The eagle ray is generally shy and not playful. It is entirely harmless and can be approached as far as it would let you.

On the Poor Knights, eagle rays are not very common. They must be feeding from large snails like the Cooks turban snail, but I've never seen broken fragments of such. The Poor Knights does not have cockles or scallops, the preferred food of eagle rays.
 

just-born baby eagle ray and mature long-tailed stingray
f041228: on left a just-born baby eagle ray, about 40cm across. It is dwarfed by the long-tailed stingray that startled it when passing over. Baby eagle rays are very shy, but so cute with their blue spots.
eagle ray (Myliobatis tenuicaudatus)
f021002: the eagle ray (Myliobatis tenuicaudatus) has a pronounced head. It also takes good care in burrowing itself well, to remain invisible to predators like orca.
eagle ray (Myliobatis tenuicaudatus)
f034909: typical elegant flight of an eagle ray. This one is yellowish rather than grey to black. It could well be albino.
eagle ray (Myliobatis tenuicaudatus)
f034912: The Poor Knights are inhabited also by a tribe of yellow eagle rays like this female. 

 
 
The short-tailed stingray (Dasyatis brevicaudata)
The short-tailed stingray could well be the most common one on the Poor Knights and outer island of the east coast of the North Island, but it is not common on the South Island. In places it grows as large as a man, standing with outstretched arms, as can easily be measured from the large imprints found in the sand. Bigger ones still have been seen (and caught) with a wing span of up to 3.5m!
The short-tailed stingray is easily attracted to bait, and often appears when fishermen gut their catch. Surprisingly, it can be hand-fed, as it does not home in on its quarry by eyesight but by smell. It is intelligent and learns quickly. Divers usually see the short-tailed stingray swimming gently over the kelp as in the first photo, but it can move very fast. It can speed in the opposite direction with a loud bang, caused by water cavitating on its wing. In order to achieve this feat, it must be enormously strong.

As scavenger, the short-tailed stingray must be able to find food easily from occasional deaths in schooling fish.
 

short-tailed stingray (Dasyatis brevicaudata)
f034915: this short-tailed stingray (Dasyatis brevicaudata) is well aware of the photographer who quietly let it pass by. Most would have veered away by now.
short-tailed stingray (Dasyatis brevicaudata)
f038733: a male short-tailed stingray shows its belly with nostrils, mouth and gill slits. Trailing under its tail flap one can see two claspers by which males are identified. Notice that short-tailed stingrays have a grey margin underneath.
wounded short-tailed stingray (Dasyatis brevicaudata)
f022505: short-tailed stingrays are often encountered while cruising in the warm layer just under the surface. That is where they can be wounded by propellers, as happened to this poor stingray. Fortunately they are able to survive large wounds.
albino short-tailed stingray (Dasyatis brevicaudata)
f020509: several albino short-tailed stingrays can be encountered at the Poor Knights Islands, like this female.
short-tailed stingray (Dasyatis brevicaudata)
f029223: a medium-sized short-tailed stingray on the shallow sand in Nursery Cove. Notice its squat shape and short tail with one or two barbs.

 
 
The long-tailed stingray (Dasyatis thetidis)
The long-tailed stingray is dark olive to black on top and entirely white underneath without a grey margin. It is immediately identified by its very long tail, twice the length of its body. This stingray stays much smaller than the short-tailed stingray, reaching a wing span of about 1m. It can be approached easily as it is not aggressive. At the Poor Knights, these stingrays can be found resting by day in the shallow sand of Nursery Cove and the Labrid Channel.

 
male long-tailed stingray (Dasyatis thetidis)
f026017: a male long-tailed stingray (Dasyatis thetidis) in flight.
female long-tailed stingray (Dasyatis thetidis)
f041227: a large female long-tailed stingray turns away from the photographer, carefully avoiding her tail to make contact.
pregnant female long-tailed stingray (Dasyatis thetidis)
f012726: a highly pregnant female long-tailed stingray, one baby on each side.
pregnant female long-tailed stingray (Dasyatis thetidis)
f012729: close-up of pregnant stingray shows that the pregnancy bulge is quite large.
a snorkeldiver is allowed to touch a female long-tailed stingray
f029212: a snorkeldiver is allowed to touch a female long-tailed stingray, but her tail is raised already for gently turning away.
two long-tailed stingrays on shallow sand
f041511: two long-tailed stingrays on shallow sand and a snorkeldiver passing cautiously over.



 
Socialising in the archways
The Poor Knights have become famous for their socialising stingrays, particularly those seen in Northern Arch. At one time I counted 53, and on one of the photos below one can count as many as 26! But what are they doing there?
There have been wild speculations about what brings these stingrays to Northern Arch. It may have something to do with mating, as one finds most in the mating months from September to November. But one does not find them in other arches, except for Tie-dye Arch in The Squires, a considerable distance away. Some think that they migrate from far away on the mainland, to return later after mating. But for this, their numbers are not large enough.

In recent years, scientists have made exaggerated claims about sharks' and rays' ability of sensing electrical currents, to the extent that these animals here in New Zealand could sense a car battery being dumped in the sea at the other end of the ocean (10,000km away). This ability, it is reasoned, enables them to read an internal compass to navigate from the mainland to the Poor Knights and back.
 

stingrays in Northern Arch
f011933: five stingrays in Northern Arch on a day with poor visibility. The one in centre is an albino.
short-tailed stingrays in Northern Arch
f020507: looking up to the entrance, one can count 9 silhouettes.
short-tailed stingrays in Northern Arch
f020528: this photo, taken with a 50mm lens, shows 26 stingrays in Northern Arch.

The real reason for this behaviour is quite simple although also quite unbelievable. Stingrays do not form pair bonds, and must therefore pair up for mating, at the beginning of every year. Here in NZ, it happens in spring, in the months September to November (not entirely sure of this). Having dived on the Poor Knights since 1978, I have witnessed how it happened. In the beginning, there were no stingrays in Northern Arch, but then one day it began with only a couple. I observed that they were teaching themselves how to hang-glide in the rising current. Stingrays have no swim bladders, so they sink as soon as they stop swimming. But here they discovered that they could stay suspended, without swimming.

The next year there were a few more, and the year thereafter a few more, until one day I counted 53, half of whom were not quite capable of hang-gliding yet, as they tried to figure out what the others were doing. The diagram below shows the situation at Northern Arch, where currents rise over the sil at the bottom, causing uplift. Along the sides, the currents speed up, which can in theory also support hang-gliding, but this is very difficult indeed. The best positions are somewhere towards the lower middle, and there is some competition for these spots.

When the current stops, the fun is temporarily over, and one can see them all just flapping around. No sooner has the current returned, and the adept ones, take up their positions again. In Tie-dye Arch, which is fully submerged and has a n extensive flat bottom, the currents distort mainly at the top, where they exit. So one finds the stingrays hovering here.
 

stingrays hang-gliding in Northern Arch
Diagram showing the uplifting current in Northern Arch, which allows stingrays to hang-glide in place. In Northern Arch there is more opportunity for hang-gliding than in Tie-dye Arch.
stingrays hang-gliding in Tie-dye Arch
In Tie-dye arch, the water velocity distorts most near the top, as the archway is fully submerged. So one finds stingrays hovering near the top where the currents provide uplift.
Nothern Arch promontory
f012701: the promontory of Northern Arch runs across the current, which increases the current through the archway.
gannet colony and Tie-dye arch
f218819: Tie-dye Arch is located under a gannet colony, with its northern entrance on right. The archway is fully submerged.

Hovering in the current, or hang-gliding is not unique among stingrays, although their aerodynamic shape is just so perfect for this, with large horizontal planes. Many other fish species practice it, such as butterfly perch, blue maomao, pink maomao, snapper, tarakihi, giant boarfish and undoubtedly many more. For the photographer it offers a unique opportunity to obtain a stationary shot of otherwise ever moving fish.

The photo below shows four young giant boarfish hang-gliding behind a rocky wall at 20m depth. The biggest one just detached itself from the strict formation that lined up their eye patches, as it comes for a closer inspection. Notice their long backfin rays that shrink as they grow. Notice also their large breast and hip fins, acting as ailerons (wing flaps). There is also this poor tarakihi who by his lonesome sought company with the boarfish on account of their superficial resemblance by a dark patch. The tarakihi is closely related to the porae, both having long breast fins that could act as ailerons.
 

f006124: four young giant boarfish (Paristiopterus labiosus) and one tarakihi (Nemadactylus macropterus) hovering in the current deflected by the rocky wall on right. Note that young boarfish have long fins that shrink as they grow older!


Other encounters
As an underwater photographer, I am privileged to be able to document many experiences. As every photographer knows, what makes it to film is only a small part of the total experience, and there remains much just recorded by the grey matter in one's mind. Yet these experiences need to be told, so that a more complete picture emerges of diving in New Zealand and the Poor Knights.

 
The smart kingfish and the decoy ray
In Nursery Cove I was watching a young kingfish, no larger than 50cm, hunt a school of young koheru. In this he was spectacularly unsuccessful, as these fish dodged him and even out-swam him at every lunge he made for them. This in itself is astounding, because the laws of physics insist that small fish cannot outswim larger ones. Yet they did, and with a wide margin.

When koheru are catching morsels of food, they are in a loose schooling formation, but as soon as panic arises, they group into a tight oval ball which acts like a much larger fish, propelled by a mysterious jet motor. The principle of a jet motor is that its thrust equals the amount of water jetted out, multiplied by speed. Apparently the little fish, by moving their tails and bodies in unison, are capable of pumping a strong thrust that moves them forward with least friction, while also satisfying the laws of physics for bigger fish. They outswim the larger kingfish as it is not jet-propelled.

This shows clearly why it is necessary for kingfish to hunt in packs, for this causes confusion amongst its prey, and like wolves, the kingfish can surround the school of little fishes.

Now, this little Kingfish became visibly tired and disappeared, only to reappear hiding underneath a long-tailed stingray (see photo). His plan would have worked had the stingray not been annoyed with this object underneath, that prevented it from landing on the sand. So it began to shear tightly over the stalked kelp, trying to rub the little blighter off. All this foiled the little kingfish' plan, although he was nearly successful.
 

f023206: a young kingfish uses a long-tailed stingray as trojan horse to attack a school of koheru, shown as light patches in the distance.
How can little fishes outswim much larger predators? Could it be that by swimming in close quarters, they produce a jet motor, as yet unknown to Man?

 
The giant short-tailed stingray
During a lonely dive at the Mokohinau Islands, at the northernmost tip of Burgess, where an exposed canyon loops around a large rock, it was rather dark due to all the foam on top. And as I swam over the egg-sized loose pebbles, the bottom changed into smooth rock, and then pebbles again. It took me quite a while to realise that this smooth rock was rather unusual. As I turned around, I saw that I had been swimming right over the back of a gigantic stingray, so big that I could not believe (comprehend, really) what I saw.
It was a large female short-tailed stingray with a wing span of at least 3.5m! She was not concerned with my presence at all, as I approached cautiously from behind, where I could film only part of her due to all the suspended bubbles and consequent darkness. The base of her tail was thicker than a dive tank. Her barb was 60cm (2ft) long, and at the base of this spine I could not get my index and thumb to meet. Such a giant is perhaps over 100 years old, and one would hope she would survive another century. Imagine such a friendly giant living at the Poor Knights, always sleeping in her preferred den, and often visited by divers?
I'd like to share with you the internal turmoil inside me when I finally realised what I was looking at. First I swam squarely over the back of this stingray, thinking it was a rock. Then 4 metres further, it dawned upon me that the smooth rock I saw, was strange. I stopped and looked back and I didn't see the stingray. I backtracked to touching distance and still didn't see it. My mind could not see it because it didn't match any of the previous images of stingrays in my mind. I couldn't see it because it was so big. Yet, the tail was there, like one that stingrays have. Then finally my brain began to accept a new dimension and slowly I could see the rock for a sting ray. And guess what? A wave of emotion overcame me - not fear at all - but a kind of emotional discharge like when firmly held belief is proved wrong, and finally accepting the truth. I began to snotter for no apparent reason.
Apparently our brains are resisting anything that overturns previous experiences. Apparently our eyes can see only what we expect to see, and as soon as it differs by a whole dimension, we can not see it. And when we finally come to grips with it, it goes with strong emotions. Think about this when going into a new environment, like diving.

 
The stingray who fell in love with a diver
My buddy and I were diving on the sand on the southern end of The Labyrinth when we noticed three young female long-tailed stingrays on the sand. Nothing special, except that these pointed their stiff tails right up, instead of holding them down over the sand. Ignoring them, we busied ourselves filming a sharp-nosed pufferfish, when one of the rays came really close.
She snuggled up to Bruce, touching and caressing him, and we both returned the favour. The other two stingrays also came closer for a cuddle. What did we deserve for such affection? These female stingrays still pointed their tails stiff up, and snuggled up against us, not planning any time soon to leave. What was going on?

Back on the boat we couldn't get over our surprise and excitement, trying to explain what we had experienced. The closest explanation is that these young female stingrays were somehow on heat and mistook us for mating partners. Hunters have often reported that young does (female deer) in their first season on heat, come snuggling up to them, quite overwhelmed by feelings inside, yet not knowing what to do. Perhaps this was also the case with our stingray girls?
 
 
Riding a stingray
On the sandy patch between Ngaio Rock and the Natural Bridge, longtailed stingrays sleep after a night's loveplay. We have always wondered whether one could play with these animals, like holding one by its tail and 'riding its tail' by steering it. The crucial bit comes in two steps: first you must approach without the stingray scurrying away. Instilling trust is a slow process that can easily go too fast, resulting in flight. We had seven stingrays here, so perhaps one would be brave and willing.
The second step is that you must somehow convey a sense of playfulness, touching without meaning harm. To do this, you must not be overbearing, but touch a little bit, then retreat, come back and do it again, much the way a cat would do to another cat - teasing. After five failures, the third ray made a bold move and returned after his flight. A little male, he placed himself right between us, me with the camera and Bruce as actor. Bruce touched it here and there, and lo - the ray touched back. Bruce could slide his hand and arm underneath and lift the ray up. From here it was so easy. He loosely held the ray by its tail, and both swam through the Labrid Channel, while the cameraman could hardly keep up with them. Then I tapped Bruce on the shoulder to let go. He thought I was a spoilsport at the time. But the ray turned back and came for more. It then gradually led us the other way to beyond diving depth and we had to let it go for an unplanned hasty ascent.

I have done this once more since, on a lonely dive without bystanders and cameras. What an experience. To imagine a totally wild animal, very much smaller than me, having enough sense to understand what play is, and then enough courage to give it a go!
 
 
Feeding the stingrays in the Garden of Eden, Mokohinau
A German visitor once wanted to swim with dolphins - no problem. On average, one encounters a pod once every 15-20 nautical miles, so we set out on a tour from Leigh via Kawau, past Little Barrier, skirting Great Barrier and ending up at the Mokohinaus. No dolphins in a hundred nautical miles!
We ended up diving and decompressing in the Garden of Eden, a sheltered cove at the Mokohinau Islands, Burgess Island. It is a wonderful place that gave me many memorable encounters. While snorkelling, I discovered two big short-tailed stingrays, which was not anything spectacular. But back in the boat, my visitor asked whether I had seen anything special. "No, just two stingrays". He almost exploded: "Wass, zwei Roggen?". Apparently these animals have elsewhere quite some reputation. Suddenly his lack of enthusiasm turned into a stampede to get back in the water.

And yes, the Roggen were still there. I noticed that they were looking for something, and then that a yacht was filleting its snapper catch above, the carcass frames raining down. But the rays were seeking by smell rather than by sight. So I took a couple of carcasses and held one up. After three overflights, one ray got the message and took the frame from my hand, ever so gently. Rather than swallowing it as other fish would, its jaws crunched the skeleton like a mulcher would. All the while the ray fluttered around. Once it had completely crunched the meal, it came back for more. In the meantime, the second ray had learnt the routine. My German friend was over the moon, and as he had a video camera, returned home very satisfied. Sorry for the lack of dolphins.

For myself, it was a lesson in how quick completely wild animals can overcome their fears, and then learn something they have never done before in their lives. It taught me never to underestimate stingrays. It was also the beginning of my suspicion that there is something entirely wrong with the sea. For where have all those dolphins gone?
 
 
The spearo attack
After the Goat Island marine reserve was opened, researchers often took their raw material from the reserve, and if this was fish, it needed to be speared selectively (The Department of Conservation did not exist back then). One young scientist was particularly good at that, and often did the work for others.
Now you must remember that the act of spearfishing is quite demanding, and that it is quite an honour to be good at it. In those days, things were done rather pioneeringly, and the spearfisher (spearo) stored the speared fish on a ring attached to his weight belt. We know that this is not a good idea, because the bleeding fish can attract larger fish, like sharks. So a freediving spearo attaches the ring to a float, trailing it some 40 metres behind (this is the depth he can go to). But what do you do when you are spearing for science on a SCUBA lung? You hang the fish off your belt, of course!

So this scienctific-spearo had been sniffed by a large stingray, and as he was surfacing, suddenly the whole world went dark as this stingray wrapped himself around the diver with its large wings, and would not let go. The story is that the spearo peed in his pants, because he was unable to move his hands and could not reach for his knife. Several frightening minutes passed until finally the ray let go. Fortunately this spearo was very experienced and did not panic. And the fish? The ray took the lot!
 


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