Sunday, 21 October 2007

The Shark Highway

This is the inner edge of the barrier reef, which protects the lagoon from the surging ocean. Within it, the lagoon is nearly a kilometer wide, and rarely more than two meters deep. It has many special places, micro habitats, used by animals for different purposes--deep, barren regions where sharks go to rest, shallow areas of thick coral where the babies seek refuge, places where the currents balance creating ideal conditions for spawning fish, places of strong and weak current, favoured by different species, and many more. This channel within the shelf of the reef itself, is used as a highway by sharks on the move.

The Lagoon

This is the view in the other direction, the lagoon where my sharks live. With the sky above, and the earth below, this thin skin of water holds a drama of life I have found nowhere else. Here follows photos of some of the other inhabitants of this magic garden, which forms the setting of my shark stories.

Stone Fish

These three partly camouflaged stone fish represent the least of the reasons NOT to walk in sea water. If stepped on, their spines inject a poison that causes vomiting and possibly heart attacks almost immediately, along with pain so severe it makes it hard to think about what one should do. Walking on the sea floor, even in shallow waters, crushes and hurts animals, large, and small, with every step, without the person even being aware of it. Its best to put on mask and fins where the waves lap upon the beach, and float away through the inches-deep water looking, and not touching, after that.

Visible Stone Fish

These stone fish had just moved so it was possible to see them. The first photo above was taken half an hour later, when their camoflaging process had begun. While they appear among the ugliest of fish, strangely, they are closely related to the lion fish, the most beautiful one, though its poison is more fatal.

Saturday, 20 October 2007

The Fish Who Looks Like a Flower

Amoung the most beautiful of coral fish is the lion fish, related to the stone fish pictured above. It is said to have developed its frilly beauty to impress its food, which consists of crustaceans. I often wonder what that tells us about crustaceans. Its spines, like the stone fish, bear a poison similar to that of the cobra.

Spotted Puffer Fish

Yellow Puffer FIsh

Butterfly

Coral Fish

The intricate coral is home to a multitude. Here a chichlid family shelters within its labyrinths.

Living Waters


Any view in any direction reveals a myriad of life forms, so varied in size, colour, and appearance, that even the water seems to live.

The Sting Ray

Sting rays roam the lagoon, poking about in the sand for food, which they locate using their electric sense. Thus they can often be found by the clouds of sand they raise. These creatures present an awesome spectacle of beauty and grace when they fly, their meters-long tail held elegantly at an angle behind them.

The Eagle Ray

Rays are sharks with wings. The eagle or leopard ray also dwells in the lagoon where my blackfin sharks live.

The Coral Garden

The lagoon where my sharks live is a coral garden of supernatural beauty. This coral formation is an example of the marvels to be found while roaming there.

Tuesday, 2 October 2007

Shark Attack Mania


Shark attack mania is a major obstacle to shark conservation, and seems to be quite obsessive to some, though baseless, considering the facts.
When I first came to Polynesia, twelve years ago, my gardener, Katoa, was my only source of information about the startling shark encounters I experienced when out in the lagoon. He was the only English speaker I knew, having fled the Cook Islands when they became independent and married a Tahitian so he could stay here. So all his life he had fished in traditional ways off the islands of the South Pacific. The question of what to do about sharks was an important one for me, since sometimes they appeared very close and circled me when I was alone a kilometer from land, and all I knew about them was what I had learned from watching "Jaws." I would watch their smug little faces as they turned around me and on the first occasion, felt actually disappointed by the lack of interest the fish displayed in me.
Once Katoa spoke of being especially harassed by sharks while trying to take possession of a fish he had speared. (He was unwilling to give his fishes away, preferring to defend them and take them home to his family). "Why didn't you just hold the fish above the surface and kick the shark?" I asked, having heard that was the best move to make, since it was the fish the shark wanted. He hooted at that, and told me that when his brother-in-law had tried it, the shark had bitten off his fin. "I told him," he said, "You were just lucky that the shark didn't bite your foot off!"
There was a tiny pass, a one foot deep depression, in the reef straight out from where I lived then, and when it was very calm, I used to slide through with the departing surge, and go exploring on the outer slope of the barrier reef. Katoa warned me that there were white tipped oceanic sharks out there, and to be on the look-out for them. He often saw them and drove them away by splashing the surface in front of their noses when they became a nuisance while he was fishing. The move worked much better with them than with black finned reef sharks, he told me, who just circled around and came back. They were the worst pests, he said.
"But those are the ones I see the most," I told him. "Never mind," he reassured me. "If one bites you, just scream and it will let go.
But this is the point: he was seeing oceanic white tipped sharks commonly. Now, they are gone. I wish I had made more of an effort to see them too.
As for the black finned reef sharks, no matter what happened, no one ever did bite me. Wanting them to accept me as companions in my efforts to know them as individuals and animals, I took them food from time to time, in between my excursions to swim with them. My favourite, Martha, would take a scrap the moment it left my hand. She was always in the right place at the right time, without ever accelerating. As an older female, she was about one and three quarter meters in length, and a heavy, powerful shark. The females are larger than the males, who are between a meter, and one and a quarter meters in length.
Martha would go to sniff my boat, and if she detected food in it, she would swim up to my face, over and over, and not leave me alone until I gave it to her. No matter where she was in the vicinity, when I turned towards my boat, she zoomed into place at my elbow to accompany me. I would take the little plastic bag and float the fish scraps out of it as the water filled with blood and fluids. She would coil up past my face, taking the few pieces one by one, paying no attention to the plastic, or the movements of my hands.
Once when I had been given a large load of scraps by a fish store, I was pushing it out of the boat and into the water, finning hard in order to hold myself as high above the surface as I could. And I kicked her, hard, in the side. Horrified, and sure she would turn and bite, I looked underwater to scrutinize the situation. A shark was a couple of inches under my mask, and several others were brushing by me; the water was solid with sharks, but in a moment I was able to make her out, showing no reaction at all to the kick, gliding downward to choose something to eat. (Martha was always a fussy eater, often picking things up and dropping them, leaving not a mark upon the scrap to show where her teeth had held it.)
There was another individual who spent only December to April in my area. (Each female has a different schedule--some are home-bodies, others are elsewhere half the time). I named her Carrelina for a square protrusion on her dorsal fin. She was immature when she first appeared one evening, poking around in the coral. She did the same thing the following three evenings, always at the same place and time, and after that she was consistently waiting with the rest of the sharks when I arrived. (They recognized the sound of my approaching kayak).
Each year, Carrelina became bolder. When I slid into the water, if I didn't move, and just watched them, the sharks I knew very well swam up to my nose one after another, turning away at the last moment, their way of greeting me. Carrelina joined them, but being young she moved very fast. Off and on for the entire hour or so I spent, until darkness veiled the sharks from my sight, every now and again she zoomed up to my face, then startled me by shooting over my shoulder from behind, only to turn like lightning and spend the next several minutes orbiting my head. No effort to dissuade her such slapping the surface of the water in front of her nose, or using the kayak as a barrier and banging on it had any effect. Day after day, week after week, during the four month period of her yearly visitations, she came zooming in at lightspeed, nearly every time I went to the lagoon. Of six hundred sharks I met, only Carrelina behaved in such an amazing fashion. Time after time I felt forced to lay my hand upon her head and turn her--and under my hand how vital she felt, how swiftly she turned. I was always ready to stiffen my arm to ensure that she did not ram me, to guide her around me, but she never tried. Still, she kept me on the alert. Each year her comportment was unchanged. She had no trouble remembering me, the situation, and my routine, year after year, though after she matured, mercifully she moved more slowly.
A famous elasmobranchologist wrote a paper specifically to try to prove that this species of shark is dangerous. He cited examples of sharks behaving as mine did, swimming up to him and turning away at the last minute, claiming that the shark would certainly have bitten had it not been slashed with a machete, or blown up with a power head before it was able to do so. He reported each close approach, which is usually due to curiosity, as a shark attack!
The only actual attacks, that is, bites, he could cite were ones that occurred when people were walking in shallow waters, and the sharks nipped them, apparently attracted by the splashing and mistaking the feet for flipping fish. And those were at Caroline Atoll. As it happens, my friend lived for two years on this uninhabited atoll, and wrote a book about his experiences. (Together Alone, by Ron Falconer) He and his family were used to the sharks' behaviour, following each foot with--I forget the expression he used--something like "excited attention" but he did not consider that the sharks were attacking, just attracted to the splashing--an honest rather than a biased assessment. His children and dog used to played with the sharks, with no harm coming to anyone. They considered them another part of the environment. (Its an excellent book and stunning story--you can get it from Amazon.com.)
The above mentioned elasmobranchologist who sought to prove the black finned reef shark dangerous, reveals his bias by stating in his paper that he was frightened by a member of this species only two feet in length (!!!) who appeared in the area where he was collecting fishes with rotenone. He actually became so frightened that he terminated his activity!
In his assessment later for his paper, the presence of the poison in the water and its possible effect on the shark was not taken into consideration. In another case in which a shark had frantically fought in shallow water while some jerk hacked him up with a machete, the fact that the shark was being cut up alive was not taken into consideration. The mortally wounded shark's behaviour was considered a 'shark attack.' Biased attitudes against sharks, even in science, have probably often resulted in poor observations, false assumptions, and slanted reporting. Then they were accepted as truth. I found the whole thing unbelievable--how such a lot of rot could have been accepted for publishing in a peer reviewed journal is beyond belief.
For a long time I believed that one day I would be accidentally bitten, but it never happened, no matter what went wrong. There was one time when the wind had risen so much during the half hour it took me to paddle out to the site, that I barely had the precariously balanced kayak under control. Instead of undulating languidly behind the boat as she usually did, Madonna, my shark one--she was still alive then, though later finned-- was swimming beneath it like a remora, and countless excited sharks were strung out along the surface behind me, following like children after the pied piper.
The fish shop had cleaned out its freezer, which was the only reason I was out there with this load of stuff; they had packed the scraps in sacks, and due to the wind, I had carefully strapped them on, feeling very conscientious!
But when I slid over the side, planning to tow the boat to the right place, it overturned, due to the high center of gravity. I had to locate my camera and some other things before righting the kayak, with white-caps washing over me and the tossing water opaque with blood and sharks. With the water-filled sacks strapped to it, it was quite impossible to get the heavy diving kayak upright again, so I had to reach under and feel my way to release the straps holding them, one by one.
When they finally fell free, I flipped the kayak upright, and moved into clear water to survey the situation. Greenish clouds of blood hung in the coral, obscuring the view, and through them flew the sharks, eerily emerging and disappearing. Avoiding the blood-scented water, I carried the bags of food one at a time to the sandy circle of the feeding site to dump them out, and once they were in the proper place, the sharks began to feed. No sack had been mauled; they had simply waited for me to put the food in place as usual, despite their evident excitement. Proof of this is offered by the fact that the scraps that had fallen free under the boat when it had overturned were left untouched. It was a remarkable example of how they expected and followed my routine, because once the scraps were in the site as usual, they all behaved as if they were starving to death.
When I first searched this species on Internet, the only references I could find for them were headed "shark attack!" I thought I had made a mistake until I had repeated the search using Carcharhinus melanopterus and came up with the same thing. I wrote to one of the sources, a well known university, to suggest that 14 bites in 500 years by the species is a negligible quantity, and should not be put forward so dramatically, particularly since there was practically no other information about the species. I got no reply, but a couple of years later the website was changed, suggesting that they were aware that since they were supposed to be scientific, maybe they should emphasize their shark attack mania less.
In intimate contact with most species, one is usually eventually bitten, whether it is accidentally by one's dog while playing, or intentionally by an irritated parrot, mouse, skunk, fish or chicken. These blackfinned reef sharks represent the only species I've been in intimate contact with that has not bitten me under any circumstances. Eventually I had to conclude that the strong belief that sharks are dangerous and will bite at any provocation fails to conform with reality, and that this species is inoffensive, and probably has an instinctive inhibition against biting companions, or other large animals.
It was one reason they became my favourites, of all the wild animals I have known: not only did they accept me amoung them, but never did they betray my trust and hurt me.
Ila France Porcher © 2007

Shark attack mania is a major obstacle to shark conservation. This widespread attitude seems quite obsessive to some, though baseless, considering the facts.

Friday, 14 September 2007

Lemon Entrees


So much shark behaviour seems to depend on whether we can see them or not, my main example of that being the time my step-son climbed upon a coral, and instantly the blackfin swimming with us went to him and sniffed his legs, quite aware, it seemed, that having his head above the water he could not see her. This came to mind again last night when I was drifting at dusk sketching the fin of an unknown juvenile blackfin who was roaming nearby. A movement off to the side caught my attention and I saw a good sized lemon shark approaching, already only a few feet away. They always look incongruous coming through the narrow coral canyons, seeming as big as a baby whale, though they are really smaller than that. Not wanting to startle him, I waited, perfectly still, for him to see me. He had a white spot on the tip of his nose, and that dazzling lemon shark smile.

Once my husband and I decided to celebrate Christmas by going to the end of Tahiti. The landscape resembled gently rolling hills covered with sage—the sage being the coral--always sloping downwards ever more steeply, into deepening gloom. Past 120 feet, huge dark purple roses bloomed around us, and the valleys deepened into gulches falling away. The light dimmed as we drifted downwards and finally we could see below that mysterious twilit place, the end of Tahiti. There the drop-off fell straight to the ocean floor, into the utter blackness of the abyss. We were at 200 feet and I was in a dream, more narcked than I had ever been, when a lemon shark came slowly, steadily, almost vertically, up out of the dark. So alien, the beauty; it might just as well have been another world. It saw us and turned towards us, the effect of its relentless oncoming heightened by the movement, back and forth, back and forth, of it's head with open mouth. The grotesque smile was hypnotic, and I saw with wonder that it had visited a joke shop and replaced its normal teeth with two inch spikes just to impress us. I waited for it to turn, actually physically preparing for a fight as I reflected on the reasons it might have for that open mouth. About eight feet away, the shark turned, and just as slowly disappeared into the gloom. My husband took my hand and we began swimming back up towards the light, me looking back often to the mystical place where the island ended.

So with dentition like that, it amazed me again that this lemon shark last night paused and turned away the moment he saw me, a small spindly creature under the surface. They're so shy! His path took him within inches of the little juvenile and neither shark reacted to the close proximity of the other. I went behind a dead coral formation out of the way, hoping he might come back. After a few minutes the slow moving behemoth appeared briefly just within visual range, then disappeared again. This was no accident; he came to look. I waited for awhile, occasionally checking behind me, because often the next thing they will do is come from behind to see. But it was getting dark fast, and I wanted to go. Becoming impatient, I went to my boat and was putting my camera and slate inside when I remembered that its just when my patience comes to its end that the animal often comes, their patience lasting just that little bit longer. So I swam back to my place at the coral, and as I did so, the lemon shark passed me coming from behind.

On another occasion, a lemon shark came with my sharks when I had brought them some food. I didn't feel very comfortable with him there, particularly since the current was so bad I could scarcely swim against it, which put me at a disadvantage, so instead of swimming around I stayed at my boat. Nevertheless, I threw in some tuna heads for him that I had brought for the nurse sharks, then wondered at my sanity when they landed so close to the boat that I felt to retreat up the anchor rope. The lemon shark came and went repeatedly, to my increasing irritation because some of my favourite sharks were just down-current and I wanted to go and see them. So, when he had not appeared for awhile, I let go of the boat and drifted down-current. The lemon shark came immediately, barely discernible through the cloudy light, and he went straight to my boat which he circled around for a time before disappearing again. He was very well aware of what I was doing, just as I had been keeping track of him. (Sharks usually keep watch over suspicious situations from beyond visual range, and that is why often they just appear in the distance for a moment to take a look, then disappear behind their curtain of blue). Later I saw this comparatively huge shark, nine or ten feet long and very stout, nosing slowly along the body of a tiny nurse shark, the size and colour of a human baby, who was munching on a bone. The lack of aggression towards the tiny creature that he could have inhaled whole had he wished, was striking.

Sharks often follow objects of their interest out of sight. To learn who is following you, stop and drift slowly backwards. And there they are, the sneaky things, caught in the act!

There was another occasion, again when it was nearly dark, that a lemon shark came sweeping into my fish party at high speed. There were several sharks over six feet there already, and a couple of about eight feet. I was feeding the fish, and a tiny brightly coloured eel kept waving the front half of his body out of his hole near my right hand. So now and again I tried to waft a bit of food to him. The multispecies cloud of fish agitating in front of me were so thick that I really couldn't see beyond them. I was running on instinct, trying to make sure that each fish got something: a bite for the butterfly fish looking into my mask, a scattering of crumbs for the needlefish at the surface, a bit for the rock cod waiting on my dead coral hold-fast, a handful for the squirrel fishes in the hole to my left, some bigger pieces for the groupers, and something for the five foot moray eel whose head was swaying just below my left elbow. And all the while, whenever I wasn't looking, the tiny eel would touch my hands with the softest, most delicate touches. Suddenly I felt that there was too much agitation in the site: two of the big sharks were moving too fast. So I dropped the tuna head I was using to feed the fish and drifted leftwards just as the lemon shark swept into the circle. Everyone present shot outwards from the centre, an effect called a flash expansion, used at times by fish as a protective measure. The visual effect was incredible—hundreds upon hundreds of jewel-coloured fish shooting outwards in a sunburst pattern along with sharks of all sizes moving at lightspeed. The lemon shark zoomed straight to the tuna head I had dropped and went nearly vertical, (as much as a three meter shark who is fatter than a horse can in two meters of water), with a great deal of tumult, as he tried to extricate it from under the coral. He failed, and came along behind the coral wall I had been using as a hold-fast. Horrified at this turn of events, since I had heard that lemon sharks can become irrationally angry, and this shark was already in a huff of some sort, (plus it was nearly dark), I remembered I had promised myself a photo of the next lemon shark, and readied my camera, an underwater throwaway, bought just for such unexpected opportunities since my usual one was being fixed.

Amazingly, the huge shark still had not seen me, and as he approached, I saw in awe that his head was covered with long, deep, criss crossing scars! He was just about underneath me when I took the picture, and he reacted so fast when I moved my finger to press the button, that the photo shows him already turned. How he got turned around in that narrow space is hard to picture, but he accelerated away and vanished. Shaking with terror, I threw my stuff into the boat and nearly drowned trying to get my anchor out from under the coral where it had become lodged, so frantic was I to get out of the water before he came back.

Once in the boat, I drifted, watching, over the glassy waters, rainbow colours melting together beneath the afterglow of the western sky. But I did not see the lemon shark, or any shark, reappear in those twilight waters.

Ila France Porcher

Thursday, 13 September 2007

Sharks: Wolves of the Sea

When I came to Polynesia, I was familiar with Canadian wild animals and had no idea what to expect when I began to meet sharks while exploring the lagoon. After a series of odd experiences with them I set out to find out what they were really like as animals and individuals. The species I concentrated on was Carcharhinus melanopterus, the reef blackfin shark.

To see what each one was doing from day to day, I had to be able to recognize them. So I drew their dorsal fins on each side, then copied them into a book, along with a description and any other details. I soon had so many that I had to give them names just to be able to remember them all. My notes grew to hundreds of pages and dozens of tables, and by now I have identified more than six hundred sharks, and could recognize half that many on sight before a large fraction of them were finned (starting on my study group in 2003—see 'In Memory of Madonna'). I spent as much time as I could with them, bringing them treats now and then as a gesture of benevolence.

Beneath the glimmering lagoon surface, in a thin skin of water just one and a half to two meters deep, exists an ecosystem of extraordinary complexity and vividness. Its always impressive: the sky above, the earth below, the sun slanting through the gently moving surface gilding the turquoise waters and the surreal landscape with golden light, and in just this tiny layer, so much life in all directions, it takes your breath away. Even the water seems alive. In that split second it takes to slip underwater, I go from being alone in the wind, to being surrounded by two or three dozen animals the same size as me, all approaching. There is always something surreal about it, the alien beauty, and the silence in which they move. One by one, those who know me well, swim up to my face, turning away at the last minute, if I just stay still, watching them.


For a long time this gesture was a mystery to me, and I finally decided it was an expression of excited recognition, like the way dogs will joyfully run to you when you arrive home.


That they always approach my face, indicates their recognition of the frontal view. On the other hand, strange sharks will come from behind to take a closer look without being seen, or pass close by when I'm looking the other way. Often sharks will immediately react when they become aware that a person cannot see them, for example when one looks above the surface. Sharks appear to use the limits of visibility to remain out of sight when it suits them, coming just close enough to have a look once in awhile, and keeping track of the object of their interest by using their other senses (hearing and detection of vibrations in the water-medium). Thus they appear to be aware of being present and viewable. Similar behaviour has been considered in bears as an indication of self awareness (Donald R. Griffin 'Beyond Cognition to Consciousness' 2001). A variety of behaviours indicating thinking in sharks are described in my accounts of specific individuals, soon to be put on line on my planned website, which constitute some of the first observations of cognition in sharks.


In time I became familiar with their daily life habits, social lives, and reproductive cycle—the article reproduced on this site 'On the gestation period of the blackfin reef shark, Carcharhinus melanopterus, in waters off French Polynesia' was published in the journal Marine Biology.


Most males, who are smaller than the females, live on the outer slope of the barrier reef; it is the males you mostly see on shark dives. The lagoon is the usual domain of the females and juveniles, and so it was those with whom I became most familiar. Each shark has a preferred area, called the home range, and these ranges overlap. Sharks living in the same region know each other as individuals, and have companions they often go with when they travel elsewhere. This indicates that sharks recognize each other as individuals, and because they appreciate a companion, it was easier, I think, for me to be accepted by them as a companion.


On the few occasions when I came with another person, they responded by vanishing behind their curtain of blue, sometimes after coming quickly over to verify my identity. They could tell the difference between me and another human; in other words, they recognized me as an individual too. Besides involving learning and memory, such behaviour showed their awareness of changes in the routine or their environment, and their ability to make quick decisions.


One of the very large and apparently quite old females I met was very dark, with a pure white marking symmetrically placed on each side of her head. It looked as if someone had stuck two large snowflakes on her. Arriving always at dusk, she was a dramatic sight with the twin white points glowing bright. I called her Kimberley. She remained in the area for nearly a month, and before she left, I saw another very similar visitor. Not only was the patterning of their colour lines and dorsal fins alike, but this shark, too, had pale markings placed precisely the same way on her head. She also arrived as night fell, and I called her Twilight. Since none of the other sharks had this type of white marking, I speculated that the two sharks were sisters. It was months before either of them returned to the area, but there came an evening when the twin snowflakes approached through the gloom. Kimberley glided in, and the following week, I saw Twilight.


For three years I watched the two come and go every few months, sometimes together. Was it chance? Or was there an association between them? Finally, when Kimberley appeared again after months of absence, at nightfall, I went looking for Twilight and actually found her, following about a minute behind Kimberley. She passed me, and just then Kimberley appeared equally distant on my other side. The two sharks were arcing towards each other, as though following the same circle. They met in front of me, passing so closely they may have brushed each other. But though I watched intently, I discerned no sign pass between them. Maybe just the close pass was the important thing, each shark reaffirming 'we are here.' Twilight languidly cruised back and forth in a figure eight pattern, strangely not minding me staying with her. Time after time she caught up to another female shark who was already present, apparently intercepting and pursuing her trail of scent. Then the two would swim together briefly, usually, before moving on and joining another shark.


Kimberley and Twilight arrived together at dusk each time I saw them for the following month, reinforcing my theory that they were associated, and maybe sisters. They continued their sporadic visits until shark finning began here, whereon Kimberley immediately disappeared, and Twilight held out for awhile, before she too vanished. Nearly all of my beloved females were slaughtered within a few months when the killers from Singapore arrived here, and the government pondered over whether or not to let them devastate the country's sharks.


Clementine and Odyssey were large, elderly females. They visited the study area together in the dark of the moon at the end of April four years in a row, and at no other time. Cheyenne, who was in about the same age-group, accompanied them the two last years, but after the initial visit she returned alone every few months. This is one of the more exceptional examples of sharks following a surprisingly precise schedule as well as traveling with favored companions.


Companions apparently move in loose contact, regularly meeting and moving on for awhile together, either side by side or nose to tail, but most of the time out of visual range of each other. They make wide circles forming enormous figure eights or cloverleafs, ideal for intercepting scent trails. Odours that interest them are from other sharks as well as possible food sources it seems, and thus, as well as through their sensitivity to underwater sounds and vibrations, they can remain in loose contact as they travel.


One morning when I went outside at 5:00 a. m., a single white feather fell from the empty sky to lie upon the surface of the lagoon, and as if in a spell, two shark pups appeared. Apparently just out of the nearby nursery, they were scouting the area, their circles and turns creating a mesmerizing ballet, full of grace. Sometimes they swam separately, sometimes they followed each other; sometimes they swam after each other in a perfect circle, each with its nose six inches from the tail of the other. The school of baby tangs that lived in the shallows formed a little yellow cloud, pointing towards them as they passed. A mynah bird swooped down to look. Sometimes they followed other fish, sometimes other fish followed them. The rhythmic side to side motion, like a heartbeat, that typifies this most graceful creature, felt like a beat in their music. Though I had formed a theory about being able to estimate the size of fish from the ripples generated on the surface, the passage of these little sharks showed not a sign upon the glassy surface. At 7:20 the neighbours started trying to shoot them, and bragged all weekend of their fruitless efforts, as though they had taken on visiting monsters.


Presumably the babies got to know each other in the nursery, where they were born alive in shallow, protected waters, and may even have been siblings. Such long term companionships as I witnessed in adults, could conceivably have begun just like this.


After years of watching sharks in different situations and interacting with them, I think that their type of mentality urges them to get one step ahead of the object of their attention, clearly an advantage to predators who run down fish for a living.


No matter what happened, I was never bitten by any shark, though in intimate contact with most species, one is usually eventually bitten, whether it is accidentally by one's dog, or intentionally by an irritated parrot, mouse, or skunk. Sharks were the only type of animal I had intimate contact with who never bit me, and I came to believe that this species, at least, has a built in inhibition against biting companions.


It was one reason they became the favoured ones, of all the wild animals I have known. Never did they betray my trust and hurt me. No matter what happened or went wrong, time after time.


I hope my accounts will contribute to appreciation of sharks as the intelligent animals they are, counter shark attack mania, and encourage their conservation.


Ila France Porcher © 2006

Sunday, 19 August 2007

On the gestation period of the blackfin reef shark, Carcharhinus melanopterus in waters off Moorea, French Polynesia

Originally published in the Journal "Marine Biology" at:


Abstract
Underwater visual and photographic observations, over a four year period, monitored the presence of mating wounds on female Carcharhinus melanopterus. Mating begins in November and continues until the end of March as each female follows her own temporal cycle. Correspondingly, parturition begins in September and continues until January. Each female again mates 1.5 to 2.5 months after parturition, thus completing an annual reproductive cycle. The gestation period is 286 to 305 days, with slight individual differences. All resident sharks under observation followed this pattern. Evidence of reproductive events presented by transient females conformed with the pattern of the residents.


Introduction
The few studies postulating a gestation period for the reef blackfin shark Carcharhinus melanopterus have varied greatly in their conclusions. Based on an examination of embryo development, Melouk (1957) claimed a 16 month gestation for the species. Based on measurements of embryos in pregnant females and supported by testes-mass to body-mass calculations, Stevens (1984) concluded that the gestation period was 10 to 11 months. Lyle (1987) examined the reproductive organs of reef blackfins caught in nets, and concluded that their gestation period was 8 to 9 months. Concluding that an entirely new method was needed to resolve these conflicting findings, I used direct observations of the sharks, and found values close to those proposed by Stevens (1984).
Mating wounds have been commonly found on females of many species of elasmobranchs (Kajiura, et al 1999, Pratt 1979, Jensen 2002). The male reportedly grasps the female by her pectoral fin with his mouth to stabilize the pair, while mating (Tricas and LeFeuvre 1985, Jensen 2002). These wounds infer mating activity in the observed females and wounding can be extensive on the pectoral fins as well as along the posterior, lateral, dorsal or ventral body surfaces. Kajiura, et al (1999), wrote: “Fresh wounds are formed during periods of active courtship and copulation, and can thus serve as indicators of mating activity even when it is not directly observed.” Jensen also noted that fresh bites observed on a female shark “ ...may coincide with insemination and ovulation, marking the approximate beginning of the gestation period.”
The pregnancy of each resident shark was monitored. Parturition was signalled by the reappearance of the newly slender female.

Method
The concept that individuals can be distinguished by their appearance underlies photo-identification techniques. These have become standard practice in the study of marine mammals (Hammond 1986; Defran et al. 1990; Würsig and Jefferson 1990) and have been used effectively on white sharks (Carcharodon carcharias) (Anderson and Goldman 1997). Working underwater, I complemented photo-identification techniques by accurately drawing both sides of the dorsal fin and recording the length, color, gender, behaviour, scars, marks, and more subtle distinguishing features of each shark ranging the western part of the Vaihapu region (Galzin and Pointer 1985) off Moorea Island. The appearance of each individual on both sides was recorded to avoid error in future sightings wherein only one side might be visible. On encounters, sharks have a tendency to fix one eye on the observer, resulting in circling. Efforts to see the shark's other side are countered by the shark, who appears reluctant to lose this visual contact. The drawings, with written descriptions, served as well as photographs, and resulted in the identification of over 450 individuals.
Observations over a period of 4 years were carried out 2 to 3 times weekly, conditions permitting, and more often when events demanded it. Presence, condition, and signs of reproduction were recorded for each individual. The residents were identified and became familiar to me during the first 3 months; the total number of adult females observed was 172.

Results


Structure of wounds

Mating wounds in C. melanopterus consisted mostly of punctures and cuts of about 2 to 3 cm in length. A few were much longer and gaped open, revealing the subdermal layer. They appeared as sets of parallel and single cuts, angling posteriorly, in which no flesh was removed, and apparently inflicted by the upper jaw of the male during mating (Pratt 1979). One or both pectoral fins were usually sliced, sometimes to the leading edge, in several places (Tricas and Le Feuvre 1985; Jensen 2002). Dermal tissue was removed between bite-marks wherever they were close together. The deepest, gaping cuts occurred below the lower colour-line (Figs. 1, 2) where the skin might be easier to pierce and slice. These wounds typically covered the females with a fine latticework in a long teardrop shape on each side, beginning in front of the gills, widening to the dorsal fin, extending below the lower colour-line, and tapering off, at or before the second dorsal fin. When fresh, the wounds looked clear-cut, and light-red, vascularised tissue was visible. Then the edges softened, and the wounds paled. Within 4 or 5 days the cuts were edged in black, and began to close. Klimley and Nelson (1981) also reported that abrasions on female scalloped hammerhead sharks (Sphyrna lewini) became black patches during healing. The shallower bites healed and disappeared in 10 days, leaving a wider spaced network of black lines. Only the deepest cuts still gaped. The pectoral fins were almost healed in 10 days with 1 or 2 wounds still presenting an open V-shape less than 2 cm long on their trailing edges. These had closed 2 to 3 weeks after mating. The mating wounds had completely healed in 4 to 6 weeks; the gaping wounds below the colour-line remained visible longest, as dark lines. The skin was left mottled with paler marks which slowly normalized during the following weeks. For about 2 months, the shark's overall colour was paler than normal.
Occasionally, a female showed cuts in only a few places. Appearing in parallel lines, these again, suggested bites from the upper jaw of the male (Pratt 1979). Such cuts were usually on the dorsal surface or flanks, posterior to the first dorsal fin. However the full set of lacerations as described above occurred only once per season per individual.
Females appeared with mating wounds one by one throughout the warm season, from November to March. The sole exception was an individual that mated within the first 3 days of April in one year. No similar bites were seen on males, though rarely one appeared with a bite-mark. Occasionally, a male presented a slash-wound, usually vertical on his side near the gills, from near the dorsal ridge to the curve of the ventral surface.

Temporal cycle

The progression of pregnancy was followed after noting mating by an individual. Soon the streamlined shape, typical of the non-pregnant female, became more rounded as her circumference increased. By contrast, males have a less convex profile. Clear, abdominal distention became apparent after 3 or 4 months and was never noted in non-pregnant females; these always maintained a sleek outline. As months passed, both the abdominal swelling and obese appearance, became more prominent (Fig. 1). The slight angle on the dorsal surface, posterior to the head, became more acute. About two weeks before parturition, the lower abdomen near the pelvic fins, began to bulge on each side (Fig. 2), so that viewed from behind, this area acquired a squared shape. When parturition approached, distention there became extreme, creating a gap between the pelvic fins and the body about 3 cm wide at the fins' tips, presumably due to the young moving into position for parturition.

Parturition resulted in a remarkable change in the shark's appearance. She reappeared in her home range looking almost emaciated (Fig. 3), and some individuals, though not all, became strikingly paler. Over the following few weeks, her usual colour and more convex profile were re-established.



Parturition began in September after about 10 months (Fig 4). Each individual mated again after a period of about 40 to 90 days although the usual resting period was 45 to 75 days. Young females appeared to be more erratic in the timing of their cycle from year to year, but the older individuals tended to mate and give birth at approximately the same time, often to the week, year after year. Each shark reproduced annually, as noted by Lyle (1987). Of 13 monitored young female sharks mating for the first time, only 2 became pregnant, while fully mature sharks almost never failed to reproduce successfully each year. The evidence of reproductive events obtained on transient females agreed with observations of the residents.


The upper and lower limits of sample gestation periods in cases where the shark was observed regularly throughout her pregnancy are presented in Fig. 5. These were residents with little tendency to roam, so some could be watched year after year. Other residents left their home ranges for such long periods during the reproductive season that the timing of either mating or parturition could not be accurately determined.
The shallow regions at both ends of the barrier reef bordering the Vaihapu area were used as pupping grounds. Neonates appeared there in general correlation with the timing of noted parturitions, serving as confirming evidence of this facet of the reproductive cycle.





Fig. 5 Sample gestation periods by residents. Certain individuals were monitored year after year, permitting comparison of successive gestation periods. The minimum figure gives the number of days from the first sighting of the shark after mating to the last one before parturition. The maximum figure gives the number of days from the last sighting before mating to the first after parturition. N=27. Averages: Minimum: 286.6 ± 10.7 days; Maximum: 305.1 ± 10.5 days.

Discussion



While a camera or video-camera only records the scene-data frame by frame, the human eye can instantly capture and integrate needed information as it follows the moving image of the shark. By simultaneously recording this information through drawing on a slate, a cognitive process involving visual information extraction, normalization, and solidification is completed, that no machine is yet able to do.
In the time it takes to raise a camera and frame a swiftly passing shark, the animal may well have proceeded far enough that the dorsal fin pattern is no longer visible. There is the possibility that the sudden movement will cause the shark to veer. Often a shark is too far away to capture on film, though the pattern of its dorsal fin is clearly seen. Drawing can extract information from swiftly moving sharks in low light conditions, which are unsuitable for photography. Further, the drawing process etches the appearance of the shark on the mind, facilitating future recognition. Therefore, with my technique, many times the amount of information was obtained, per unit of time, than would have been possible with photo-identification techniques alone.
My results indicate a gestation period of between 286 and 305 days, with minor individual differences, and an annual reproductive cycle for Carcharhinus melanopterus off Moorea Island, which is in the southern hemisphere. Melouk (1957), in his study of embryonic development in this species, found that the reproductive season in the Red Sea, in the northern hemisphere, also takes place during the warm months. His assumption of a 16 month gestation period was given in the Introduction of his paper, but was not substantiated with data to permit the reader to follow his reasoning. It was based on the finding of “...embryos about 2 cm long as well as advanced stages about 40 cm long...” in different individuals in May, then, “ ...older stages measuring about 3 to 4 cm as well as foeti [sic] about 50 cm long...” in June. No data exist for July and only an expectation is offered for August, when neonates were found “ ...commonly round the shores.” Given that he infers that parturition occurs in August, a 16-month gestation-period means that mating occurred in May of the previous year. However, according to his own data, the embryos were already 2 cm long in May. This contradiction is not addressed nor does he mention how long it takes for an embryo to grow to a length of 2 cm, a point mid-way between the stages 6 and 7 described in his paper, when the embryo is already well developed. He states that “ ...mating season starts, as far as it could be ascertained, early in summer...” but, he does not specify the method used to ascertain the start of mating nor when, precisely, early summer occurs in the Red Sea. Since fetuses of 50 or even 40 cm in length, should be close to parturition, one wonders whether parturition might begin earlier than August. This point is not mentioned, nor are sample sizes. The few data in Melouk (1957) are not inconsistent with my observations that some sharks had already undergone parturition and mated again, while others had not. However, his data are inadequate to determine the gestation period.
Stevens (1984) made an extensive tagging study of the sharks at Aldabra Atoll in the Indian Ocean and dissected a number of individual Carcharhinus melanopterus to determine their reproductive cycle. He postulated a gestation period of 10 to 11 months for this species with mating occurring in October and November, and parturition in October, based on measurements of embryos in pregnant females and supported by testes-mass to body-mass calculations. His study suggests that the mating season at Aldabra is restricted to October and November and he found that about half the females became pregnant each year and were in a resting period during the following year. The intense intraspecific and interspecific competition for food, he reported, could be a factor in the alternate-year reproductive cycle occurring there and his results indicate a distinct variation in the reproductive cycle of C. melanopterus between these two distant island-groups, Aldabra Atoll in the Indian Ocean, and French Polynesia in the mid South Pacific Ocean.

Lyle (1987) postulated an eight or nine month gestation period, following examination of the reproductive organs of sharks caught in nets in northern Australia. His data indicate a mating season underway in November to March and trailing off in April. These data correlate with mine. He mentions two individuals with low ovary weights and low ova diameters in February, explaining that the gonads appeared to be in a resting state: “ ...uteri were expanded but ova were small and without yellow yolk typical of the pre-ovulatory condition.” This state could have been found in individuals that had undergone parturition and were not ready to mate again, typical of some individuals at this time of year off Moorea. Lyle (1987) mentions a female with uterine eggs in March, indicating that ovulation extended into that month as well. This is also consistent with my findings. Lyle's conclusion of a relatively short gestation period might have been affected by small sample sizes. He states, “The paucity of material in November-December and the absence of females with mating scars make it difficult to establish the precise timing of the mating season.” Insufficient data (only one female and no males during the important month of December) might have led to an incorrect conclusion, particularly given the variation I observed in the timing of the reproductive cycles of different individuals.
Johnson (1978) stated that two mating seasons had been reported in the Indian Ocean for C. melanopterus: June to July and December to January. He added that in French Polynesia, evidence supports this dual pattern. Since he did not specify what this evidence was, it is not possible to discuss it here, and apparently Johnson did not determine the reproductive cycle in detail. Since the reproductive pattern I observed was clear and precisely repeated year after year, I conclude that there is no biannual reproductive cycle in French Polynesia. A biannual cycle observed in the Indian Ocean might be related to the proximity of the equator, where the warm season might be less distinct. Depending on movement-patterns of the species, regions from both hemispheres could have been the origins of the sharks within the given population, each individual continuing its ancestral cycle in the present-time. Further observations and DNA studies could help reveal such possible influences on variations in the reproductive patterns of this species in different regions.

Acknowledgements
I sincerely thank Arthur. A. Myrberg Jr. for his encouragement, for locating needed references, and reviewing and advising me on the manuscript. Thanks to J. Castro, R. Galzin, L. Paul, and M. Kazmers for providing references. My husband, F. Porcher reviewed and provided helpful suggestions on the manuscript. The Centre de Recherches Insulaires et l'Observatoire de l'Environnement, on Moorea, and the Richard Gump South Pacific Research Station, University of California at Berkeley, on Moorea, permitted me access to their libraries. All observations comply with the laws of French Polynesia.


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