What Are Sharks Aware Of?

More and more divers are meeting sharks for the first time, and wondering, “What do they see when they pass, gazing at us gazing at them?”
Sharks have a very different set of senses than we do, yet the eye-sight of the free swimming species is good, so passing sharks who have approached to look at you, are really seeing you. But you may have the impression that they are using senses other than their eyes most often, and indeed, apart from our shared good eye-sight, it is impossible for us to imagine how sharks experience their liquid realm.
Sound and vibration are very important to them. Sound travels far in water, spreading out in a uniform spherical pattern, and sharks hear well. They are particularly sensitive to low-frequency vibrations, such as those caused by movement in the water, and crashing waves. And they can detect pressure waves with the sense organ called the lateral line.
The lateral line is found in fish, sharks, and some amphibians, and is made up of a series of receptors in a line along the length of the animal. The receptors consist of a sensor within a cupola of jelly, which is directly affected by pressure in the water, just as the hair cells in our inner ears, which keep us balanced, are directly affected by movement. It is thought that the lateral line and the inner ear have a common origin far back in evolutionary time when life was selecting the basics. A complex nervous system analyses the incoming information in each tiny receptor, enabling sharks to perceive events beyond visual range through these pressure vibrations. They are aware of a person or animal moving in the vicinity, while remaining unseen, beyond the blue curtain of the visible range. The view of their environment that sharks gain through this sense, with receptors mounted the length of their bodies, is quite unimaginable for us.
Some of the sharks present at a shark feeding dive may have come to investigate, after hearing the submarine uproar caused by other sharks feeding. On their first approaches into visible range, you will see that these late comers generally pass just barely into view. A few minutes later, they will come again, probably closer.
Then there are the electro-receptive organs, the ampullae of Lorenzini. They detect voltage―electrical potential across a barrier. This is not the same as the ability to detect current flowing through a conductor, such as along a nerve—sharks cannot detect brain waves. But they can hear the beating of your heart, and sense other signals about your subjective state.
The ampullae of Lorenzini can pick up the voltage emitted by working muscle tissue. Sharks easily detect such voltage down to the microvolt range, the range emitted by most sharks’ prey. Since sea water is saltier than blood, the difference in ionic concentration produces an electrical potential between the inside and the outside of fish. The animal’s skin shields most of it, but there are places, such as the gills, that emit a faint electric field that sharks can detect.
It has been calculated that in a perfect ocean, a typical shark could detect a one-and-a-half-volt AA battery from a distance of hundreds of kilometres, but the ocean is full of background noise that limits the range to about a metre. Sharks and rays use their electro-sense to detect living prey at close range. This works even when the prey is hidden in murky water, or when it is buried in sand.
Lastly, a shark can taste and feel its prey with its sensitive mouth, which is the only part of its anatomy designed by nature for contact with the solid environment.
All of these senses are used in different combinations, depending on species and circumstance, just as we at times use hearing more than sight, and at other times are focused on an odour or touch sensation. The more than four hundred seventy species of sharks, diversified across eight orders, inhabit a wide variety of environmental niches, so their senses are adapted accordingly, and doubtless vary widely, just as birds adapted to different habitats are very different.
Sharks are aware of a very different reality than we are, yet underwater they appear as peaceful and very rational animals as they pass, looking at divers looking at them. It is possible that they can sense whether you are stressed or frightened, or completely relaxed, which could indicate to them that you are not in attack mode. Shy sharks will avoid you most when you are purposely finning and looking for them, for example, and if you want one to approach, stay very quiet in the water, and it might come closer for a look.

Extinction Soup

Extinction Soup is the inspired name of a new, dramatic film on the shark finning crisis, which Hawaiian film maker, shark diver, and advocate, Stefanie Brendl is spearheading. Philip Waller is the writer, producer and director, Sidney Sherman is the producer, and Travis Aaron Wade is the co-producer. The film is expected to be released in early 2014. For more information, have a look at their site.
http://www.indiegogo.com/projects/extinction-soup
All support is much appreciated, and there are lots of perks for those who donate something to this important project.
Congratulations Stefanie! Good on you all for creating this fantastic work on behalf of sharks!

Pain in Fish : a review of the evidence

Fisherman James D. Rose claims that fish can't feel pain. He has published a paper stating that the neocortex, the outer folded layer of the brain that is so highly developed in humans, is the seat of all higher mental functions, including consciousness of pain. Therefore, the neurological machinery required to feel pain is missing in a fish, and indeed, is present only in humans and apes. But, in focusing on a comparison of the human brain with the fish brain alone, Rose's article seems biased and anthropocentric.

Rose did not give a reason for his assertion that consciousness depends, alone, on the neocortex. Nor did his argument take into account the straightforward evolution of the vertebrate brain. From fish to man, the brain has the same structures, arranged in the same way, with the exception only of the neocortex, which developed in mammals. Neurological studies have shown that the newly evolved neocortex of mammals took over certain higher functions, which were already present in fish, amphibians, reptiles, and birds. (I. Glynn 1999)

The expansion of the forebrain has occurred many times in different species, including in some fish, whose brain structures would fall into Rose's category. All teleost fishes (bony fishes) have elaborate forebrains (Butler and Hodos 1996) and the degree of forebrain development has been correlated with social behaviour, and communication abilities, which are considered to be integrated with cognition. (Kotrschal et al 1998).

Fish continue to develop neurons throughout their lives, and do so at a faster rate when confronted with a stimulating environment, indicating a link between experience and neural development. For example, the triggerfish, (Balistidae), which have advanced foraging techniques, have a relatively larger telencephalon—the front part of the forebrain—than most other families of fish investigated (Geiger 1956).

It is well established, for example, that birds feel pain, and have advanced cognitive abilities. Some species have better long term memories than humans, and others far exceed us in visual recognition. Yet their little pea-brains lack a neocortex. The miniaturization of the animal did not affect mental capability (Barber 1993). Tests with birds showed that higher mental capabilities could be found in a brain that is wired differently than ours. Dolphins, too, show high cognitive capabilities, but their brains have a different form than primate brains, though both are mammals (Marino 2002). There are people in which the expanded neo-cortex failed to develop, but who have normal psychology and IQ's. (Edelman and Tononi 2000). So even in humans, it seems that the neocortex is not necessary for consciousness.

Other researchers have concluded that the neocortex was not central to consciousness. Donald R. Griffin, (1998) theorized that the expanded human brain had allowed the appearance of a complex subconscious mind. Since consciousness was more likely to have been favoured by evolution due to its value for survival, he considered it more probable that the centralization of the nervous system had resulted in consciousness. No brain is simple, as anyone who has observed the activities of a spider will appreciate.

Laureys et al (2000), and other researchers, found evidence that the thalamocortical system was the essential neurological basis of conscious awareness, and Chapman and Nakamura (1999) concluded that the neural systems involved in the detection of tissue damage, (nociception) and the awareness of the pain, likely evolved as an “interactive dynamic system” with the cognitive processes, in the evolving central nervous system. These findings and others suggested that it is the way the various regions of the brain are integrated, that generates consciousness.

All of this easily available evidence that contradicted Rose's conclusions, was omitted in his article. He seemed to rely on the beliefs of fishermen, that the fish brain was so simple that it was well understood, and that it could not support consciousness. Unfortunately, fishermen had given it so much publicity that people remembered only that science had proven that fish don't feel pain. Some people started claiming that fish were missing part of their brains!

Rose ascribed Pavlovian learning, only, to fish, denying any possibility that consciousness could be involved. Other researchers found evidence that showed otherwise, and denied that learning in fish takes place in the total absence of cognition and consciousness. (Maren 2001, Lovibond and Shanks 2002; Overmier and Hollis, 1990). Chandroo et al (2004), acknowledged that learning processes seen in fish, “may require the formation of declarative memories.” (Declarative memories are memories of facts, which we can call on to use, consciously, at any time). In reviewing the relationship between learning in fish, memories, and conscious cognition, Chandroo et al found that some fish behaviour is better explained within a theoretical framework that includes primary consciousness.

Fishermen will claim that fish don't feel pain, because they have seen sharks continuing to function in spite of terrible wounds. However, this is a common behaviour even in humans. Fear is generated from deep in the brain and will over-ride pain. The effect has an obvious benefit for survival.

Another argument declare that fish cannot feel pain because sometimes a fish will bite a baited hook a second time, after being unhooked and thrown back into the sea. But, while it may be obvious to the fisherman what he is doing, how could it be obvious to the fish? These men assumed that the fish understood much more than it possibly could about its situation. It could have no basis, among its experiences in life, for understanding the fisherman's practice of deception—the possibility of a hook hidden in the bit of food it had found.

It can see no dangerous predator underwater, so how could it imagine that above the surface a man is waiting, hoping to trick and kill it? Even a human walking by the sea pursuing his own affairs, would never suspect that there was a creature waiting for him beneath the surface with a plan to trap and kill him. A fish that had already bitten a bit of food with a hook in it, has no reason to assume that the next piece of food it finds will also hide a hook.

But why ask those whose only interest in fish is to kill them? There are people who have good will towards fish : veterinarians. A bird specialist in Australia, Dr. Pat Macwhirter, wrote to me that she had assisted in surgery on a fish when a fish vet had come to work at her animal hospital. She described the fish being more sensitive than birds to electro-surgery, and said that the anaesthesia had to be deepened. There was no doubt, she told me, that the fish had felt pain.

With their training in healing, and experience with distressed animals, it seems to me that veterinarians are in a much better position than fishermen to judge whether or not an animal is in pain. I too had noted that the sharks who had escaped being landed for finning, as well as female sharks with extensive mating wounds, showed similar signs of pain as other classes of animals. They were less alert, less reactive, and slower moving.

Temple Grandin and Mark Deesing at the American Board of Veterinary Practitioners Symposium of 2002 declared that “the ability of an animal to suffer from pain may be related to the amount of associative neural circuitry linking sub-cortical structures to higher levels of the nervous system.” They considered that one could assume that an animal was in pain if it actively sought pain relief, protected injured parts, became less active when sick or injured, or self administered pain killing drugs, all of which are seen in fish, whose bodies release strong analgesics, which relieve pain.

The work of Dr. Lynne Sneddon, at the University of Edinburgh revealed 58 receptors located on the faces and heads of trout, that responded to harmful stimuli. They resembled those in higher animals, including humans. A detailed map was created of pain receptors in fish's mouths and all over their bodies.

Dr. Sneddon injected the lips of trout with acetic acid, bee venom, or saline solution as a control, and found that those injected with the noxious substances showed symptoms of pain, including an accelerated respiratory rate, rocking back and forth on their pectoral fins, rubbing the affected areas on the substrate, and taking longer to resume feeding than the control group, whose behaviour remained normal. A morphine injection significantly reduced these symptoms. (Sneddon, 2003)

The relief of the fishes’ symptoms by the pain reliever shows the interconnection between the nociceptors, which sense the tissue damage, and the central nervous system. Here was proof that fish are aware of tissue damage as pain.

Other researchers published papers showing that fish vocalize when they feel threatened. I too, have found that when I stroke triggerfish hiding in a cavity in the coral, it squeaks at precisely at the moment of each caress.

Rebecca Dunlop of the Queens University of Belfast, found that fish learn to avoid pain. She said: “Pain avoidance in fish doesn't seem to be a reflex response, rather one that is learned, remembered and is changed according to different circumstances. Therefore, if fish can perceive pain, then angling cannot continue to be considered a non-cruel sport.”

When told of these findings, James Rose replied: “One consequence, at least where I live, is that all the revenues that support research on the habitat of fishes, that monitor the health of the fish populations here—all the biologists who do this work are funded by (fishing) licence revenues. If there was no fishing there would be no one to do their job. That would be a catastrophe. That would be a colossal loss, and believe me, there would be no other funds from other sources to do the same job.” (James D. Rose speaking to science reporter Abbie Thomas, the producer of “All in the Mind,” at ABC)

This seemed a further indication that his paper allegedly proving that fish don't feel pain was politically motivated rather than an honest desire to find out the truth. Note that he had done no study, as Dr. Lynne Sneddon did, to determine whether fish feel pain or not. He had simply declared that a difference between the human brain and the fish brain proved that fish can't feel pain, while ignoring other relevant evidence.

And it can be argued that research by and for sport fishermen is of questionable ultimate value since it focuses only on the target species, to the neglect of the others in the aquatic community, and is conducted in hope of favourable results for a political cause. 

Sneddon's results have been found since by other researchers who have further investigated the best way to relieve pain in fish during surgery. (Harms et al. 2005) Pain relief is now systematically used by veterinarians who perform surgery on fish, in the full belief that they feel pain. It is now believed that the pain system in fish is virtually the same as in mammals.

It is daunting, how many people remain proud of their efforts to outwit fish. They don't see the irony in claiming that fish are too simple to feel pain, while being proud of their ability to outwit them. This appears to be the mindless acceptance of a tradition, resulting from a discovery in the stone age, and, incredibly, still bragged about in the computer age.

References

Alexander RD (1987) The biology of moral systems. Aldine de Gruiter, New York
Aronson LR (1951) Orientation and jumping behavior in the goby fish Bathygobius soporator. Am Mus Novitates 1486
Aronson LR (1956) Further studies on orientation and jumping behaviour in the goby fish Bathygobius soporator. Anat Rec 125:606

Bshary R, Wickler W, Fricke H (2002) Fish cognition: a primate's eye view. Animal Cognition (2002) 5 : 1-13

Colin PL (1972) Daily activity patterns and effects of environmental conditions on the behaviour of the yellowhead jawfish Opistognathus aurifrons, with notes on its ecology. Zoologica 57:137-169
Colin PL (1973) Burrowing behaviour of the yellowhead jawfish, Opistognathus aurifrons. Copeia 1973:84-90
Barber TX (1993) The Human Nature of Birds. Bookman Press, Melbourne

Clutten-Brock TH, Parker GA (1995) Punishment in animal societies. Nature 373:209-215

Chandroo KP, Yue S, and Mocci RD (2004) An evaluation of current perspectives on consciousness and pain in fishes. Fish and Fisheries 5. 281-295

Chapman, CR and Nakamura Y (1999) A passion of the soul: an introduction to pain for consciousness researchers. Consciousness and Cognition 8. 391-422

Dugatkin LA, Wilson DS (1993) Fish behaviour, partner choice, and cognitive ethology. Rev Fish Biol Fish 3:368-372

Duzer EM van (1939) Observations on the breeding habits of the cut-lip minnow, Exoglossum maxillingua. Copeia 1939:65-75

Fricke H (1971) Fische als Feinde tropischer Seeigel. Mar Biol 9:328-338

Edelman GM and Tononi G (2000)A Universe of Consciousness. Basic Books, New York, NY

Glynn I. (1999) An Anatomy of Thought: The Origin and Machinery of the Mind. Wiedenfield and Nicholson

Geiger W (1956) Quantitative Untersuchungen über das Gehirn der Knochenfische, mit besonderer Berücksichtigung seines relativen Wachstums, I Acta Anat 26: 121-163

Grandin T. and Deesing M. American Board of Veterinary Practitioners - Symposium 2002 May 17, 2002, Special Session Pain, Stress, Distress and Fear. Emerging Concepts and Strategies in Veterinary Medicine

Griffin DR (1998) Animal Minds. The University of Chicago Press.

Grutter AS 1995 Relationships between cleaning rates and ectoparasite loads in coral reef fishes. Mar Ecol Prog Ser 118:51-58

Harmes CA, Lewbart GA, Swanson CR, Kishimori JM, Boylan SM (2005) Behavioural and Clinical Pathology Changes in Koi Carp (Cyprinus carpio) Subjected to Anaesthesia and Surgery with and without Intra-Operative Analgesics. Comparative Medicine Vol. 55 No. 3 221-226

Kacher H (1963) Opithognathus aurifrons (Opisthognathidae) Graben einer Wohnhöhle, Wallbau Film E514, Encyclopaedia Cinematographica. Institut für den wissenschaftlichen Film, Göttingen

Lachner A (1952) Studies of the biology of the cyprinid fish of the chub genus Nocomis of northeastern United States. Am Midl Nat 48:433-466

Laureys S., Faymonville ME, Luxon A, Lamy M, Franck G, and Maquet P (2000) Restoration of thalamocortical connectivity after recovery from persistent

Lovibond PF , Shanks DR (2002) The role of awareness in Pavlovian conditioning: empirical evidence and theoretical implication. Journal of Experimental Psychology 28 3-26

Maren S (2001) Neurobiology of Pavlovian fear conditioning. Annual Review of Neuroscience 24. 897-931

Marino L (2002) Convergence of complex cognitive abilities in cetaceans and primates. Brain, Behaviour and Evolution 59. 21-32

Milinski M, Pfluger D, Külling D, Kettler R (1990b) Do sticklebacks cooperate repeatedly in reciprocal pairs? Behav Ecol Sociobiol 27:17-21

Morris D (1958) The reproductive behaviour of the ten-spined stickleback (Pygosteus pungitius L.). Behaviour [Suppl] 6:1-154

Myrberg AA, Riggio RJ (1985) Acoustically mediated individual recognition by a coral reef fish (Pomacentrus portitus)

Myrberg AA, Montgomery WL, Fishelson L (1988) The reproductive behaviour of Acanthurus nigrofuscus (Forskal) and other surgeon fishes (Fam. Acanthuridae) of Eilat, Israel (Gulf of Aqaba, Red Sea). Ethology 79:31-61

Nowak MA, Sigmund K (1998) Evolution of indirect reciprocity by image scoring. Nature 393:573-577

Overmier JB, Hollis KL (1990) Fish in the think tank: learning, memory, and integrated behaviour. Neurobiology of Comparative Cognition (eds Kesner RP, Olson DS), Lawrence Erlbaum, Hillsday, NJ. pp. 205-236

Roberts G (1998) Competitive altruism: from reciprocity to the handicap principle. Proc R Soc Lond B 265:427-431

Rose, JD 2002 The neurobehavioural nature of fishes, and the question of awareness and pain. Rev. Fish. Sci. 10:1-38

Sneddon, LU 2003. The evidence for pain in fish: The use of morphine as an analgesic. Applied Animal Behavior Science. 83:153-162.

Zahavi A (1995) Altruism as a handicap—the limitations of kin selection and reciprocity. J Avian Biol 26:1-3

Fish Are Animals Who Do Things

If you find it hard to believe that fish feel pain, consider this!

Cognition—the ability to think—was an important factor in the establishment of whether fish could feel pain, and it happened that in the same year as Rose's article was published, Bshary, Wickler, and Fricke published a review of the findings on the cognitive capabilities of fish (Bshary et al 2002). Here are a few examples:

Recognition of others as individuals has long been established in many varieties of fish, both visually and acoustically (Myrberg and Riggio 1985). It forms the first step towards complex social lives, in which cognition is often most evident. I documented relationships among reef sharks for years. They, too, relate to each other individually.

Social learning is illustrated by the migrations of the surgeon fish (Acathurus nigrofuscus), described in detail by Arthur A. Myrberg Jr. in 1998. These fish leave their territories all over the lagoon, and travel in single file through paths in the coral to their traditional spawning grounds. They go and return along the same paths each night at precisely the same time, as I saw in the local lagoon, year after year. Their spawning ground was the only place along the lagoon's border where the outflowing current was exactly balanced by the incoming surge, so that the huge cloud of spawn that they left in the gathering night, stayed in place. These short term migrations had been shown to be the result of social learning; each generation of fish learned from its elders where to go to spawn, and when.

Triggerfish (Balistidae) often feed on sea urchins. Usually, they try to ‘blow’ them onto their side to get access to the unprotected body parts beneath. Hans Fricke (1971) observed at Eilat how five different individuals of Balistapus undulatus sucessfully hunted sea urchins by first biting off the spines, which allowed them to grab the urchin and take it to the surface. They fed on the unprotected parts underneath while the urchin slowly sank. In spite of decades of observations, Fricke never saw this behaviour anywhere else. It appeared to be the result of social learning.

Intertidal gobies (Gobius soporator), live in tide pools, and during low tide they can jump from one to another, without being able to see their target pool at the beginning of the jump. Experimentation showed that the fish had memorized the lay of the land around the home pool by swimming over it when the tide was in, so were referring to a three dimensional memory to navigate when the outgoing tide left them only a labyrinth of pools. (Aronson 1951, 1956).

With the exception of humans, fish are more skillful than primates at nest building. At least 9000 fish species build some sort of nest, either for egg laying or for protection.

The male minnow Exoglossum selects more than three hundred stones, all of the same size, from over 5 m distance, to build a spawning mound 35 cm wide and 10 cm high (van Duzer 1939). Another fish builds dome-shaped nests from 10,000 pebbles (Lachner 1952).

The jawfish, (Opistognathus aurifrons), collects stones of various sizes to build a wall, leaving a hole just big enough to pass through. This involves repeated rearrangement of the stones. In between, the fish searches for new stones that might better fit the available space than the ones it has already collected, using flexible behaviour depending on the circumstances (Kacher 1963; Colin 1972, 1973).

Another example showing surprising flexibility of behaviour is the ability of the ten-spined stickleback (Pygosteus pungitius), to build his nest around the eggs if the female has already laid them, though he usually builds the nest first (Leiner 1931). Great care is required, and a different technique has to be used to avoid damaging the eggs. Since those eggs do hatch, the males achieve their goal. (Morris 1958)

Redouin Bshary (2002), described seeing cooperative hunting between red sea coral groupers (Plectropomus pessuliferus), or lunartail groupers (Variola louti), and giant moray eels (Gymnothorax javanicus):

“These two large species of groupers were observed regularly approaching the eels that were resting in a coral cave, and shaking their bodies in exaggerated movements, usually at less than 1 m distance to the moray eel.... In 7 of 14 observations, the moray eel left its cave and the two predators would swim next to each other, searching for prey. The groupers would often come so close that the two predators touched each other at their sides. While the moray eels sneaked through holes, the groupers waited above the corals for escaping fish.”

Another unusual form of cooperation among different species is seen in cleaning symbiosis. Cleaner fish come from many different fish families, and depend on cleaning for their diet to varying degrees. They clean the dead skin and ectoparasites from their clients in return for a meal. Full time cleaners may have about 2,300 interactions per day, with clients belonging to 100 different species! (Grutter 1995)

According to the evidence, cleaners have their hundred client species categorized as those who only come to their local cleaner, and those whose home ranges include the territories of other cleaners. For the latter, they have competition, so give them priority over the locals, who have no choice of cleaner.

Cleaners sometimes “cheated” by feeding off the client's healthy flesh as well as doing the usual cleaning job, and the clients with no choice of cleaner punished the cleaner by aggressively chasing it, and inflicting a bite or two, as they saw fit. (Clutten-Brock and Parker 1995). But these clients benefited in the future, because the cleaner fish were seen to give them, but not others who visited in the meantime, a better-than-average cleaning service on the next visit! Apparently cleaners can distinguish more than 100 individual clients belonging to various species.

Cleaners will hover above the client and touch it with their fins, in an effort to influence its decision to come for a cleaning. This touching tactic is also used to try to reconcile with a client whom they have cheated as described above. Cleaners even exploit the presence of a third party in an attempt to make aggressive clients stop chasing them by going to a nearby predator and caressing it, so that the client dares not continue the chase!

Cleaners will behave altruistically toward their clients if they are being watched by potential new clients—but only those who could visit another cleaning station. Since clients will emulate the behaviour of the former client, the sight of another being treated very well by the cleaner, is more likely to convince it to come for servicing than seeing another client being chased or eaten! This tactic suggests a short term image, or social prestige (Alexander 1987; Zahavi 1995; Nowak and Sigmund 1998; Roberts 1998), that determines their success in attracting new clients.

Such complex social behaviour—cheating, reconciliation, altruism, species recognition, individual recognition, punishment, social prestige, and bookkeeping, displayed by full-time cleaners 50 to 100 times per day, is generally considered to indicate consciousness when displayed in primates.

A similar example of social judgement is given by predator inspection, in which different individuals take turns to lead others away from the school to look over a predator. Fish who don't take their turn cooperatively, will not be trusted by their partners in the future. In other words, the fish make an evaluation of the behaviour of another individual, remembers it, and takes it into account in future decisions. (Milinski et al. 1990b; Dugatkin and Wilson 1993)

At the end of the review of cognition in fish, Bshary wrote: “We are aware of only one experimentally shown qualitative difference in mechanisms between primates and fish, and this difference is the ability to imitate.”

References

Alexander RD (1987) The biology of moral systems. Aldine de Gruiter, New York

Aronson LR (1951) Orientation and jumping behavior in the goby fish Bathygobius soporator. Am Mus Novitates 1486

Aronson LR (1956) Further studies on orientation and jumping behaviour in the goby fish Bathygobius soporator. Anat Rec 125:606

Bshary R, Wickler W, Fricke H (2002) Fish cognition: a primate's eye view. Animal Cognition (2002) 5 : 1-13

Colin PL (1972) Daily activity patterns and effects of environmental conditions on the behaviour of the yellowhead jawfish Opistognathus aurifrons, with notes on its ecology. Zoologica 57:137-169

Colin PL (1973) Burrowing behaviour of the yellowhead jawfish, Opistognathus aurifrons. Copeia 1973:84-90

Barber TX (1993) The Human Nature of Birds. Bookman Press, Melbourne

Clutten-Brock TH, Parker GA (1995) Punishment in animal societies. Nature 373:209-215

Chandroo KP, Yue S, and Mocci RD (2004) An evaluation of current perspectives on consciousness and pain in fishes. Fish and Fisheries 5. 281-295

Chapman, CR and Nakamura Y (1999) A passion of the soul: an introduction to pain for consciousness researchers. Consciousness and Cognition 8. 391-422

Dugatkin LA, Wilson DS (1993) Fish behaviour, partner choice, and cognitive ethology. Rev Fish Biol Fish 3:368-372

Duzer EM van (1939) Observations on the breeding habits of the cut-lip minnow, Exoglossum maxillingua. Copeia 1939:65-75

Fricke H (1971) Fische als Feinde tropischer Seeigel. Mar Biol 9:328-338

Edelman GM and Tononi G (2000)A Universe of Consciousness. Basic Books, New York, NY

Glynn I. (1999) An Anatomy of Thought: The Origin and Machinery of the Mind. Wiedenfield and Nicholson

Geiger W (1956) Quantitative Untersuchungen über das Gehirn der Knochenfische, mit besonderer Berücksichtigung seines relativen Wachstums, I Acta Anat 26: 121-163

Grandin T. and Deesing M. American Board of Veterinary Practitioners - Symposium 2002 May 17, 2002, Special Session Pain, Stress, Distress and Fear. Emerging Concepts and Strategies in Veterinary Medicine

Griffin DR (1998) Animal Minds. The University of Chicago Press.

Grutter AS 1995 Relationships between cleaning rates and ectoparasite loads in coral reef fishes. Mar Ecol Prog Ser 118:51-58

Harmes CA, Lewbart GA, Swanson CR, Kishimori JM, Boylan SM (2005) Behavioural and Clinical Pathology Changes in Koi Carp (Cyprinus carpio) Subjected to Anaesthesia and Surgery with and without Intra-Operative Analgesics. Comparative Medicine Vol. 55 No. 3 221-226

Kacher H (1963) Opithognathus aurifrons (Opisthognathidae) Graben einer Wohnhöhle, Wallbau Film E514, Encyclopaedia Cinematographica. Institut für den wissenschaftlichen Film, Göttingen

Lachner A (1952) Studies of the biology of the cyprinid fish of the chub genus Nocomis of northeastern United States. Am Midl Nat 48:433-466

Laureys S., Faymonville ME, Luxon A, Lamy M, Franck G, and Maquet P (2000) Restoration of thalamocortical connectivity after recovery from persistent

Lovibond PF , Shanks DR (2002) The role of awareness in Pavlovian conditioning: empirical evidence and theoretical implication. Journal of Experimental Psychology 28 3-26

Maren S (2001) Neurobiology of Pavlovian fear conditioning. Annual Review of Neuroscience 24. 897-931

Marino L (2002) Convergence of complex cognitive abilities in cetaceans and primates. Brain, Behaviour and Evolution 59. 21-32

Milinski M, Pfluger D, Külling D, Kettler R (1990b) Do sticklebacks cooperate repeatedly in reciprocal pairs? Behav Ecol Sociobiol 27:17-21

Morris D (1958) The reproductive behaviour of the ten-spined stickleback (Pygosteus pungitius L.). Behaviour [Suppl] 6:1-154

Myrberg AA, Riggio RJ (1985) Acoustically mediated individual recognition by a coral reef fish (Pomacentrus portitus)

Myrberg AA, Montgomery WL, Fishelson L (1988) The reproductive behaviour of Acanthurus nigrofuscus (Forskal) and other surgeon fishes (Fam. Acanthuridae) of Eilat, Israel (Gulf of Aqaba, Red Sea). Ethology 79:31-61

Nowak MA, Sigmund K (1998) Evolution of indirect reciprocity by image scoring. Nature 393:573-577

Overmier JB, Hollis KL (1990) Fish in the think tank: learning, memory, and integrated behaviour. Neurobiology of Comparative Cognition (eds Kesner RP, Olson DS), Lawrence Erlbaum, Hillsday, NJ. pp. 205-236

Roberts G (1998) Competitive altruism: from reciprocity to the handicap principle. Proc R Soc Lond B 265:427-431

Rose, JD 2002 The neurobehavioural nature of fishes, and the question of awareness and pain. Rev. Fish. Sci. 10:1-38

Sneddon, LU 2003. The evidence for pain in fish: The use of morphine as an analgesic. Applied Animal Behavior Science. 83:153-162.

Zahavi A (1995) Altruism as a handicap—the limitations of kin selection and reciprocity. J Avian Biol 26:1-3

Keep the Secrets of the Sea

In January an in-depth study of the current depletion of sharks was published (Worm et al 2013). It revealed that the numbers of sharks killed for shark fin soup are not falling, that no sharks have been saved, and that the ravenous market for the infamous party soup continues to be fed, in spite of the increase in support for shark protection that has come in the last decade.

A review of the way our society treats sharks reveals almost no segment in which they are respected, with the exception of certain researchers, divers and veterinarians. Their fins are taken for soup by the Asians, they are vilified by Shark Week in the west, they are wrestled and stabbed by scientists for a few minutes of glory as a he-man “shark fighter” on National Geographic or the ill-termed “Discovery Channel,” and they are fished as sea monsters by “sportsmen.” Television with its monster shows has unleashed an out pouring of hatred that has allowed them to be massacred in full view with almost no public outcry nor protest, and the idea that they should be exterminated stands in the way of protecting them from extinction. Even science often measures the numbers of sharks it kills in the metric tons, with no regard for any individual.

And no one weeps for sharks.

But this is the point :

Much research, including some sponsored by certain NGO's who claim to be working for their protection, is geared to finding out where sharks are, how many are there, and announcing that information amid as much fanfare as possible, often using the unpleasant blood and teeth slant of Shark Week or National Geographic as the medium to dramatize the information to the maximum.

What is wrong with this picture?

This is exactly what shark finners want to know—where sharks are!

Since shark fin is the most valuable seafood, surely no one who is actually concerned about their welfare would ever reveal such information. Look what happened to the sharks using the much publicized shark “superhighway” off the west coast of Central America. It attracted shark finners en masse and it was the sharks who paid for this grand discovery. Some secrets of the sea should remain secret.

Why is this information being so widely tooted by those who claim to be protecting sharks? Because its easy to get with modern equipment, so with little invested, a dramatically announced discovery can lead to many more millions in donations? Possibly. There must be some reason for it.

I implore you to think twice about aiding and abetting such efforts by revealing the location, species, or numbers of the sharks you see while diving.

If you learn where sharks are do not tell anyone. If you see sharks on a dive, do not report their location or numbers to anyone. Do not get attached to any place, to any underwater beauty, if you don't want your heart to be broken.

We all read all the time about the millions of sharks being finned all over the world, figures that seem unreal. I assure you that they will no longer seem unreal if you go diving, and find the sharks you loved to be with lying alive and finless on the bottom of the dive-site instead of circling majestically around you. Then even if its only one million sharks you find, or maybe only twenty five, you will find that the psychological effect is a lot more intense.

As an analogy, it is disturbing to hear that some dogs elsewhere were poisoned. But if it was your dogs who were poisoned, you reel.

Sharks Lack the Bite Reflex we know in Mammals

During my seven year study of the behaviour of wild reef sharks, I had many opportunities to observe them under circumstances in which I expected them to bite, as a dog or other mammal would tend to do. Yet they did not. Further, while the sharks had preferred companions, I never saw them fighting with each other. They appeared to have friends, but no enemies.

For years people had told me, and I half believed myself, that one day I would be bitten and would bleed to death, or faint and drown. Since I was alone far from shore as night was falling, I could expect no one to save me. These circumstances enhanced what appeared to be an instinctive tendency to react with darkening consciousness and soaring terror to certain visual cues. So I had long acquaintance with the phenomenon of fear. Often it took all my psychological force to compose my mind in order to overcome it.

When things went wrong, I would find myself in tossing waters opaque with blood and excited sharks, in a situation for which I was unprepared. Yet, no matter what happened, no shark bit me, time after time.

All other species, wild and tame, with whom I had a fraction of the intimacy I shared with sharks had bitten me sooner or later, either by accident or in a fit of pique. Even my pet dog sometimes grabbed my hand in her teeth along with the offered cookie.

Why had none of those hundreds of sharks of four different species, some many times my size, ever bitten me? I would watch Martha, my favourite, coil through the sea in front of my face, snapping up the treats I was freeing for her while ignoring my hands and the little plastic bag I had brought them in, and be convinced that it could not be a random coincidence.

There had to be a reason.

One night I accidentally kicked a shark with all my force, not realizing that the six foot animal was between my legs as I finned upward to reach into my kayak. Horrified, I peered underwater to scrutinize the situation, expecting her to instantly turn and slash. But there was no change in either her speed nor trajectory as she curved around to lazily circle me.

It was then that I realized that I was expecting a reaction from a shark that was based on my experiences with mammals. As mammals, we share the automatic biting reflex displayed by dogs, cats, primates, rats, and even vegetarian mammals. Anyone who has been seriously assaulted knows that the instinct to bite in self defence is very thinly veiled beneath our civilized daily lives. It is an automatic reflex that we take for granted.

But that night, I realized that these requiem sharks must lack this bite reflex.

Our fear of sharks is based on the intrinsic knowledge that we, and animals like us, instinctively bite in aggression or fear. We just naturally assume that sharks will too.

But they don't.

Sharks do not share this biting reflex with us, and that is the missing key. With their big mouths and shocking sets of teeth, our imaginations are undone as we consider them opening to bite us. But in fact, they bite only to eat, not to injure another animal.

On the contrary, they seem to have an inborn inhibition against biting companion animals. They don't regard us as prey, so they apparently view us as other animals who share their ecological community.

Even the great white shark has been shown by Dr. Peter Klimley to ritualize conflict when ownership of a seal prey comes into question. The shark who can splash water farthest with its tail wins the seal, so a physical battle, which would gravely harm both sharks, given their dentition, is avoided.

Unfortunately, our instinctive fear has been used by the media to entertain us with horror shows, starring sharks as the only known monsters in the sea. The wide spread shark attack hysteria that has resulted from years of such misrepresentation of sharks is one of the great obstacles to shark protection. Examples are the movie "Jaws" and Discovery Channel's highly profitable annual "Shark Week."

Given the numbers of people using the oceans for recreation, it is actually remarkable that so few are accidentally bitten by members of this highly evolved and intelligent, predatorial class of animals. Far more people are bitten to death by cats and dogs, slain by lightning or falling coconuts, or murdered by their own species.

For further information, my book "My Sunset Rendezvous : Crisis in Tahiti" meticulously describes the counter-intuitive behaviour the sharks displayed with me underwater, over the 15 years that I spent observing them in French Polynesia. 

Ila France Porcher

The Value of Ethology

While I preferred to study sharks directly through underwater observation, shark researchers often choose tagging methods which allow them to gain certain types of data remotely. The advantages of this method are evident, but the loss of contact with the animal itself results in a dramatically impoverished understanding of them.

A good example is the recently announced study concluding that grey reef sharks swim at different depths depending on the phase of the moon. (link here)

No mention of the effect of the moon on the sharks' general behaviour or subjective states was mentioned. The trouble is that it was not just ignored, it was not even seen. So the study is a dismal, one dimensional report, that might as well refer to robots, for all the understanding it provides of sharks. The hype with which the “finding” was announced also failed to acknowledge the many others over time who have noted that sharks, like other animals, use both of this planet's sources of illumination. 

While the researchers conclude that they hope that this information will aid in conservation, it could very well be used to aid fishing and finning efforts, and in creating and magnifying the distance between animal and researcher, the study points to the worrying way in which animals in general, and sharks in particular, are objectified by science.

My reason for observing the local sharks underwater was to learn what they are like as animals and individuals. But pure research is not favoured by the scientific establishment, which directs the course of its own path through funding. The only reason that no one had established the gestation period of my subjects before me, for example, was the total lack of scientific interest in it.

By explaining the world from the perspective and to the advantage of its dominant groups, the scientific establishment can ignore the search for truth while furthering the dogma and so-called needs of the industrialized society. Attention is shifted away from the subject at hand, and interferes with its objective appraisal in a form of intellectual hypocrisy. In this case it is the diminution of the wild animal concerned that results—the diminution of sharks.

When I first began looking through the Internet for information on sharks, the entry of the word into any browser resulted in the word “attack” coming up. Now, the shark finning crisis has inspired many people to view sharks as victims which need to be saved. But are we closer to learning what these mysterious marine animals are actually like? I wonder. Not even the “JAWS” dogma has been left behind yet.

One of ethology’s major principles is to “know your animal,” by observing its behaviour closely over an extended period of time. That is why the ethological approach can be vital in providing complimentary information to the tagging studies so conveniently employed to the detriment of the search for understanding of the true nature of sharks.

For more information about what sharks are like, including detailed information about how the lunar cycle affects not only the short and long term roaming of sharks, but their subjective states and social lives, see “My Sunset Rendezvous : Crisis in Tahiti.”

STOP Shark Fins at the B C Coast : A Petition!

Sign now : http://www.thepetitionsite.com/681/363/318/block-shark-fins-at-the-bc-coast/

Given the decision by Canada's federal government to support the shark finning business by defeating Bill C-380, British Columbia must act at once to block shark fins from entering Canada via its west coast.

California, Oregon, and Washington states have already made it illegal to trade, possess, or distribute shark fins, leaving British Columbia as the only remaining entry point for shark fins on the west coast of North America.

Across the Pacific Ocean the sharks inhabiting vast archipelagoes of islands are being massacred to supply the voracious market for the costly party soup across North America.

By halting this province’s contribution to the crisis, we will broadcast the strong message that British Columbia refuses to play a role in driving so many species of sharks to extinction.

The facts :

• Shark fin soup is a vanity dish.
• The monetary value is so high that much of the trade is in criminal hands.
• The shark fin business shows no respect for other cultures, slaughtering sharks in incalculable numbers on the coast of every country with a tropical or temperate coastline, including countries in which sharks are held sacred, and regardless of legal protections.
• Threats, intimidation and murder, especially of journalists and researchers are commonplace in the business.
• In a protein starved world, the waste represented by cutting off only 3 percent of each of tens of millions of animals and discarding the rest, is indefensible.
• Every second at least three sharks are finned for shark fin soup.
• Between 63 and 273 million sharks slaughtered annually represents an unsustainable massacre that is driving one third of shark and ray species to extinction.
• The destruction of endangered species is unacceptable under any pretext.

An oceanic crisis has been precipitated by the shark finning business. Shark populations world-wide have plummeted by 90 percent, with some populations at 1% of pre-1985 levels. The decline is comparable to the loss of buffalo from the great plains two hundred years ago, but on a global scale. The elimination of the top predators from all oceans will ultimately be reflected in comparable ecological upheavals world-wide; some are already apparent.

So we respectfully ask Premier Christy Clark, in concert with the government of British Columbia, to take leadership in this crisis, and close the door. Please act swiftly to block shark fins from entering the continent via British Columbia, and declare a total ban on the importation, exportation, possession and trade of shark fins in the province.

Ila France Porcher

Open Letter to the B.C. Government

Sadly, the Government of Canada has voted to support the shark finning business. So I, and many other shark advocates in British Columbia are demanding a total ban on shark fins in the province. This is an open letter I have just sent to the members of the B.C. Government asking that they act swiftly to block shark fins at the B.C. coast.

Dear Honourable Members, 

Given the federal decision to support the shark finning business, we are writing to urge you and your government to ban the importation of shark fins into Canada via its west coast, and make it illegal to import, export, trade, possess or distribute shark fins. By halting this province’s contribution to the crisis, you will broadcast the strong message that British Columbia refuses to play a role in driving so many species of sharks to extinction.

The destruction of endangered species cannot be acceptable under any pretext. Further, in slaughtering sharks in incalculable numbers on the coast of every country with a tropical or temperate coastline regardless of legal protections, and including countries in which sharks are held sacred, the shark fin business shows a total lack of respect for other cultures. The monetary value is so high that much of the trade is in criminal hands, and has resulted in threats, intimidation and murder, especially of journalists and researchers.

Shark fin soup is a vanity dish: its cost is a supposed measure of the wealth of the buyer and his ostentatious largesse to give and receive honour, with its alleged magical properties an excuse for consumption. But in a protein starved world, the waste represented by cutting off only 3 percent of each of tens of millions of animals for consumption and discarding the rest, is indefensible. 

An oceanic crisis has been precipitated by this practice. Shark populations world-wide have plummeted by 90 percent, with some populations at 1% of pre-1985 levels. The decline is comparable to the loss of buffalo from the great plains two hundred years ago, but on a global scale. The elimination of the top predators from all oceans will ultimately be reflected in comparable ecological upheavals world-wide; some are already apparent.

Every second at least three sharks are finned for shark fin soup—the latest estimate is between 63 and 273 million sharks slaughtered annually, an unsustainable massacre that is driving one third of about one thousand shark and ray species into extinction.

In recognition of this immense problem, California, Oregon, and Washington states have made it illegal to trade, possess, or distribute shark fins. So we respectfully ask that you act swiftly to block shark fins from entering the continent via British Columbia, and declare a total ban on the importation, exportation,  possession and trade of shark fins in the province.

Please feel free to share and send it on!

Shark Fishing : Experiments in Mega Death || CITES grants sharks protection

Delegates at the CITES conservation meeting in Thailand's capital, Bangkok, have voted to extend protection under Appendix II  to all three species of hammerhead sharks, the porbeagle shark, the oceanic white tip shark, and manta rays. This represents a decisive step in the right direction in terms of limiting commercialization and trade of these hard pushed sharks and their relatives, the rays. 

When I discovered sharks in the South Pacific in the nineties, you could still meet white tipped oceanic sharks exploring outside the reef, and when I asked a dive master about them being finned, he said, so what? They are among the most abundant animals on the planet. Not any more. While I was there they vanished, and the dolphins and reef sharks once preyed upon by the oceanic sharks no longer appeared with shark-bite scars, and increased in number. And the reef sharks were fished beginning in 2003.  Those are the most remote islands in the pacific, so if the pelagic species are gone from there, they are likely not more numerous closer to the continents. Asian divers say it is hard to find sharks in Asia, there are problems with the finning of the sharks off Africa, and the same story is echoed around the globe by eye-witnesses on location. 

In the Mediterranean Sea, in the heart of Europe, scientific analysis of available data indicates that formerly common sharks have declined by 99.9 percent, and in other large oceanic regions such as the Gulf of Mexico, sharks have been depleted to a similarly tiny fraction of their pre-industrial level.

Looking out across the planet, the loss of sharks compares with the loss of buffalo from the American plains but on a global scale, a daunting loss of life that no one in their right mind would consider normal or sustainable. Imagine seeing only a few birds where once you saw clouds of birds filling the skies. That is the kind of loss the accessable free swimming species of sharks have experienced. 

Thank you to the delegates at CITES for taking this much needed step!

Blackfin Reef Shark Evacuation from Moorea Island, 2002

Blackfin reef sharks (Carcharhinus melanopterus) reside in the lagoons and on the outer slope of the barrier reefs of Moorea Island. This coral habitat is shallow enough to facilitate underwater observation of the species. Regular observation at different sites centering in the Vaihapu region (Galzin and Pointer 1985) yielded a large amount of data on their movements, ethology, and social biology between 1999 and 2007 (Porcher 2005). In 2002, all blackfin reef sharks under observation, not only by the author but also by the dive clubs holding shark dives, left the north shore of the island for a period of ten days to two weeks. This event suggests an unknown pattern or influence at work.

With the surprising new information from Johann Mourier, that these sharks easily travel between islands, I'm re-posting my account of their unexplained and unprecedented disappearance from Moorea Island in late July, 2002.

Johann began studying the same sharks that I observed, using far more high-tech methods, just as I was leaving the island, and has worked within the scientific community in French Polynesia to make sure that they stay protected, while unfolding many mysteries about these interesting sharks.

http://johannmourier.wordpress.com/

Recently he discovered that this apparently sedentary species actually swims easily to other islands! They seem content to stay in their favored region of the coral garden—most particularly the matronly lagoon females—but if an adult female goes to another island to birth, thereby returning to the place she originated, it follows that she must have initially changed islands when still a juvenile! 

I often noted surprising roaming patterns in the lagoon juveniles—they seemed to travel widely before settling down into a home range at the age of about four. And males disappearing for months at a time during the reproductive season could have been going much farther than I imagined. Then there is the remaining mystery of how such reef-loving sharks got to these islands in the first place, since they result from volcanic eruptions in the relatively recent geological past, and are so far from the continents. Johann's finding indicates that these reef sharks are quite capable of oceanic navigation and travel.

If you learn of a similar event, involving the temporary disappearance of a community of sharks from its ranges, I would be glad if you would contact me by e-mail. Thank you!

The Event :

On the evening of Saturday, July 20th, 2002, I found many visiting male blackfins in the lagoon, though it was not the reproductive season when they usually visited. The resident females were absent which was highly unusual, and so were nearly all the older juveniles. The small juveniles, including sharks less than one year old, who usually remained hidden in certain regions of thick coral, were absent that night.

One of the visiting males appeared highly agitated, twitching wildly with successive instantaneous directional changes throughout the period in which he was present, a behaviour pattern I had only noted before in sharks after being startled, and then normally in juveniles. I had never seen an adult shark behave like this for so long (20 minutes) and later associated the episode with the unique event which followed.

On July 23rd, 2002, the divers conducting daily shark dives outside the barrier reef, and the commercial tours holding shark feeding sessions in separated lagoons on the north shore of Moorea (see map), reported that no sharks had appeared that day, something that had never happened before. Only Phillipe Molle, of M.U.S.T. Dive Club, Maharepa, said that he had been holding shark dives for 17 years and on only one other occasion had no sharks attended, on the day before a hurricane struck the island. He was expecting bad weather, but none came.

No sharks were seen for the next five days, with the exception of two sightings of “small sharks” who passed in the distance and did not approach. Usually these shark dives were frequented by approximately twenty to thirty male blackfin reef sharks, who met dive boats at the site and swam without fear among the divers during the dive.

These were the only places on the island where the species was regularly observed, so the actual extent of the evacuation is unknown. 

The juvenile males began to reappear first. I identified one on July 28^th, and one resident female came back by herself to my study area on Tuesday, July 30^th. But the majority of lagoon residents, the females and many more juveniles, returned on Friday, August 2^nd. They appeared to be on the move, travelling swiftly along the lagoon from west to east, displaying no socializing behaviour nor casual circling. Many had their home ranges to the west, and within the next days most had settled back into their home ranges. Though a few more sharks returned later, the majority of the lagoon residents returned that evening, travelling swiftly together, widely spread out across the coral landscape.

By mid-August their behaviour and distribution was nearly back to normal, but a major disruption had occurred. In some parts of the lagoon, the pattern of sightings I had systematically recorded prior to the disappearance took months to re-establish itself. Some adult residents never returned, and a high fraction of the small juveniles I had identified as inhabiting the protected areas of thick coral, never returned.

The approximately 10 day evacuation involved the populations of C. melanopterus from at least two lagoons (separated by a wide, deep bay) who normally don't interact. Adult females and juveniles of all ages, as well as the entire population of males who live outside the barrier reef, left.

Discussion

Intensive investigation of the shark evacuation revealed no applicable reason for it. There was no sudden fishing effort that could have caused the sharks to flee, no pollution event, the weather was normal, the water temperature was normal, there were circle island tours moving around the island daily who reported nothing unusual, such as an incidental food source which could have attracted the sharks into the ocean. Such a food source would be visible from far away due to the vast muli-species congregation of seabirds which would be circling above it.  No other species appeared to be affected, though at that time of year I did not normally see nurse sharks, Nebrius ferrugineus., and reef white-tips, Triaenodon obesus, so regularly in the lagoon. I did not see any of these species of sharks while searching for C. melanopterus, but whether they had also evacuated was unverifiable. Female grey reef sharks, Carcharhinus amblyrhynchos appeared as usual, however, off the north-west corner of the island, which was the only dive site where they were regularly seen.

There were no military events in the area, and no earth tremors. On one of the days in which no sharks had been seen at any of the sites, humpback whales were resting in the bay with a group of spinner dolphins. Whatever had affected the sharks was not troubling the whales. Dr. Michael Poole, a marine biologist observing the whales and dolphins daily along the north shore, and frequently down the west coast and around the entire perimeter of the island, reported no change in the patterns of the movements of the marine mammals and nothing unusual in the ocean during this period.

The oceanic current does not move fast enough to explain the return of the sharks in such a short period if oceanic conditions were responsible for the evacuation (personal communication from Arthur A. Myrberg Jr.).

The occasional appearance of a juvenile shark on the limits of visibility could be a clue that the sharks were in deeper water. The reluctance to approach to eat is typical of a shark alone. It is possible that the larger sharks had gone much deeper for unknown reasons, while the juveniles preferred shallower water, so were the ones who came into visible range of divers at about 22 m in depth.

Though I contacted every elasmobranchologist I knew, posted an inquiry on the elasmo-list shark discussion board, and received many interested replies, no one reported having seen nor heard of any similar event, nor did anyone have a plausible explanation.

Professor Myrberg considered the evacuation to be in the category of things that cannot be explained at this time.

While the reason for the spontaneous evacuation of Carcharhinus melanopterus from the north shore of the island between July 23, and August 3, 2002, could not be explained, the one factor that suggested that it was a natural event was that it occurred during the period of the full moon, a time favoured by individuals for roaming.

References

Galzin R, Pointer JP (1985) Moorea Island, Society Archipelago. In: B Delesalle, R Galzin & B. Salvat (Eds). 5th International Coral Reef Congress, Tahiti, 27 May to 1 June 1985. Volume I: French Polynesian Coral Reefs: 73-102
Porcher IF (2005) On the gestation period of the blackfin reef shark, Carcharhinus melanopterus, in waters off Moorea, French Polynesia. Mar Bio 146: 1207-1211

see also : Mourier, J. & Planes, S. (2013). Direct genetic evidence for reproductive philopatry and associated fine-scale migrations in female blacktip reef sharks (Carcharhinus melanopterus) in French Polynesia. Molecular Ecology 22 (1): 201-214.