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Home , Hexanchiformes, Whale shark

BODY MARKINGS OF THE WHALE : VESTIGIAL OR FUNCTIONAL?

By STEVEN G. WILSON Department of Zoology, The University of , Nedlands, WA 6907, Australia *Current address: Department of Zoology, University of New Hampshire, Durham, NH 03824, USA and R. AIDAN MARTIN ReefQuest Centre for Shark Research, P.O. Box 48561, 595 Burrard Street, Vancouver, BC V7X 1A3, Canada

ABSTRACT The ’s distinctive body markings are similar to those of other orectolobiform . These markings likely conceal their sluggish, bottom-dwelling relatives through disruptive colouration. It is argued here that the whale shark’s body markings similarly function to camouflage them in their pelagic environment. The whale shark’s countershaded colouration eliminates the optical appearance of relief against its visual background. Disruptive patterns resembling elements common in its environmental background break up the whale shark’s outline. Other possible functions for the whale shark’s markings are considered, including: radiation shielding, intraspecific communication ( recognition, sex recognition, postural displays, schooling coordination), and interspecific communication (aggressive mimicry). However, they are either discounted or evidence substantiating these functions is found to be lacking.

INTRODUCTION globe (Compagno 1984; Colman 1997; Eckert and Stewart 2001), Prior to 1986, there had been including Ningaloo Reef, Western only 320 reported sightings of Australia. Consequently, there is the whale shark, Rhincodon increasing research interest into typus (Orectolobiformes, the biology of whale sharks. In Rhincodontidae), worldwide addition to being the world’s (Wolfson 1986). Today they can be largest living and possessing a reliably encountered and studied distinctly unique body form, one in several locations around the

118 of the whale shark’s most striking relevance (Myrberg 1991). In features are its body markings, the essence, logical inference and function of which has only been circumstantial evidence can be briefly speculated about in the meaningfully applied to the literature. The purpose of this interpretation of morphology. paper is to review the possible Such intuitive methods can relevance of these markings to the provide ethologists with testable life history and biology of the hypotheses that potentially whale shark. explain a suite of observations Despite their being among the under a logically consistent most abundant large on theoretical model. However, earth, our knowledge of the interpretations divorced from behaviour of sharks in the wild is their normal environmental con- almost non-existent. Myrberg text (including social dynamics, (1976; 1991) and Gruber and prey behaviour, oceanographic Myrberg (1977) have recognised the conditions, etc.) should be applied difficulties arising from studies of cautiously until such time that sharks in captivity and in the they can be supported by direct field. For most species, captive observation and experimentation. environments cannot be created to adequately simulate natural settings to ensure ‘natural’ DISCUSSION behaviour. Field studies are often even less favourable. Many species BODY MARKINGS are fast-moving or far-ranging, Dorsally, the whale shark’s basic while some are dangerous to colouration is blue, grey, or observers (Johnson and Nelson brown, while ventrally it is white 1973; Myrberg et al. 1972), leading to (Last and Stevens 1994). Overlying logistical and methodological this dark dorsal background is a constraints that combine to make distinctive checkerboard pattern the cost and effort of research composed of pale spots, vertical prohibitive (Myrberg 1991). As a bars and horizontal stripes (Figure result, scientific knowledge of the 1). At birth, all orectolobiform behaviour of sharks lags decades sharks have patterns of bars, often behind that known about large in the form of wide bands or terrestrial animals. saddles, and spots. However, in As these problems will likely most species these markings fade persist into the foreseeable future, or change with age (Dingerkus alternative ways of interpreting 1986). With the exception of the the adaptive roles of shark whale shark, all orectolobiform structures and features must be sharks are primarily benthic. considered. One accepted Benthic or bottom-dwelling approach to the study of shark sharks often possess bold body behaviour is based strictly on markings that most likely provide anatomical considerations, sup- camouflage through disruptive plemented with inference about colouration (Bass 1978). Within the their functional and behavioural order Orectolobiformes,

119 Figure 1. Adult whale shark, TL ca. 10.0 m.

Figure 2. Neonate whale shark, TL ca. 0.58 m.

120 Stegostoma is regarded as the dasypogon, less than1mTLare primitive sister taxon of orange-brown in colour and Rhincodon (Dingerkus 1986; typically inhabit water shallower Compagno 1988). The , than 10 m and are thus often Stegostoma fasciatum, is thus the encountered by divers. Larger whale shark’s closest extant individuals become increasingly relative. Juveniles possess vertical pale, the largest at 3 to4mTLare yellow bars and spots that break yellowish-white, and typically the background colouration into inhabit ever deeper water as they dark brown saddles (Compagno grow (down to a depth of at least 1984). When zebra sharks are 40 m) (R.A. Martin, pers. obs.). between 50 and 90 cm TL, these Similarly, young nurse sharks, saddles break up into small spots, Ginglymostoma cirratum, are which become more evenly spaced pinkish brown with small brown as the grows. or blue spots, while adults are a uniform chocolate brown and ONTOGENETIC CHANGE IN typically inhabit much deeper BODY MARKINGS water than juveniles (Carrier 1991; R.A. Martin, pers. obs.). Whale The ontogenetic change in sharks are born with markings pigmentation pattern in most similar to those of adults (Figure orectolobiform sharks raises some 2). Since whale sharks are not important issues. The change may thought to change their pelagic be related to the different habitats habitat substantially from used by neonates/ juveniles and neonate to adult, there may be no adults. Neonate/juvenile zebra selective pressure to change their sharks seem to live primarily in pigmentation pattern as they age. water deeper than about 50 m (R.A. Martin, pers. obs.). Such Cott (1940) uses the ‘ontogeny depths may represent a relatively recapitulates phylogeny’ argu- predator-free refuge for the young ment to account for the presence and this pattern partially explains of stripes and spots in the young why juveniles are so rarely of many open country predatory collected, and even more rarely cats, including as lions, pumas and seen by recreational divers, lynxes. The functional relevance compared with adults. The bold of these markings is questioned in zebra-pattern may function as cubs that are sheltered in dens or disruptive colouration, visually holes. Cats inhabiting wooded concealing the pups from surroundings, such as leopards, potential predators by breaking pumas and ocelots, generally up their bodies into a series of retain or intensify these patterns irregular shapes against the in adulthood. Cott (1940) suggests backdrop of benthic cover. The that stripes and spots may adults of this species are most represent a primitive pattern in commonly encountered by divers cats, accounting for their presence in sandy areas around reefs at in the young of open country depths of less than 30 m. Young species on ancestral rather than ecological grounds. This rather tassled , Eucrossorhinus

121 rigid application of Haeckel’s Law sharks observed at Ningaloo Reef could also be applied to the exhibit healed bite marks and/ or presence of bars and spots in have pieces missing from their orectolobiform sharks that lose fins (S.G. Wilson, pers. obs.). these patterns. But it raises the Neonate whale sharks have been question of why these markings found in the stomachs of a blue are retained in adult whale sharks. shark, Prionace glauca (Kukuyev 1996), and a blue marlin, Makaira VESTIGIAL mazara (Colman 1997). Are the whale shark’s distinctive To rapidly reach a size large pattern of body markings vestigial enough to avoid predation, many with no modern function? Their sharks put their energy into pigmentation pattern bears evi- somatic growth, delaying repro- dence to its phyletic relationship duction until relatively late in life with similarly marked benthic (Stevens and McLoughlin 1991). ancestors. However, the whale Whale sharks reach sexual shark is a that would maturity when ca. 9.0 m TL and not be viewed against a benthic aged in their late 20s (Wintner substrate. In classical Darwinian 2000). A female whale shark natural selection, retention of a harpooned off the coast of characteristic would be favoured in 1995 contained 301 embryos if it enhances survival and/ or (Joung et al. 1996), more than reproductive success or is at least double the number of embryos not deleterious in any way. reported in any other species of Alternatively, do the whale shark. Such high fecundity may shark’s body markings reflect an represent a mechanism to com- adaptation to its modern pelagic pensate for the delay in repro- lifestyle? The examination of this duction made to achieve a large question forms the substance of size. Large litters would also offset the remainder of this discussion. high neonate and juvenile mortal- Other possible explanations for ity resulting from predation. the whale shark’s body markings In the pelagic habitat of the whale include: shark, visual recognition by a predator would likely be achieved via any of three cues: colour, relief CONCEALMENT and outline (Cott 1940). It is the Many animals employ the use of elimination of these telltale signs cryptic colouration to conceal that is the key to effective themselves against their visual camouflage in the whale shark. To background. The degree of crypsis pass unnoticed in its environ- and the quality of concealment ment, the whale shark’s colour- are usually proportional with the ation must match that of its intensity of predation pressure visual background. Tropical seas (Endler 1978). There is evidence to are generally low in particulate suggest that young whale sharks matter and , making suffer significant mortality from them transparent to light of short predation. Many of the whale wavelengths and characteristi-

122 cally blue (McFarland and Munz colour is not the only way of 1975). However, a uniform blue achieving countershading. In colour would not allow it to obliterative countershading, avoid detection. Colour and certain patterns viewed from a brightness of the visual back- distance produce the same effect. ground vary considerably A pattern consisting of both light depending on the line of sight of and dark markings, such as stripes, the observer. This would be bars or spots, observed from or compounded by the unequal beyond what is termed the reflection of light, giving the ‘blending’ distance blends to form impression of relief through the a uniform half-tone. If the presence of light and shadow proportion of light to dark in the (Cott 1940). pattern increases, the colour tone will lighten. In this way, it is Countershading possible to produce a flat tone ranging from dark to light as one Countershading utilises differ- passes from the dorsal to ventral ences in dorsoventral colouration aspect. This effect is most evident to allow an animal to blend in in the whale shark at the abrupt with its visual background (Cott dorsal/ ventral colouration 1940). A countershaded fish is interface. But what advantage coloured dark dorsally and light does the use of blended patterns ventrally, visually matching the have over graded tones of dark ocean depths when viewed uniform colour? To a closer from above and the bright surface observer these conspicuous pat- when viewed from below. When terns would be clearly visible. It is viewed from the side, counter- not incompatible that the same shading eliminates the perception pattern could be used to both of relief by counteracting the increase and decrease visibility effects of dorsal lighting and (Denton and Rowe 1994). A ventral shading. Countershading pattern perceptible to nearby effectively renders the bearer observers would not necessarily be optically flat, destroying the resolved by distant predators or appearance of depth and de- prey. These patterns may be used creasing the likelihood of visual to visually deceive closer detection. Many pelagic are observers by other mechanisms. laterally compressed to minimise Furthermore, they may be used to detection from above or below communicate information to (McFarland and Munz 1975). other whale sharks and/ or Consequently, their dorsal colour- communicate misinformation to ation fades gradually down their predators and prey. flanks until lightly coloured on their ventral surfaces. The whale shark’s more fusiform cross- Disruptive colouration section, dorsoventrally flattened Under ideal conditions, back- anteriorally, favours a more ground matching colouration abrupt transition. combined with effective counter- The use of graded tones of a given shading renders an animal almost

123 invisible (Cott 1940). However, the reduce surface continuity by visual background of most breaking up the shark’s form into animals is constantly changing. meaningless shapes. The reticu- An animal that is cryptically lations are more consistent with coloured in graded tones of a the visual background than the given colour would stand out as a surface upon which they appear. patch of uniformity against a Viewed from an upwards angle dynamic background of varying against flickering surface water brightness and/ or colour. they appear to be a part of the Especially so in an animal as large natural environment. When the whale shark. It is this observed against the backdrop of continuity of surface and the the deep ocean, they may be appearance of an outline that perceived as flickering shafts of leads to recognition. Thus, for underwater sunlight. The spots effective concealment it is create the impression of a series of essential that the outline be small objects resembling a school obliterated. This is achieved of fish. It has already been argued successfully in many animals by that countershading renders the harnessing the optical properties bearer optically flat, causing an of disruptive patterns. Disruptive observer to look ‘through’ the patterns contain some elements animal. The combination of that closely match the countershading and disruptive background and others that stand colouration used by the whale out as distracting marks to disrupt shark draws the attention of an surface continuity. Strongly observer through the animal to contrasted tones, such as very what appears to be a series of small light patterns on a dark objects moving in the midst of background are most effective. flickering beams of light. The Since the disruptive elements outline passes unnoticed. draw the attention of the observer, they should pass for part Flicker fusion of the visual background. It has been established that the Many countershaded marine whale shark’s lightly coloured fishes superimpose patterns of patterns would be highly stripes, bars and spots over their conspicuous to a predator at close cryptic background colouration distances. Visibility may be (Cott 1940). Widespread in pelagic further enhanced by the con- teleosts, such as mackerel, tunas, tinuous movement of the animal and marlin, are dorsal through the water. Upon sighting vermiculations that grade into a predator, a young whale shark vertical bars on the flanks would likely attempt to flee with (McFarland and Loew 1983). Whale rapid burst of speed. Such a rapid sharks and young tiger sharks, movement across the predator’s Galeocerdo cuvier, possess these visual field may blend its markings, which appear to mimic background colouration and the wave-induced patterns of superimposed patterns into a sunlight. They likely function to uniform colour. Whale shark

124 pups would quickly transform surface waters, possibly exposed to from being highly visible to high levels of ultraviolet indistinguishable against their radiation (Colman 1997). For many background. To the predator, the organisms, exposure to high- visual stimulus would be similar intensity solar radiation is to that of a slow moving whale detrimental (Harm 1980; van shark viewed from beyond the Weelden et al. 1986), but mela- blending distance (indistinguish- nomas and dermal carcinomas are able against its visual back- unknown in sharks (Stoskopf ground). In this case, rapid 1993). Most of the dermal tumors movement rather than distance found to date on elasmobranchs would blend the patterns. have been fibroid in nature, most This form of cryptic concealment, likely attributable to foreign body known as ‘flicker fusion’, is well intrusions (C. Lowe, pers. comm.). documented in many species of Extensive exposure to ultraviolet- snakes (Pough 1976; Jackson et al. B radiation can lead to the 1976). During rapid escape formation of thymine dimers, movements, the conspicuous known to cause several types of black, red and yellow vertical dermal carcinomas or neoplasia in bands of coral snakes are reported other fishes and humans. to blend together into a uniform Animals shield themselves by dark brown colour, matching pigmentation that protects their normal visual background. ultraviolet sensitive tissue or by It is difficult to imagine that seeking microhabitats protected young whale sharks would be from ultraviolet light (Burtt 1981). capable of achieving the speed Lowe and Goodman-Lowe (1996) necessary to induce flicker fusion documented increases in the in large predatory sharks or integumental melanin of juvenile teleosts. Regardless, rapid move- scalloped hammerhead sharks, ments by a strongly patterned Sphyrna lewini, in response to animal may cause confusion in a increases in ultraviolet radiation, predator, creating the impression illustrating for the first time that the animal is moving faster ‘tanning’ in an aquatic . than it really is (Deiner et al. 1976). However, pronounced darkening McFarland and Loew (1983) is reported to be a common suggest that the vertical stripes reaction to capture stress in may serve to confuse predators in juvenile lemon sharks, Negaprion another way, by disrupting their brevirostris, maintained in an fixation. Viewed against indoor pool at the University of flickering surface waters, these Miami (B.M. Wetherbee, pers. patterns may be alternately visible comm.). and invisible in a fish that The dark background of the constantly changes direction. whale shark’s countershaded dorsal surface could clearly help RADIATION SHIELDING shield underlying tissue from the Whale sharks spend a significant harmful effects of radiation proportion of time in shallow (Myrberg, 1991). Yet one must

125 question why the whale shark Species recognition possesses white regions directly Coloured fin tips are believed to adjacent to darker melanic facilitate species recognition in regions. The whale shark would many species of pelagic requiem likely expose unshielded areas to and hammerhead sharks (family radiation as well as shielded Carcharhinidae),that appear regions each time it entered otherwise superficially similar to shallow water. This suggests that sympatric species (Myrberg 1991). the presence of two adjacent Considering the whale shark’s regions of pigmentation have large size and distinctive body greater benefit than either singly form, it could be argued that they (Myrberg 1991). would be able to achieve species Another shark that might need recognition without the use of such protection is the blacktip distinctive body markings. The reef shark, Carcharhinus Greenland shark, melanopterus, a resident of shallow microcephalus, and the great reef flats that often swims with its hammerhead shark, Sphyrna first out of the water mokarran, are also very large and (Myrberg 1991). The melanin at the have unique body forms, yet lack tip of this fin would clearly shield obvious fin or body markings. the underlying tissue from However, the bluntnose sixgill radiation damage, yet just below shark, griseus, the this melanic region is an , Megachasma extremely white band. Again, this pelagios, the , area would also be exposed to Cetorhinus maximus, the white radiation, raising doubts that shark, Carcharodon carcharias, and radiation shielding is the primary, the , are also very large or even a major, function of with distinctive, if not unique, pigmentation patterns in shallow- body forms. Yet all have water sharks. distinctive body and/ or fin markings (less distinct in large INTRASPECIFIC tiger sharks). This suggests that the COMMUNICATION situation regarding distinctive markings in sharks is rather more A few shark species appear to have complex than simply resulting the ability to transfer information from a need for intraspecific to achieve certain social recognition. functions, such as readiness to fight or mate (Myrberg 1991), and it seems reasonable that most, if Sex recognition not all, sharks share this ability to Body and fin markings are not sex some extent. Such communi- specific in any species of shark cation requires two participants: a and, therefore, do not aid in the signal sender and a signal receiver sex recognition process (Myrberg (Hopkins 1988). These messages are 1991). Rather, there is evidence to usually visual, the optical signal suggest that female pheromones consisting of motor patterns and/ are involved pre-copulatory or body markings. attraction and sex recognition in

126 some species of elasmobranchs hammerhead shark, Sphyrna lewini (Bass 1978; Johnson and Nelson (Klimley 1985), and others. In 1978; Luer and Gilbert 1985; short, agonistic displays are wide- Demski 1990; Gordon 1993). spread among sharks. It is likely that whale sharks also Postural displays use postural displays to establish Intraspecific competition is dominance hierarchies during exhibited when two or more feeding and mating aggregations. individuals of the same species A recent observation of an simultaneously demand use of a interaction between two whale limited resource (Wilson 1975). sharks in the may Contest competition results when provide some evidence for this one competitor actively prevents hypothesis. In this encounter, the another’s access to resources larger of the two sharks banked through aggression or dis- towards the smaller one, forcing it placement, allowing that indi- into tightening circles (G.L. vidual to obtain a greater share of Kooyman, pers. comm.). Eventu- resources. Access to the resource is ally the smaller whale shark fled usually established through the area. During this display, the agonistic behaviour that rarely larger animal presented its takes the form of fighting competitor with its dorsal surface, the location of the markings in (Klimley et al. 1996). Competitors display exaggerated motor question. Further observations of patterns that demonstrate the social displays in whale sharks are unease of the displaying needed before any conclusions individual to the presence of can be made of this possible another and its capacity to inflict function. harm should the competitor remain. The signaler consequently Schooling coordination gains an advantage if the recipient Schooling would provide a heeds the message and withdraws number of benefits to whale (Burghardt 1970). Documented sharks, particularly during the examples of agonistic displays in first years of their lives. A school sharks include the exaggerated of neonate sharks would have swimming display of the gray reef many times the number of eyes shark, Carcharhinus amblyrhynchos and other senses to detect (Johnson and Nelson 1973), and predators than would a solitary tail slapping and breaching in the individual. Predators would be white shark, Carcharodon presented with a visually con- carcharias (Klimley et al. 1996). fusing cluster of constantly Similar behaviours are also known milling bodies bearing bold in the smooth dogfish, Mustelus markings, making it difficult to canis (Allee and Dickinson 1954), single out an individual at which the shark, Sphyrna to strike. When a predator attacks, tiburo, and the blacknose shark, chances are it will be someone else. Carcharhinus acronotus (Myrberg Furthermore, there are hydro- and Gruber 1974), the scalloped dynamic advantages to be gained

127 by being a member of a school. relying on anaerobic glycolysis as Schooling in fishes is coordinated an energy source (accumulating a using both vision and the lactic acid debt) (Kryvi and Eide acoustico-lateralis system 1977). These factors suggest that (Partridge and Pitcher 1980). The neonate whale sharks would have dark bars on the sides of many difficulty keeping up with their schooling fishes allow individuals mother for any extended period. to fixate on the side of a However, a recent observation of neighbour and coordinate an adult whale shark accom- polarised movement (Shaw 1962; panied by 16 juveniles indicates Denton and Rowe 1998). that this may not be the case The limited information on whale (Pillai 2001). Whale shark pups shark parturition obtained from may cluster together for both the single gravid female captured safety and to reduce swimming off Taiwan in 1995 seemed to effort, using their bold body indicate that whale sharks most markings as visual cues to likely give birth to their young coordinate schooling behaviours over a protracted period (Joung et such as parallel orientation. al. 1996). Larger size classes of embryos were free of their INTERSPECIFIC cases and presumably ready to be COMMUNICATION born, while smaller individuals Communication is not restricted were still in their cases and clearly to members of the same species. not yet ready. However, recent Most ethologists include cases of studies on nurse sharks, signal exchange between members Ginglymostoma cirratum, suggest of different species. Body mark- that more developed embryos are ings are used here to assist the retained until the less developed sender to transmit misinform- embryos mature, resulting in the ation, by concealing the sender litter being born at more or less and at the same time increasing its the same time (C.A. Manire and J.C. conspicuousness. In this scenario, Carrier, pers. comm). As each of the signal is optical, the sender is the nine neonate whale sharks the shark and the receiver is the recorded in the literature were shark’s prey. The effect of this taken pelagically (Wolfson 1983; visual signal depends on the Kukuyev 1996; Colman 1997), it is environmental variables that reasonable to believe that whale influence its appearance and on sharks are born more-or-less at the the characteristics of the photo- same time in the open ocean. receptors of the receiver. Whale shark pups have a relatively low Reynolds number Aggressive mimicry when compared with their mother. They also inherit a basic Aggressive mimicry provides a structure featuring an over- predator with the opportunity to whelming predominance of white get much closer to a victim than myotomal muscle which responds otherwise would be the case to sustained high activity by (Myrberg 1991). To attain this

128 proximity, the predator mimics a approaching whale shark, are the signal that is normally attractive outline of its oval mouth and the to, or at least is not avoided by, large caudal fin. The whale shark’s the intended prey (Edmunds body only seems to resolve from 1987). Myrberg’s (1991) examination the visual background after one of the functional relevance of the recognises these cues and strains huge white tipped fins of the to see the rest of the fish. As the , animal gets closer still (within the Carcharhinus longimanus, clearly ‘blending distance’), the shark’s demonstrates this concept. His unique body markings become ‘spot-lure’ theory describes how evident. the silhouette of a nearby oceanic Whale sharks feed on a variety of whitetip is easily seen; but from a planktonic and nektonic prey, distance the body’s silhouette including small crustaceans and becomes indistinct and only the small schooling fishes (Compagno moving white-tipped fins (‘spots’) 1984; Last and Stevens 1994). One remain visible. An observer would of the primary functions of see a ‘pack’ or a ‘school’ of small, schooling in crustaceans and small white objects moving closely fish is to protect its individual together at a distance. Oceanic members from predation. This whitetips are known to prey upon strategy is effective against some of the fastest oceanic predators taking individuals one predatory fishes and it is unlikely at a time (e.g. predatory fish, they could chase down or sneak seabirds), but would appear to be up on them in open water. Since ineffective, if not detrimental, many small prey fish are lightly against bulk-feeding predators coloured and move in schools, it is (Sharpe and Dill 1997) such as the postulated that predatory fish whale shark. The whale shark’s would likely investigate by suction-feeding mechanism is moving toward such ‘prey’. The quite limited in the amount of scenario is that the whitetips spots seawater it can process per unit of lure faster moving prey to a time and consequently whale distance where the shark’s rapid sharks must target dense con- acceleration could overcome centrations of prey (Compagno veering by the predatory fish. 1984). In coastal waters off Evidence is also provided that Ningaloo Reef, whale sharks young oceanic whitetips hide appear to feed primarily on their lures, as they may attract swarms of the tropical euphausiid predators, by wearing a Pseudeuphausia latifrons (Taylor transitional ‘costume’ of black 1994; Wilson and Newbound tipped fins. 2001). The optical effect described in The importance of whether the oceanic whitetip sharks is not whale shark’s outline or its spots apparent from in-water are visible first is questionable observations of whale sharks. The from the perspective of their first visual cues to register, small schooling prey. Rather, the signaling the location of an visual stimulus for the prey at

129 closer distances (within striking pigments sensitive to longer range) should to be considered, as wavelengths (colour vision), the it is at this distance that the group ‘lures’ will be further enhanced by would collectively flee. Schooling stronger contrast against the and fishes, observing background water (McFarland and an approaching whale shark, may Munz 1975). see a ‘pack’ or a ‘school’ of small It should be questioned at this white objects moving closely point whether it would be together. It is reasonable to con- necessary for the whale shark to sider that they might respond to use aggressive mimicry, as it is this stimulus by either doing much more mobile than its prey. nothing, or by moving towards Due to low Reynolds numbers, the ‘school’ with the intention of zooplankton are virtually glued fusing. In maximizing school size, in place by viscous and electro- individual members would be static forces. Rapid avoidance is accorded greater protection from not much easier for small predation. Laboratory studies baitfishes, which have to swim have shown that both schooling much harder than a whale shark crustaceans and fishes will move to overcome viscous forces. towards and merge or fuse with Additionally, suction-feeding another school when presented would significantly extend the with the opportunity (Hamner et ‘striking range’ of the whale shark al. 1982; Pitcher and Wyche 1982). and could surely overpower the White objects reflect maximally feeble swimming abilities of most all wavelengths of the visible prey. spectrum, and are chiefly illuminated by daylight that has traveled the direct path from the CONCLUSION surface to the object and whose In reviewing the body markings radiance is then reflected into the of the whale shark, we conclude eye of an observer. Of course, the that they function primarily to nearer the object is to the surface, conceal the animal in its pelagic the greater the illumination and habitat. Countershading elimi- the more intense the reflection. nates the appearance of solidity The background water contains while disruptive colouration scattered light that has traveled a disrupts surface continuity, longer path and hence has a carrying the eye of the observer narrower spectral radiance curve. through the optically flattened The broader spectral radiance surface of the whale shark’s body reflected off the whale shark’s to patterns that are consistent spots would also more than likely with the animals open ocean contain those wavelengths that habitat. The bold pigmentation are absorbed by the various visual pattern of whale sharks may also pigments possessed by the retina be adaptive in neonates by of an observer, enhancing the facilitating visual coordination of relative brightness of the spots. If schooling in the open ocean, the observer possesses retinal thereby further reducing each

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