Swimming with Jurassic Sharks
Until very recently, it was widely believed that the Bluntnose Sixgill Shark (Hexanchus griseus) was almost exclusively an inhabitant of the deep-sea. Generally found at depths of 300 to 6,150 feet (90 to 1,875 metres), the Bluntnose Sixgill was known to undertake nightly vertical migrations in many parts of its range and to sporadically visit relatively shallow water areas adjacent to Monterey Canyon, California, and off the southern extreme of South Africa during daylight hours. But the unpredictability of this species' arrival in shallow waters precludes plans to dive with or study them. However, off the coast of British Columbia (BC), Canada, this species seasonally enters shallow coastal waters. Each fall and winter, from August to November, Bluntnose Sixgills can be encountered at depths of 70 to 90 feet (21 to 27 metres) during the day and as shallow as 10 feet (3 metres) during the night at certain locations (notably, Flora Islet off Hornby Island, and Tyler Rock, in Barkley Sound) — to the delight of local divers and underwater photographers. The reliable appearance of Bluntnose Sixgills in depths accessible by scuba provides unprecedented opportunity to observe and study these poorly-known animals.
Between 1992 and 1994, the Canadian Department of Fisheries and Oceans undertook a tagging program in an attempt to quantify the extent of this 'underutilized resource' with a mind toward harvesting these sharks commercially. Fortunately for the sharks, these studies revealed that the population of shallow-water Sixgills was too small to support any but the most limited fishing operations. In the interests of learning more about these poorly-known sharks, I, too, have been studying these shallow-water Sixgills for more than seven years. With the co-operation of many diving friends, we have managed to learn quite a bit about their biology and behavior. From tagging and photographic identification, we learned that some 200 individual sharks seasonally enter shallow waters, many individuals apparently returning to the same sites year after year. Failed attempts to maintain Bluntnose Sixgills in captivity have shown that these sharks are extremely sensitive to light, becoming greatly stressed by even moderate light levels. In addition, shallow coastal waters offer a variety of osmotic stresses very different from the deep-sea environment to which Bluntnose Sixgills are adapted.
What are these normally deep-sea sharks doing in such uncharacteristically shallow water and what do they do while there? I suspect that Bluntnose Sixgills seasonally enter shallow coastal waters off BC in late fall-early winter because obtuse sunlight filtered through plankton blooms allow these light-sensitive sharks to take advantage of the rich feeding to be found in near-shore areas in cold temperate seas. Their arrival coincides well with local salmon and herring runs. Although adults do not seem to feed on either of these fishes, I have found evidence (otoliths, scales, skeletal remains among stomach contents) that the juveniles do feed on Pacific Herring (Clupea pallasii). Likewise, gut contents reveal that while in shallow coastal waters, adult Sixgills feed primarily on Pacific Hagfishes (Eptatretus stoutii), Spiny Dogfish (Squalus acanthias), Lingcod (Ophiodon elongatus) and Cabezon (Scorpaenichthyes marmoratus). During the 1993 field season, I observed a 13-foot (4-metre) male Bluntnose Sixgill capture and eat a Lingcod. The shark came up along a canyon wall, swam up and over the Ling, pushing it down against the bottom with its snout. Thus pinning the Ling to the rocky substrate, the Sixgill with its tail nearly vertical spun around until it could swallow its prey head-first. This maneuver is similar to one reported in a Great Hammerhead (Sphyrna mokarran) feeding upon a Southern Stingray (Dasyatis americana) off Bimini (Strong et al 1990) and likewise seems very economical and efficient, its speed of execution belying the normally languid cruising pace of Sixgill Sharks.
I have discovered evidence that these shallow-water Sixgills are also breeding here. Fresh, white scars appear on the 'nape' (just above the dorsal branchial constrictor and trapezius muscles) of many of the subadult and adult female Sixgills, suggesting that males of the species ritualistically 'nip' females as a prelude to mating. As in many other sharks, mating in Sixgills probably occurs shortly after pupping. Since I have caught newborn Bluntnose Sixgills (identifiable by a distinct vitelline scar on the chest, between the pectoral fins) during July and August in areas (such as Jervis Inlet) just shoreward of the shallow-water haunts of the adults, I suspect that pregnant sharks may drop their young close to shore, where there is plenty of food for the 27-inch (70-centimetre) pups, but relatively few predators large enough to feed on them. Length of gestation period is not known, but is probably longer than 12 months and perhaps even longer than 24 months. (The much smaller Spiny Dogfish — a squaloid, a group moderately closely related to the hexanchoids, the group which includes the Bluntnose Sixgill and other cowsharks — has a gestation period that may be 22 to 24 months long; recent studies by Sho Tanaka and co-workers in Japan suggest that the gestation period of the Frilled Shark [Chlamydoselachus anguineus] — a fellow member of the hexanchoid order — may be 3.5 years or more. If correct, this is by far the longest gestation period of any vertebrate.) Juvenile Sixgills feature an elongated epicaudal (upper lobe of the tail) with a low thrust angle, and employ a relatively inefficient eel-like swimming motion that may make the newborn Sixgills highly vulnerable to predation. This vulnerability may explain the large litter sizes (22 to 108 pups) reported for Bluntnose Sixgills. Likely predators of juveniles of this species in shallow waters include large bony fishes, such as Lingcod and Cabezon, Stellar Sea Lions (Eumetopias jubatus), and Killer Whales (Orcinus orca). No data on juvenile mortality rate in Bluntnose Sixgills are available at this time.
Most Sixgills encountered by divers are between 8 and 15 feet (2.4 and 4.6 metres) in length. The largest Bluntnose Sixgill I have encountered was a female about 15.5 feet (4.7 metres) in length during a dive in Barkley Sound. According to Leonard J.V. Compagno (1984), females of this species mature at a length of between 14.75 and 15.8 feet (4.5 and 4.8 metres), but the Good Doctor gives no data on length at maturity of males. Based on the criteria of viable sperm in the seminiferous tubules and edematous clasper tips, I have learned that male Bluntnose Sixgills — at least off southern BC — mature at a length of about 11 feet (3.4 metres), or about 20% smaller than the females. Determining the age of individual Sixgills — and thereby their age at maturity or longevity — has thus far proven elusive. A well-established method involves staining the vertebreal centra to emphasize the pairs of alternating light and dark bands that correspond to a year's growth, allowing the age of the shark to be determined in a manner analogous to counting tree rings. Perhaps as an adaptation to the generally nutrient-poor deep-sea habitat normally inhabited by these sharks, Bluntnose Sixgills have poorly calcified vertebral centra that render such staining techniques impotent. Mark Saunders of the Pacific Biological Station in Nanaimo, BC, believes he may have discovered a new and reliable method for determining the ages of Sixgills, but has sworn me to secrecy until he can verify the validity of his method and formally publish his data. Given the very cold water inhabited by Sixgills (shallow water temperatures average about 50 degrees Fahrenheit or 10 degrees Celsius year-round; below 660 feet or 200 metes, temperature averages about 39 degrees F or 4 degrees C), I would predict that the animals grow at a positively glacial pace and — barring predation by man or beast — may live a very long time. In the sympatric (occurring in the same place) but much smaller spiny dogfish, females in BC waters do not reach sexual maturity until they are about 35 years old and are known to live at least 70 years. Neptune only knows how long a Bluntnose Sixgill may live.
Perhaps the most interesting aspect of my work on these shallow-water Sixgills has been the opportunity to observe social interactions among them. It is becoming clear that the supposedly 'primitive' Bluntnose Sixgill is behaviorally complex. (The adjective 'primitive' may not be accurate when applied to Bluntnose Sixgills, given this species' numerous specialized adaptations to the deep-sea.) Most shark enthusiasts are probably familiar with the distinctive agonistic (threat) display of the Grey Reef Shark (Carcharhinus amblyrhynchos). One of the major topics of my on-going field research in the Indo-West Pacific is the 'body language' of tropical reef sharks and its role in stabilizing their social hierarchies. To date, I have elicited and studied agonistic behavior in 22 species of sharks — mostly carcharhinoids (the group which includes such familiar sharks as the whalers and hammerheads, among others), but recently I have extended my studies to include orectoloboids (a group which includes wobbegongs, Nurse, Zebra and Whale sharks), a squaloid (the Spiny Dogfish) and one hexanchoid: the shallow-water Sixgill Shark. In approach-withdrawal conflict situations, the Bluntnose Sixgill performs a watered-down — but highly stereotyped — agonistic display. The display in Sixgills consists of pronounced, sustained depression of the pectoral fins, often punctuated by turning broadside to an approaching diver (which may be perceived as a threat). The critical approach distance seems to be less than that for many other shark species (about 1/2 body length of the shark, as opposed to roughly 2 body lengths as I have found for many tropical whaler sharks of the family Carcharhinidae). As with the Grey Reef Shark, the display in shallow-water Sixgills is a graded response, increasing in intensity with degree of escape-route restriction. On one occasion, I observed a 12-foot (3.7-metre) male Sixgill display to an 8-footer (2.5-metre) of undetermined sex and proceed to hoover up the 2-foot (60-centimetre) Lingcod I had secured to the rocky-reef as bait. (Baits are unnecessary to facilitate underwater encounters with these shallow-water Sixgills, as they are concentrated in relatively small areas and are generally curious about divers; I placed bait to provide a focal point for studying competitive interactions among individual Sixgills.)
The occurrence of Bluntnose Sixgills in water accessible by scuba has also enabled me to observe their reactions to divers. In general, the Sixgill Sharks are slow-moving, curious, and non-threatening toward divers. Sometimes Sixgills seem to be 'called' to divers who clink together rocks from the substrate, but at other times the sharks seem to ignore such novel sounds. The Sixgills will allow themselves to be approached quite closely, altering their course only enough to avoid colliding with a diver in their path. But, for all their apparent lethargy, when touched Bluntnose Sixgills may suddenly whip into a tight 'U'-shape and snap most impressively. There are numerous cases of divers being snapped at, but to date no deaths or serious injuries have been recorded. A few underwater photographers have reported that these sharks do not seem to respond to the flash of their strobes, but there are several cases in which strobes have been bitten immediately after firing. In all three cases in which I have been able to interview the photographer after the >ahem< 'incident', he — as all were male (women are apparently too smart to get pushy with such big, toothy animals) — was attempting to take a 'portrait' of the shark from very close range (generally about two feet or 60 centimetres from the shark's head). It sees likely that the shark was responding defensively when its idiosphere ('personal space') was broached, perhaps keying on the localized flux in electromagnetic signature of the strobe as it was re-charging.
Where do the shallow-water Sixgills go in winter and why? I suspect that they retreat into deep water because ambient light levels in relatively shallow waters become uncomfortably high when the autumnal plankton blooms end and the water clears. Like many deep-sea squaloids, Bluntnose Sixgills lack a functional iris, their pupils being permanently dilated to capture what little light filters down to the dark depths they usually inhabit. In 1985, Joel Cohen presented results of a study he made on the visual capabilities of the Bluntnose Sixgill. He found that the retina of this species contains only rods (no cones, thus no color vision), with long outer rod segments averaging 26.4 micrometres in length a spectral sensitivity peaking at about 460 nanometres (a relatively short wavelength corresponding to the deep blue part of the spectrum, with 98% transmission through seawater). Cohen concluded that the Bluntnose Sixgill has a rod-rich retina with very long rod outer segments to give it maximal sensitivity at those wavelengths of light that predominate in the deep-sea. No wonder captive Sixgills typically become highly stressed by even moderate illumination in aquaria! Off the southern coast of BC during the late summer, ambient light levels are quite low below the surface and horizontal visibility may be reduced to less than 15 feet (5 metres), but when the water clears in winter, the underwater environment is noticeably brighter and horizontal visibility may expand to nearly 150 feet (50 metres). Thus, I suspect the profound shift in ambient light levels between fall and winter may compel these light-sensitive sharks to seek the permanent twilight of the deep-sea below 200 metres. I am presently co-operating on the design and construction of long-term sonic telemetry units with which to tag a few of the shallow-water Sixgills, so that my co-workers and I can track their movements through winter and into the subsequent spring and summer. Using telemetric tracking, we will be able to solve the mystery of where at least a few of the shallow-water Sixgills go in winter, which is an important step toward figuring out why they do so.
Although local divers have known about shallow-water Sixgills since about 1960, word has only recently begun to spread about this unique opportunity to observe and photograph these normally deep-sea sharks. Divers from other Canadian provinces, the United States, Japan, South Korea, England and Germany have begun making the trek to British Columbia specifically to dive with and photograph the shallow-water Sixgills. As a result, a significant seasonal dive industry has sprung up around the phenomenon of shallow-water Sixgills in BC. Of course, divers do more than just dive — they hire cars and hotel accommodations, eat at local restaurants, and take in other local attractions (skiing, salmon fishing, etc.) The British Columbia Dive Operators' Association has estimated that visiting divers inject between five and ten million tourist dollars into the local economy each year. In contrast, until recently a cleaned and dressed Sixgill carcass may have fetched as much as $200.00 at a local fish market. Vancouver restaurants formerly sold Sixgill steaks under the name "snow shark", in reference to its remarkably white flesh — but it never caught on as anything more than a novelty Yuppie food. Most Sixgills displayed at fish markets — usually laid out on a 'bed' of crushed ice, with the jaws propped open with a stout stick and its dull eyes staring blankly into next week — aroused more curiosity than sales, eventually to be discarded unceremoniously without any biological data being collected. In a time of enlightened ecological awareness, it seems that rather than butchering and selling off these rare sharks at so many cents a pound, a more rational exploitation of these creatures would be to declare those locations where Bluntnose Sixgills seasonally enter shallow waters to be marine parks, with the sharks as a kind of 'feature attraction'. By doing so, not only would the shallow-water Sixgills benefit, but also the myriad other marine creatures that inhabit these areas year-round.
In response to the federally and provincially tax-funded government test fishery for Sixgills off the west coast of Canada, local dive operators and recreational dive clubs crusaded to have the Sixgills declared a protected species in BC waters. In 1997, the British Columbia government finally decided that the Bluntnose Sixgill is too rare and too poorly known in BC waters to be commercially targeted and made it illegal for recreational or commercial fishermen to possess even a single carcass of this species caught by any means. Bluntnose Sixgills no longer appear at fish markets or on the menu at local restaurants. That I played a small role in co-ordinating and arming local dive groups with the information needed to help convince the provincial government to take steps toward protecting the shallow-water Sixgills in BC brings me deep personal satisfaction. I am continuing to work with local dive groups toward having Flora Islet and Tyler Rock declared marine refugia, with strict 'no-take' laws effective year-round and punishable by severe fine and/or imprisonment. But governmental change on this issue seems to move about as slowly as the Sixgills themselves.
There is only so much one can learn from the dissection of shark carcasses. Dead fish — like dead men — tell few tales. I have examined Sixgills in many parts of the world, mostly as limp, blubbery corpses hauled up from profound depths or as wrinkled, formaldehyde- or alcohol-perfused grotesques jammed and all-but forgotten in coffin-like museum storage vats. To see these animals alive, smoothly functioning under their own power, gives one a new appreciation for their quiet, unassuming beauty. The rare opportunity to observe, photograph, and study them at depth accessible by scuba grants us new insights into the life of a creature whose venerable ancestry extends back to at least the Jurassic Period, some 190 million years ago.
Beyond the research opportunities and cold, hard economics of the matter, I have my own — admittedly romantic — reasons for wanting to protect the shallow-water Sixgills: they're neat to dive with. I vividly remember my first underwater encounter with one, a 14.5-foot (4.4-metre) specimen off Flora Islet in August 1990.
One's first clear view of a large, free-swimming Bluntnose Sixgill in its natural environment is a momentous event. Slowly, the animal resolves spectre-like from the emerald green haze. First to appear is the blunt snout, which overhangs the broad crescent of its mouth. The jaw corners are turned up, seemingly in the whimsical smile of a creature who has seen the dinosaurs come and go — a mere flash in the geologic pan. Then the baleful, almond-shaped eyes glide into view, shining blue-green as though lit from within and rocking lazily forward and back in their sockets. As the shark swims past, its eye rolls tailward to keep me in sight (what does such a creature make of a diver, I wonder? Am I just a 'bad dream' in a somnolent swim that has lasted for decades longer than I have existed?). Now the six gill slits pass, each stark and distinct as knife slashes in paper. Then the short, triangular pectoral fins pass by, each with a little denticle-free 'bald patch' at the axil ('armpit'). As the shark's torso passes, the sheer bulk of its soft grey-brown body becomes apparent — a slowly moving wall of muscle packed behind a tough, armor-like skin studded with tiny denticles that in fresh specimens feel smooth to the touch when stroked head-to-tail. DO NOT TOUCH IT, I remind myself — Sixgills have been known to react aggressively, and their unique cockscomb-shaped lower teeth are those of an animal accustomed to sawing hunks from food items too large to be swallowed whole. Shifting my focus, I try to memorize every detail of this wild animal as it passes a mere armlength away. Next, the pelvic fins glide slowly past, the lack of claspers enabling me to identify her sex. This is followed immediately by the anal fin and — directly above it — a single, blade-like dorsal fin (all hexanchoids have only one dorsal fin, probably the second), as though in stately parade. The lateral line, which began to pass what seems like many minutes ago, is outlined in white and dips curiously at the base of the caudal fin. And finally, this visitor from unimaginable depths of space and time is sculled away by the long, top-heavy tail, the shark never once altering its stately cruising pace.
As the last traces of the shark's subterminal lobe slip back into the emerald gloom with the ease and grace of a magician's silk scarf, I think how lucky I am to see this creature alive and in the context of its natural environment. It is a strangely intimate thing, meeting a Sixgill Shark in her own habitat and on her own terms. The brief glimpses afforded via the clever artifice of deep-sea submersibles and remote video cameras pale by comparison. As my awareness of the chill water returns, I realize that I have actually swum eyeball-to-eyeball with a survivor from the Age of Dinosaurs. This large visitor from an alien, darkling world actually reacted to me — a clumsy, bubbling primate from the blinding world above the liquid skin that separates her realm from mine. As I head toward the surface, back to my own world, I relive one special instant in my mind's eye: for a few seconds, as I looked her in the eye and she in mine, we shared an all-too-brief moment in an unfathomable abyss of space and time. For a few precious breaths of dry bottled air, the hundreds of millions of years separating us evaporated and we were suspended together in an incredible green nothingness. It is an experience both exhilarating and humbling. It is an experience I want other diving naturalists to be able to enjoy.
Here's hoping the shallow-water Sixgills of British Columbia are around for a long, long time to come.
— R. Aidan Martin]
This article elicited a number of follow-up questions and comments. A summary of each inquiry and my responses follow.
"In the book Sharks in Question by Victor G. Springer and Joy P. Gold, it states that there are four species of shark that have six gills. I can only find three: Hexanchus griseus, H.vitulus and the frilled shark, Chlamydoseachus. anguineus. Is there a fourth?"
There is a fourth shark with six pairs of gill slits, the Sixgill Sawshark (Pliotrema warreni) — which grows to a length of about five feet (1.4 metres) and lives in moderately deep water off eastern South Africa. All other sawsharks have five pairs of gill slits and are placed in the genus Pristiophorus (which means, "saw carrier").
There is also a family of six-gilled stingrays, Hexatrygonidae — which includes at least one species (Hexatrygon bickelli) — and possibly as many as six — found in deep waters off South Africa, Taiwan, and Queensland, Australia.
Oh, by the way — and I don't mean to test your patience yet again with seemingly ever-changing scientific names — but Hexanchus vitulus SPRINGER & WALLER 1969 is a junior synonym of Hexanchus nakamurai TENG 1962; the latter is therefore the correct scientific name to use for the bigeye Sixgill Shark.
"It's been reported that captive sevengills occasionally display agonistic behavior ... and audibly snapping their jaws. Have you observed anything like that?"
Captive Notorynchus are well-known for sometimes being aggressive toward divers who brave the same tank (Herald 1968; Reed 1981, 1986). I've never seen this behavior in either Broadnose Sevengills or Bonnetheads, but I have seen exaggerated 'jaw gapes' (though not punctuated by audible snapping) performed by: Grey Nurse Sharks (Carcharias taurus) off Newcastle, NSW, Australia; Shortfin Makos (Isurus oxyrinchus) off San Diego, California; Lemon Sharks (Negaprion brevirostris) off Bimini, Bahama Islands; and Galapagos Sharks (Carcharhinus galapagensis) off Lord Howe Island, Australia. The context of these encounters is entirely consistent with approach-withdrawal conflict situations (sensu Johnson & Nelson 1973, Barlow 1974), and thus may properly be termed 'agonistic' in nature. Jaw gapes are a common component in many fish agonistic displays, and it seems likely that they feature in the normal social interactions of many shark species as well. I'd wager that among the many divers on Shark-L, at least a few can share accounts of similar behaviors in sharks they have encountered.
"Also, given their light sensitivity, any thoughts that their reaction to close-by strobe discharges is a reaction to a painfully bright flash?"
It's certainly feasible. The shallow-water Sixgills do not seem to react strongly to not-so-close flashes (say, 3 to 4 metres away) from photographic strobes, and generally do not react all that strongly to a strobe firing as little as 1 metre from their faces (I have some lovely Sixgill close-up portraits to prove it!). Frankly, the Sixgills don't seem to react too explosively to very much at all, with the exception of being touched.
I suspect that individual Sixgills — like individual people — have varying tolerance levels and that a combination of sustained pursuit, crowding, close-by flashes, and (possibly) accidental contact while maneuvering near the shark's head may conspire to be too much for some Sixgills to take, resulting in a threatening 'snap'. After the fact, all the photographer can recall is that he snapped a picture and the supposedly docile shark suddenly tried to bite him.
In any case, I did not mean to imply that the electromagnetic flux of a re-charging strobe — of itself — instigated those rare cases in which a Sixgill snaps at an underwater photographer, only that the concentrated electromagnetic field may have provided a clear focus for a defensive 'snap'. Most of us, at one time or another, have been temporarily blinded and/or visually disoriented by a camera flash. Perhaps if the thoughtless photographer were close enough and we had ampullae of Lorenzini, we'd be inclined to make like Sean Penn and wallop the offending camera-wielder.
Maybe we have more in common with our sharky friends than we realize.
"Any person other than the original classifier that changes the scientific name and uses his own last name in the new classification should be flogged with a thresher tail. . . Probably another scientist with a big ego"
Actually, this case has more to do with logistical and linguistic difficulties combined with differing interpretations of the formal rules for naming critters than 'big egos' or a desire to 'drive fishermen crazy' on the part of scientists.
As I mentioned in a previous post, the International Commission on Zoological Nomenclature (ICZN) is the international scientific organization that codifies the rules for the taxonomic naming of animals and, when necessary, moderates disputes over priority. In general, the name accompanying earliest formally published description (which must include a detailed description of a purported new species, clarifying how it differs from other known species, and is — in theory, at least — available for study and debate by other scientists) has priority.
Stewart Springer and Richard Waller formally described the Bigeye Sixgill based on 10 specimens from deep waters of the western North Atlantic. They thought this species was a new, smallish and large-eyed Sixgill, closely related to — but readily separable from — the Bluntnose Sixgill (Hexanchus griseus) and therefore named it Hexanchus vitulus (the name means, "six bend" — referring to the gills — and "calf" — referring to its smaller size than griseus, which is also known as the cowshark).
Unfortunately, Springer and Waller did not seem aware that, seven years before, H.-T. Teng had already described the same species from Taiwan as a mimeograph for his doctoral dissertation, but he thought it was a sub-species of the Bluntnose Sixgill, so he named it Hexanchus griseus nakamurai (The last part of the name honors — in Latinized form — his colleague, H. Nakamura. It is fairly common practice to name a new species to honor a person; one could even — in principle — name a new species after one's self — but that's generally regarded as unpardonable egomania and thus bad form. Pity, I would love to see a shark named martini!)
Compagno (1984) was aware of Teng's mimeograph, but disputed whether Teng's paper constitutes formal publication — as defined under Article 8 in the ICZN Code — so he opted to retain the name vitulus in his authoritative and much-used FAO catalogue, Sharks of the World.
In 1991, Toru Taniuchi and Hiroyuki Tachikawa published a short paper (Jap. J. Ichthyol., 38(1): 57-60), in which they compared four specimens from Japanese waters with the descriptions of vitulus and nakamurai and re-assessed the whether Teng's monograph constitutes publication as defined by the ICZN. Taniuchi and Tachikawa found that specimens they examined were sufficiently similar to Teng's (1962) and Springer & Waller's (1969) descriptions that all three samples represent the same species and argued that Teng's (1962) description was, in fact, published within the meaning of the ICZN Code (article 8), because many copies of the paper were distributed to Japanese ichthyologists when it was first issued as Teng's dissertation.
Therefore, Taniuchi and Tachikawa (1991) concluded that the name Hexanchus nakamurai TENG 1962 is a senior synonym of H. vitulus SPRINGER & WALLER 1969, and thus has priority under the ICZN Code. This conclusion has been widely accepted, and Compagno will almost certainly adopt it in the new edition of his FAO catalogue (due out soon!).
One could argue, I suppose, that Springer and Waller should have done their 'homework' more thoroughly and discovered that their specimens were further examples of a species already named half the globe away. But what one has to take into account is the sheer volume of scientific publications and the significant linguistic barriers that separated Japanese and American ichthyologists back in the 1960's. Relatively few English-speaking ichthyologists have taught themselves Japanese. Fortunately for us Anglophones, many Japanese ichthyologists (as well as scientists from many disciplines and many other countries) have taken it upon themselves to become quite fluent in English and frequently publish in that language as well — as English has gradually become the lingua franca of the international scientific community.
Latin or Latinized Greek is still used as the source of taxonomic names as a holdover from the time when Latin was the international language of scholarship, enabling scientists from various countries to share information. One benefit of this widespread use of English as the primary language of communication by the international scientific community is that far fewer important papers go unnoticed simply because the author's first language happens to be something other than English, be it Japanese, Russian, Spanish, Portuguese, French, German, Italian, etc. Should the language of scholarship change once again to something other than English (Chinese, maybe?), the onus will be on us Anglophones to learn that language or fall behind the rest of the scientific community.
The choice — and thereby the power to avoid confusion or frustration — is ours. (So to speak!)
— R. Aidan Martin