I spent the spring of 1969 fishing with a Royal Society expedition in the western Indian Ocean. We aimed to survey as many as possible of the islands and banks north of Madagascar and south of Zanzibar for that most famous of living fossil fishes—Latimeria chalumnae. The coelacanth had been found first off South Africa in 1938 and then off the Comoro Island group northwest of Madagascar in 1952. Given that distribution, there seemed a good chance it would exist elsewhere in the western Indian Ocean. After three months working in the most beautiful coral islands I will ever see, the expedition was a modest success. All sorts of rare and wondrous fishes were found, but in the essentials, we failed—no coelacanths.
All this helped to contribute to the view that Latimeria really is a classic living fossil, endemic to the tiny Comores Archipelago, and that the specimen from South Africa was just a stray. This was a story we could be comfortable with—a relic from the Mesozoic clinging to existence in one tiny godforsaken spot, soon to become totally extinct. But now, 30 years later, everything has become magnificently confused once again. And the story is something of a morality play about the changing course of scientific ideas. Like any good play, the story comes in three acts.
Act One: Enter Latimeria, Stage Right
Act One opened in the South African port of East London on December 22, 1938. As almost everyone knows, there were two principal players. Marjorie Courtenay Latimer (curator of the East London Museum) picked out the fish from a pile that had been saved for her by the men of the trawler Nerine and taken from the bay of the Chalumna River, just to the south. James Leonard Brierly Smith was an eccentric chemist-cum-ichthyologist from what was then Rhodes University College in Grahamstown. Smith identified this strange blue fish despite the inherent absurdity of it all—a living member of a group that had previously been known only from fossils, of which the most recent was some 70 million years old. Even more improbably, he hadn't even seen the fish itself, just a sketch that Miss Latimer sent him. But he was right, and thereafter the story of the coelacanth has always been larger than life—chance events, interesting characters, challenges to orthodoxy.
Act One continued with Smith's search for more specimens, mostly through a poster made up in three languages that he distributed along the whole coast. Persistence was one of Smith's virtues, and eventually it paid off, thanks to another flamboyant character.
Eric Hunt ran the trading schooner N'duwaro between the mainland and the islands of the western Indian Ocean, including the Comores. Hunt had taken a batch of Smith's posters to the Comores after meeting Mrs. Smith in a Zanzibar market late in 1952. It was Hunt to whom, just a few weeks later, word came of the capture of a big strange fish from Anjouan Island. He telegraphed Smith, who had to enlist the help of the South African prime minister for an Air Force plane in which to swoop down on the Comores to collect the specimen, now in rather sad shape. Luckily, after all this effort, it really was a coelacanth, although Smith foolishly tried to convince the world that it was a new genus and species. Glory for Smith? The beginning of a whole new era for him? Not at all.
Although Hunt and Smith had been cheerfully supported by M. Pierre Coudert, Comoran Chef du Territoire, there was "no joy in Mudville" (Paris, that is). The Comores were French territory, and quite understandably national pride and scientific honor were at stake. It soon turned out that the fish was well enough known to some Comoro islanders for there to be a local name for it—ngombessa. Smith had been right. However Act One ends not with Smith as the leading man, but instead with Professors Jacques Millot, an arachnologist, and Jean Anthony, an anthropologist, from Paris.
Act Two: The Plot Thickens
By 1966, some 50 specimens had been caught by Comoran fishermen, using traditional hand lines with a single baited hook at between roughly 100 and 500 meters. In fact, no Westerner had ever caught one (or has yet). It seemed that Latimeria were mostly caught in the first three months of the year, always at night and only from two islands. The idea became popular that they really lived at depths beyond the fishermen's reach and migrated to lesser depths at night, following food species. Then doubt started to grow: The fishing statistics are not an index of the fish's behavior, but rather of the fishermen's! Fishing the deep slopes of these volcanic islands, where there is no protective reef, is dangerous work in a dugout canoe, but the seas are relatively calmer in those months. Despite monetary incentives, the locals are not usually fishing for Latimeria, which is inedible. They are fishing for the more common and reliable Ruvettus pretiosus, prized for the medicinal value of its oil. So everything we know about the distribution of Latimeria may actually be the area of accidental overlap between its range, the range of Ruvettus and the behavior of the fishermen.
In 1966, through another set of strange events, I managed to get to my laboratory at Yale University a freshly frozen specimen. The Comoro Government had decided to raise some foreign currency by selling specimens, and they wrote to museums worldwide to see whether there was any interest. My view was that we already had enough formalin-preserved material; surely a specimen could be frozen instead. Shortly a telephone call from the U.S. Department of State announced that a mysterious shipment addressed to me had become stranded in Marseilles. Only later came the letter from the Comores saying that a specimen had been caught, frozen and put on a passing fruit boat: "Please send $300." Luckily the smart work of the U.S. Commercial Consul in Marseilles saved the day and the fish. A loyal Yale alumnus, he took it from the boat in an embassy car to a frozen-food warehouse and phoned for instructions.
The fresh coelacanth tissues from that specimen gave us a great deal of information about the biology of Latimeria and, from that point on, Act Two became defined by the study of the living fish rather than by its anatomy. Quite naturally, dreams turned to capturing a live specimen. The 1969 expedition failed. In 1972, a new British-U.S.-French venture went to the Comores. At the very end of the trip, a fisherman named Madi Yousouf Kaar brought a coelacanth to shore, alive. It was turned out into a special tank, filmed and observed for several hours.
Pressure for more expeditions grew, and, indeed, further success seemed assured, except that soon afterwards the Comores descended into a political chaos from which they have yet to emerge. Field research in the Comores essentially stopped—except for the efforts of one determined individual.
Dr. Hans Fricke of the Max Planck Institute at Seewiesen, Germany, set out to do what had been dreamed of many times before—to film coelacanths underwater. The obstacle had always been that research submersibles, such as Woods Hole Oceanographic's Alvin, are expensive to operate. So Fricke built his own submersible and, with a private yacht as his mother ship, went to the Comores. Where to look was obvious even if it was based on a flawed analysis. And he succeeded brilliantly, first time. He found live coelacanths between 100 and 200 meters down, living in caves in the deep submarine sides of the volcanic islands.
Coelacanths turn out, as predicted by muscle biochemistry, to be dull creatures, not given to leaping about at high speed, but slowly moving using their paired and median fins in the sculling actions first crudely seen in the 1972 films. But Fricke did not succeed in capturing any major behaviors: no feeding, no copulation, no courting, no fighting off predators. In fact, Fricke concluded that coelacanths lived in every sense a rather empty existence and that the associated fauna were very sparse: no sharks, not much food. Fricke did not observe any juveniles in the cave environment. He did find a vertical nocturnal migration, presumably for feeding—but downwards instead of upwards. Fricke's work seemed to show that coelacanths live in very specialized, sheltered habitats where the lava is most recent and where, therefore, there is no fringing reef—all contributing to create an ecologically depauperate setting. No wonder we hadn't caught any off the richer coral islands to the northwest. And this seemed to confirm that the first South African specimen had been a stray, carried down the Mozambique Channel. In 1988, I forecast that if new sources of coelacanths were to be discovered in the future, they would be on other very young volcanic islands nearby—for example, Europa and Bassas da India.
Act Three: The Butler Didn't Do It
Act Three began with the capture in 1992 of a large coelacanth at a depth of about 50 meters off the coast of Quelimane, Mozambique, some 500 kilometers west of the Comores. A female, she carried no fewer than 26 near-term young. Then in 1995 a specimen was caught in a trawl at 150 meters depth off the southwest coast of Madagascar. Genetic studies showed that the Comoran and Mozambique specimens were strays from the same population. All three non-Comoran fishes had been unknown to local fisherman. All were caught over sandy bottoms, again suggesting atypical behavior (not conforming to the hypothesis, that is). So far, so good. However, nothing is more seductive—or dangerous—than a nice tidy hypothesis.
In July 1997 Arnaz Mehta Erdmann from Berkeley spotted a strange fish in a market at Bershati Market, Manado, at the north tip of Sulawesi (Celebes), Indonesia, 6,000 kilometers east of the Comores. She and her zoologist husband Mark remarked that it looked like a coelacanth, but, as he later told a Washington Post journalist, they assumed that the fish was already known from the Western Pacific. Once the mistake was realized, the search for another specimen was on. In July 1998 another one turned up, caught off the tiny island of Manado Tua.
Abruptly, our carefully crafted schemes are thrown into doubt. We have to reconsider some old questions. What is the full geographic range of the species; how does it live; and—the $64,000 question—how did the coelacanth survive? One of the presumed characteristics of "living fossils" is that their lineages change unusually slowly over time. Thus Latimeria looks superficially very much like a Paleozoic coelacanth, while the living descendants of one of the coelacanth's Devonian sister groups—Osteolepiformes—have diverged enormously (to include, inter alia, ourselves). However, Paleozoic coelacanths were mostly small fishes of shallow brackish and even freshwater ecosystems. Modern Latimeria, by contrast, is very large (up to 2 meters) and totally marine.
There are three main hypotheses to account for the persistence of a living fossil lineage and its morphological conservatism. The defining characteristics allow it to excel at something very specialized; the group shows a very broad general adaptiveness so that it has managed to withstand the slings and arrows of evolutionary fortune; or pure chance.
For coelacanths, the first hypothesis has prevailed—Latimeria chalumnae the species, and by implication its forebears, is a poor thing preferentially living in an unusually bleak ecological setting where competition is low. This hypothesis can accommodate the Indonesian record if, as reported, the island where it was found is also volcanic and geologically extremely young like Anjouan and Grande Comore (less than 1 million years). On the other hand, there seems little depauperate about the non-Comoran settings if they are worth the attentions of commercial fishermen. Instead, however, of adding patch upon patch to old hypotheses, let us imagine that all the known localities with coelacanths had been discovered in this year.
We would obviously conclude first that the fish is broadly, if thinly, distributed over at least the Indian and Western Pacific oceans, and perhaps beyond. Second, we would conclude that the fish lives, at least seasonally, in a wide variety of habitats and at a range of depths from less than 100 to more than 500 meters. Third, since they have all been found near land, a relation to a solid substrate is probably important in the life of Latimeria. Fourth, as two of the five regions where coelacanths have been found involve very young volcanic lava, this environment may be in some way specific to the fish. Fifth, we would start to hypothesize that they hover in bare submarine caves for particular reasons but venture into open water for others. This shift may be daily, as the fish has to feed, and may also have to do with reproduction or some other longer term life-cycle activity. Sixth, we know that the fish catches its prey in short bursts of speed, perhaps aided by its unusual jaw mechanism, but otherwise is a poor swimmer. However, we have no solid evidence to suggest that it uses ocean currents to assist in long-range migration/dispersion. Known specimens may, after all, have lived near where they were caught. Equally, we have no evidence that they do not. Seventh, numbers of individuals at any one location are probably low, at least on very small islands. But total population size, assuming a single species, could be reasonably large. Eight, we would continue to assume that its apparent rarity is partly an artifact of patchy distribution, possibly low population density at any one site and a mismatch between its preferred habitat(s) and the existence of indigenous fisheries at the right depths.
Against all this, how would we rate our previous hypotheses? On the whole, not well. We have led ourselves into flights of invention, trying to tell comprehensive "stories" in order to explain very limited data. In 1989 I ended a previous article about a (then) new development concerning the coelacanth with a reference to Thomas Henry Huxley's notion of scientific tragedy: the slaying of a beautiful hypothesis by an ugly fact. Little did we know….
© Keith Thomson