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Into the Deep

Into the Deep

 
     
Oct 2013

Words by Georgina Jones & Kerry Sink, Pics by Peter Timm & Barbara Brou

The Coelacanth seems to be a creature of extremes. In most aspects of its biology, from its metabolism to its reproductive processes to its fossil record, it is unusual. It comes from one of the longest existing, least changed vertebrate lines known, and lives in a harsh environment. These extremes have not always been benign. Though its discovery has been associated with high days and holidays, there have also been disasters. Maybe predictably in such a fascinating fish, it has aroused jealous passions in many of the people involved in researching or protecting it.

The coelacanth story began way back when in the Lower Devonian, some 400 million years ago with a beast known as Miguashaia. The fossil record shows that the coelacanth line flourished as time went by, reaching its greatest diversity in shape and habitat in the Triassic period when there were coelacanth species as small as 10cm and giants of 4m.

The first fossil was described by Louis Agassiz, the great Swiss palaeontologist, in 1836. He derived the name coelacanth from the hollow spines supporting the fish’s powerful tail fin. Even in the fossil record, the coelacanth has had the ability to inspire human beings to extremes. When the controversy over Darwin’s theory of evolution began a couple of decades later, proof of a missing link between the fishes and land animals was sought. Coelacanths, with their powerful-looking muscular fins, seemed likely contenders and they were suggested as possible early ancestors of terrestrial vertebrates. 

The most recent coelacanth fossil known, Macropoma, was presumed extinct in the same event that did in the dinosaurs, and that was the end of the story until 1938, when the captain of the I&J trawler Nerine, Hendrik Goosen, caught a strange blue fish trawling in the 40-70 metre depth range off the mouth of the Chalumna River near East London. He was in the habit of handing over any unusual fish he caught to the curator of the East London Museum, and this fish was no exception.

This was how Marjorie Courtenay-Latimer found herself in possession of a large, somewhat smelly fish carcass, just before Christmas. She thought it the most beautiful fish she had ever seen but recognised it as being something out of the ordinary. She tried to get hold of JLB Smith, a self-taught ichthyologist then working as a chemistry lecturer at Rhodes University. He was away on holiday and it was some time before he got back to her, by which time desperate measures had had to be taken to preserve the fish. Being summer, it was hot, and the fish was too big to fit into any of the available refrigeration, so eventually it was taken to a local taxidermist and stuffed. In this process, the vital internal organs were lost, although the publication of the description of what remained caused an international sensation and put Smith (and South African ichthyology) on the world map. This was a fish almost identical to its closest fossil relative, known from 70 million years ago. Smith described himself as being as surprised as if he had come across a dinosaur walking in the street.

Smith decided the fish was a stray and that its normal home would be further north in the Mozambican Channel. Finding an intact specimen was of critical importance in terms of the evolutionary insights it might offer and Smith arranged for a huge reward to be paid to anyone finding the fish. Time went by and it was to be 14 years to the month before a second coelacanth was brought to light. This one had been caught by a line fisherman off the Comoros. Once again, though, it was December, and Smith worried that this second, intact and most valuable specimen would also be degraded. So he called the then Prime Minister, DF Malan, for help. As you do. 

Malan, apparently, whatever his flaws, recognised the discovery as being of great importance and sent an Air Force Dakota to Comoros, then a French colony, with Smith on it. How a major international incident was avoided is unknown. After all, this was a foreign military plane arriving on French soil to remove what must have been seen as French property. But Smith came back to South Africa in happy possession of this most unusual and fascinating fish, his reputation as an ichthyologist assured. He published a much-read book about his discovery, and went on to study many other fish species.

Coelacanth studies after this time became the preserve of the French, who found that local fishermen were accustomed to pulling up two or three a year while night fishing for oilfish. Coelacanths were not targeted because the flesh is oily, contains hard-to-digest compounds such as urea and tends to cause diarrhoea. Close on 200 coelacanths have been caught in this area to date and much about their biology has been learned. 

Though they are classified as bony fish, in evolutionary terms, they are more closely related to reptiles and mammals than they are to bony fish.

This strange many-finned fish is a large creature, reaching  nearly 2 metres in total length and weighing around 100 kilos. Unlike all the other bony fish in the world, coelacanths have lobed fins and they have eight fins in total. There’s one sail-shaped dorsal fin, a second lobed (muscular) dorsal fin, paired pectoral fins, paired pelvic fins, an anal fin in line with the second dorsal fin and a characteristic powerful tail fin which is rounded and has a central lobe with spiny fin rays. The body is covered in large heavy spiny scales. Unlike all other vertebrates, coelacanths have a joint between their upper jaws and the rest of their skulls, which may help in opening their mouths to engulf large prey fishes. Their brains are small, taking up less than 2% of the skull in adult fish, and at the front of the skull is what is known as a rostral organ, of currently unknown function, though it is presumed to be some sort of electroreceptor, particularly since it has three openings to the outside. The eyes are large and have many rods which aid vision in their low light environment. 

Their skeletons are mostly made of cartilage like those of sharks and rays, and their vertebrae are not well-developed. Instead of the vertebral column of adult fish, coelacanths have a thick cartilaginous tube filled with oil, which is flexible and supports the spinal cord. This is called a notochord and is also found in lungfish and some primitive sharks. They have a large fat-filled swimbladder for buoyancy regulation. 

Reproductively, coelacanths are mysterious because though they have internal fertilization, there is so far no evidence of a copulatory organ (as it is known in the trade), the males having only an opening called a cloaca, so just how the sperm is transferred remains unknown. What is known is that coelacanth eggs are huge, being about as big as oranges, and weighing over 300g, the biggest eggs known of all the fishes. The pups are born at about 36cm, having been nourished by the large yolk. Research suggests coelacanths may be pregnant for three years.

Coelacanth biology was only, however, known from dead or dying specimens until an innovative German scientist, Professor Hans Fricke and two associates, managed to begin submersible work in the 1980s on the barren volcanic marine slopes of the Comoros in depths of 120-400 metres. Their studies showed the coelacanth to be a slow-moving fish which rests in caves in groups of up to 16 during the day. Possibly they are conserving energy by staying away from the strong currents in the area, or possibly they are taking shelter from predators such as deep-sea sharks. Their metallic blue-grey bodies covered with irregular white spots are well-camouflaged in the dimly-lit caves, which are composed of basalt and dotted with white oyster shells. They are more active at night, when they emerge from caves to drift slowly 1-3 metres above the slopes, presumably in search of prey. They do not use their limbs for walking over the ocean floor as was once thought, but use a slow sculling motion of their second dorsal and anal fins to swim, rather like sunfish do. They are capable of sudden bursts of speed, when they put their powerful tail fin into action, and seem to use their pectoral fins mainly for turning and stability. They may well be a sort of stealth predator, using slow movements to approach unwary prey and then lunging, much as potato bass do. Fricke observed that their home ranges could be as much as 8km in extent and has never observed any aggression between coelacanths. They also seem to avoid contact with one another, so the mystery of their reproductive processes becomes even more profound. It is thought they may live for up to 100 years, though calculating coelacanth age is fraught with difficulties, since they have not been reliably aged from their scales as many other fish are.

What has been observed and is still not properly understood is the habit coelacanths have of hanging head down while on their nightly rounds. They rotate their bodies so that their heads hang just above the ocean bottom while their tail fins curve at near right-angles to their bodies. It is possible that the enigmatic rostral organ in their snouts is electro receptive and they are picking up prey signals by angling it closer to the ocean floor. It is also possible that this is an alarm response to the submersible, which may be a similar size to that of their deep-ocean predators, or they may also be reacting to electrical signals the submersible emits.

Over the years since their discovery, coelacanths had been caught off various destinations off the African mainland and Madagascar, but in 1998, a couple visiting a fish market in Sulawesi in Indonesia noticed another strange fish. In keeping with the coelacanth tradition of high days and holidays, they were on their honeymoon, and since they were both marine biologists, it perhaps makes more sense that they were visiting a fish market right then. This new animal turned out to be a different species from the East African coelacanth, and was duly named Latimeria menadoensis to differentiate it from the African species, L. chalumnae

Meanwhile in South Africa, the search for coelacanths continued.  And its results were not benign. Coelacanths live in deep water and getting there and back again safely is not a trivial matter. Willem Boshoff, the then marine officer at Sodwana Bay, had studied the offshore profile of the area and thought there might be a chance of coelacanths occurring there. He and Peter Timm. a Trimix specialist and the owner of Triton Dive Lodge, planned an expedition to investigate the possibility. They included Rehan Bouwer, the man who had taught the bulk of the country’s Trimix divers in those days, as well as Johnny Van Der Walt, who had dived the deep canyons off the Comoros and was convinced that the deep water habitats in Sodwana Bay were suitable for coelacanths. In 1998, the team went exploring the Wright Canyon and in the process, Rehan disappeared whilst on one of the sample collection dives in the canyon. Not only that, but no coelacanths were found during this expedition.

Post-dive analysis suggested equipment failure to be the cause of this tragic accident although no one can be sure.  

In late  2000, a group of Trimix divers were on a training dive with Triton Dive Lodge at 104 metres in Jesser Canyon off Sodwana Bay when one of the students noticed a huge eye under an overhang. Closer inspection revealed that the eye belonged to a large fish and that it was in a group of what he was certain were three coelacanths. Peter Timm, the instructor, preoccupied with getting his charges safely to the surface, wasn’t so sure. 

None of the divers had cameras with them and since coelacanths had only ever been seen in much deeper water, 104 metres was a stretch as a credible sighting. 

So they planned another dive. This time, with video cameras so they would have proof. But disaster struck, and the cameraman who was filming the coelacanths lost his life. The extremes of human experience that seem to be associated with coelacanths were evident even on this tragic dive, when the fish were only sighted and videoed right at the end of the dive. Again, three coelacanths were seen, though whether these were the same individuals seen on the previous dive was unknowable. 

The discovery of a population of coelacanths in diveable depths off the South African coast caused a huge stir and the Minister for the Environment and Tourism at the time acted at once to protect the fish and restrict access to the population.   

Sodwana Bay is a part of the iSimangaliso Wetland Park, a World Heritage Site, which has more than 15 deep water canyons running out to sea from very close to shore. It is in these canyons that the Sodwana population of coelacanths make their home. There are important differences between this habitat and that of the Comoros, depth being probably the most interesting one. 

Divers returned to investigate the coelacanths in 2001. Again, three animals were sighted and comparison of the markings suggested that two were matches with previously seen fish. The third was a new fish named Harding after Dennis Harding who first captured Sodwana’s coelacanths on camera. By 2002, Hans Fricke had partnered with the South African Institute of Aquatic Biodiversity (SAIAB), the research facility previously known as the JLB Smith Institute of Ichthyology. They arranged the necessary permits and brought the submersible Jago to Sodwana to investigate. The expedition found 11 coelacanths, two of which were thought likely to be pregnant. . Futher Jago-based expeditions took place and a total of 24 coelacanth individuals were included in a coelacanth catalogue in 2004, each recognised by their distinct white spot patterns on their dark skin. The coelacanths were found in three submarine canyons, Jesser, Wright and Chaka canyons and inshore of Diepgat canyon in depths of 54 to 133 metres. A tissue sample was taken and genetic analysis done in Germany showed that the Sodwana population was very similar to that of the Comoros, so it was concluded that this is a satellite colony, rather than a distinct species. 

A survey conducted in 2005 by remotely operated vehicle (ROV) produced yet more data. Though only one new coelacanth was sighted, investigators found they could get closer to the animals which seemed less disturbed by the ROV than they had been by the submersible. A triumph of the ROV expedition was a sighting of eight coelacanths in one day, a record for Sodwana. 

By the beginning of 2013, 27 coelacanths were known from the deep canyons off Sodwana, with all the recent sightings made by Trimix divers. The initial accidents have thankfully not been added to, despite there now having been eighteen subsequent recreational expeditions, all led by Peter Timm from Triton Dive Lodge. Triton has been involved since the discovery of this elusive fish and all  data collected by them over the years has been made available to various research organisations. They are the only current holder of a permit to dive in these canyons.

In this, the 75th anniversary year of the (re)discovery of the coelacanth, a joint expedition between South African researchers, Trimix divers and scientists from the Natural History Museum in Paris was set up, under the auspices of the iSimangaliso Wetland Park Authority, to further investigate the coelacanth population, behaviour and physiology. Data produced will help guide the Authority’s conservation and protection strategies for this iconic fish. The research is multi-disciplinary and involves bathymetric mapping, population and genetic research, behavioural studies and a broader exploration of biodiversity in the deep water habitats of iSimangaliso.  

During the expedition, three new coelacanths were sighted, including the smallest coelacanth seen at Sodwana, a relative midget at only one metre, as well as Jessie, the first coelacanth seen in 2000. Investigating divers tried unsuccessfully to feed an animal in an attempt to discover how the intercranial joint might work. It is possible that this attempt was doomed from the start since coelacanths are thought to be nocturnal feeders. Mucus swabs were taken for later kinship analysis to establish how the known individuals are related to one another. Multiple synchronized high-tech cameras were used to film coelacanths in motion to further investigate the unique locomotion of coelacanths.

Many mysteries about coelacanths endure: how they reproduce, how long they live, and where the young are, to mention just a few. Since finding them alive though, one thing has become clear. These animals were not the ‘missing link’ between fish and land animals. It is now thought that that position was more likely to have been occupied by an ancestor of the lungfish. For now, these mysterious fish remain in their cavern habitats, unique offshoots of the vertebrate line, the keepers of secrets humans can only guess at.

ACKNOWLEDGEMENTS:

The Department of Science and Technology, the National Research Foundation, the African Coelacanth Ecosystem Program, the South African Institute for Aquatic Biodiversity, the South African National Biodiversity Institute, Andromede Oceanology, Triton Dive Lodge, The Alternative Dive Group, Ezemvelo KZN Wildlife and the iSimangaliso Wetland Park Authority are acknowledged for facilitating research that contributed to this article.

 

Source: The Dive Site

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