The biology of Latimeria chalumnae
Feeding habits - Evidence from the prey found in the stomachs of coelacanths indicates that they are predominantly fish-eaters taking lanternfish (Diaphus), cardinal fish (Coranthus), eels (Ilyophis), beardfish (Polymixia), red bream, skates, sharks and also squid and octopus. The vertical head-down position has been found in other drift-feeding fishes. When the coelacanth is close enough to the prey, the mouth is quickly opened, the prey grasped very quickly by the powerful jaws and then swallowed whole.
Sex and growth rate - There is no obvious external difference between male and female coelacanths. Females are more robust than males and grow to a greater size. Large reef-dwelling fishes such as snappers and groupers may live to thirty years, so it is likely that the coelacanth could live longer than that, possibly as long as forty years, or maybe even double that.
Habitat and population size - Latimeria normally occurs at depths of 150 to 700 metres, with most sightings and catches between 150 and 253m. During the day coelacanths retreat to caves where they can rest sheltered from currents and predators (sharks). There is evidence from radio-transmitter tags implanted by Hans Fricke at the Comoros that coelacanths may return repeatedly to the same caves and that they have a home range. When in caves they hover in midwater, rarely touching one another. They appear to be social animals, and aggressive behaviour has not been observed. Where caves or rocky overhangs are rare, coelacanths are hardly ever found. Along the western shores of Grand Comoro the scientists found several occupied caves at depths from 180 to 253 metres. Since Dr Fricke's dives off the Comoros it has become possible to estimate the size of the coelacanth population. The population of adults on the west coast of Grand Comoro was estimated to be about 200. Dr Fricke has never observed juveniles, which probably live in deeper water.
It is not known whether birth rate is dependent on population size or what the predation rate on coelacanths is likely to be. Dr Fricke did observe some large sharks in the habitat of the coelacanths and it is likely that these may prey occasionally on coelacanths.
Reproduction - The reproduction of Latimeria is of a type called ovoviviparity, which means that it has internal fertilization, and the fetuses (called "pups" by biologists) develop in the mother and are born as fully formed juveniles. Only one ovary matures (usually the right) and 19 to 36 enormous eggs about 9 cm in diameter and 320 grams in weight develop inside it. The huge yolk of each egg supplies the nutrients necessary for the pups to grow. The 26 pups found inside the female Mozambique coelacanth indicate that the fish may breed faster and produce more young than was previously thought. This female had been carrying around an extra 12 kilograms of weight.
Coelacanths catches
In 1991 a list was compiled by researchers at the JLB Smith Institute of Ichthyology (now called SAIAB) which included all known specimens of the Indian Ocean coelacanth based on a survey of scientific writings and museum, aquarium and university holdings. At least 172 coelacanths were known then to have been caught since 1938. It was also found that many specimens were leaving the Comoros without being properly documented and about 200 are now known to have been collected.
It was JLB Smith who warned many years ago that the unrestricted catching of coelacanths may threaten their survival, and he proposed that an international society should be formed to protect them. After his death in 1968 the JLB Smith research institute was established in Grahamstown. In 1987 the Coelacanth Conservation Council was founded by an international group of scientists, with the headquarters in Moroni, capital of the Comoro Islands. The coelacanth is now on Appendix I of the Convention on International Trade in Endangered Species (CITES) which prohibits trade in this particular species, and any caught must be released if they are still alive. Now that larger fibreglass outrigger canoes have been introduced into the Comoros by the European Union, and fish aggregating devices are used far from shore, it is hoped that fishermen will concentrate on offshore open water fishing, thus reducing the pressure on nearshore fish populations and potential prey species for the coelacanth. Coelacanths cannot be targeted nor caught on demand no matter what lucrative rewards are offered. Threats to its future survival might arise, however, from commercial interests such as public aquariums and a special coelacanth fishery for museums. In Indonesia during 1998, Japanese groups offered huge sums of money five times to the Manado fishermen for a coelacanth, presumably for display purposes. These offers were refused. Fortunately, by the end of 1998, Dr Erdmann had persuaded the Indonesian government that their coelacanth should be protected as part of their national heritage and that a coelacanth information centre should be set up.
|