 |
Coelacanths, A fossil fish that predates dinosaurs and was thought to have gone extinct has been found alive in the West Indian Ocean off the coast of Madagascar. It was accidentally rediscovered by a group of South African shark hunters. Demand for shark fins and oil has led fishers in southwestern Madagascar to set gill-nets in deeper waters. They are finding and possibly harming previously-unknown populations of these West Indian Ocean Coelacanths.
The first living coelacanth was discovered in 1938 and bears the scientific name Latimeria chalumnae. Professor J.L.B. Smith described the species in 1939, and it was named after its discoverer, Miss Marjorie Courtenay-Latimer. Despite the fact that Latimeria is a separate genus from the fossil forms, all coelacanths share a number of characteristics, including a distinctive shape and lobed fins.
The evolutionary relationships of the coelacanth are a point of debate. Because of the many unusual characters found in coelacanths, there are several competing hypotheses and many unanswered questions. Experts agree that coelacanths are primitive osteichthyans, or bony fishes (as opposed to cartilaginous fishes like sharks and rays), and that their closest living relatives are primitive lungfishes (found in freshwaters in South Africa, Australia, and South America), but they disagree on the coelacanth’s exact evolutionary position. Coelacanths are best described as a branch in the vertebrate lineage’s basal portion, closely related to but distinct from the ancestor of tetrapods (four-legged vertebrates).
Coelacanths are mostly found in the Comoros Islands, which are located between Madagascar and the east coast of Africa in the Western Indian Ocean, but they can also be found along the east African coast and in Indonesian waters. Only one capture (the original one in 1938) has been made in the Indian Ocean, and this specimen has long been thought to be a stray from the Comoran population. Local South African coelacanths, on the other hand, have been spotted in deep canyons, first by divers using mixed gas “rebreathers” and then by scientists using a submersible. Specimens have also been captured off the west coast of Madagascar, as well as off the coasts of Mozambique and Kenya, the latter representing the northernmost locality record along the African coast.
Coelacanths live off the steep rocky slopes of volcanic islands in temperate waters in the “twilight zone,” generally between 500 and 800 feet (152-243 m). The Comoran specimens are known to congregate in “caves” in submarine lava deposits during the day, from which they venture out at night to feed. The two specimens discovered by a submersible in Indonesia were in a 500-foot-deep carbonate cave. Sightings were made off the coast of South Africa at shallower depths, between 300 and 350 feet (91 and 106 metres), beneath ledges and in shallow caves.
In 1938, the discovery of the world’s first living coelacanth off the coast of South Africa made international headlines. Marine biologists were enthralled. A truly amazing “four-legged, living fossil fish” appeared to have risen from the dead. More of these rare and unusual fish were caught off the coasts of South Africa, Tanzania, and the Comoros Islands in the decades after that, and a different coelacanth species was discovered in Indonesian waters.
Coelacanths, the remarkable “fossil fish” that resurfaced from apparent extinction in 1938, may be found in the Indian Ocean’s underwater canyons off Madagascar. Coelacanths have been found in gill-nets set in deep waters to catch sharks for new commercial markets with surprising frequency. The high proportion of pregnant females in recent coelacanth catches in Madagascar is concerning, as they are thought to produce only 140 live babies during their entire lifecycle. Marine scientists are calling for stronger conservation measures to protect this population from the pressures of shark fin trade-related incidental gill-net captures.
Demand for shark fins and oil has led fishers in southwestern Madagascar to set gill-nets in deeper waters. They are finding — and possibly harming — previously-unknown populations of these West Indian Ocean coelacanths.
Non-profit environmental conservation platform Mongabay News
“The advent of deep-set gillnets, or jarifa, for catching sharks, driven by the demand for shark fins and oil from China in the mid- to late 1980s, resulted in an explosion of coelacanth captures in Madagascar and other countries in the Western Indian Ocean,” according to researchers writing in the South African Journal of Science. Deep-set gillnets (jarifa) used by shark fishermen can reach the area where coelacanths congregate, which is about 328 to 492 feet (100 m to 150 m) below the water’s surface.
However coelacanth might face new threats to survive with the increase in shark hunting in international waters.
“The jarifa gillnets used to catch sharks are a relatively new and more deadly innovation as they are large and can be set in deep water,” the researchers wrote in the paper.
The Western Indian Ocean species, Latimeria chalumnae, is classified as Critically Endangered by the IUCN, while a similar species found in the seas around Indonesia (L. menadoensis) is classified as Vulnerable by the IUCN.
